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hwpmc_mod.c

/*-
 * Copyright (c) 2003-2006 Joseph Koshy
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 */

#include <sys/cdefs.h>
__FBSDID("$FreeBSD: src/sys/dev/hwpmc/hwpmc_mod.c,v 1.29 2007/06/05 00:00:50 jeff Exp $");

#include <sys/param.h>
#include <sys/eventhandler.h>
#include <sys/jail.h>
#include <sys/kernel.h>
#include <sys/kthread.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/module.h>
#include <sys/mutex.h>
#include <sys/pmc.h>
#include <sys/pmckern.h>
#include <sys/pmclog.h>
#include <sys/priv.h>
#include <sys/proc.h>
#include <sys/queue.h>
#include <sys/resourcevar.h>
#include <sys/sched.h>
#include <sys/signalvar.h>
#include <sys/smp.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/sysent.h>
#include <sys/systm.h>
#include <sys/vnode.h>

#include <sys/linker.h>       /* needs to be after <sys/malloc.h> */

#include <machine/atomic.h>
#include <machine/md_var.h>

/*
 * Types
 */

enum pmc_flags {
      PMC_FLAG_NONE       = 0x00, /* do nothing */
      PMC_FLAG_REMOVE   = 0x01, /* atomically remove entry from hash */
      PMC_FLAG_ALLOCATE = 0x02, /* add entry to hash if not found */
};

/*
 * The offset in sysent where the syscall is allocated.
 */

static int pmc_syscall_num = NO_SYSCALL;
struct pmc_cpu          **pmc_pcpu;  /* per-cpu state */
pmc_value_t       *pmc_pcpu_saved; /* saved PMC values: CSW handling */

#define     PMC_PCPU_SAVED(C,R)     pmc_pcpu_saved[(R) + md->pmd_npmc*(C)]

struct mtx_pool         *pmc_mtxpool;
static int        *pmc_pmcdisp;      /* PMC row dispositions */

#define     PMC_ROW_DISP_IS_FREE(R)       (pmc_pmcdisp[(R)] == 0)
#define     PMC_ROW_DISP_IS_THREAD(R)     (pmc_pmcdisp[(R)] > 0)
#define     PMC_ROW_DISP_IS_STANDALONE(R) (pmc_pmcdisp[(R)] < 0)

#define     PMC_MARK_ROW_FREE(R) do {                               \
      pmc_pmcdisp[(R)] = 0;                                   \
} while (0)

#define     PMC_MARK_ROW_STANDALONE(R) do {                               \
      KASSERT(pmc_pmcdisp[(R)] <= 0, ("[pmc,%d] row disposition error", \
                __LINE__));                                   \
      atomic_add_int(&pmc_pmcdisp[(R)], -1);                        \
      KASSERT(pmc_pmcdisp[(R)] >= (-mp_ncpus), ("[pmc,%d] row "     \
            "disposition error", __LINE__));                  \
} while (0)

#define     PMC_UNMARK_ROW_STANDALONE(R) do {                       \
      atomic_add_int(&pmc_pmcdisp[(R)], 1);                         \
      KASSERT(pmc_pmcdisp[(R)] <= 0, ("[pmc,%d] row disposition error", \
                __LINE__));                                   \
} while (0)

#define     PMC_MARK_ROW_THREAD(R) do {                             \
      KASSERT(pmc_pmcdisp[(R)] >= 0, ("[pmc,%d] row disposition error", \
                __LINE__));                                   \
      atomic_add_int(&pmc_pmcdisp[(R)], 1);                         \
} while (0)

#define     PMC_UNMARK_ROW_THREAD(R) do {                           \
      atomic_add_int(&pmc_pmcdisp[(R)], -1);                        \
      KASSERT(pmc_pmcdisp[(R)] >= 0, ("[pmc,%d] row disposition error", \
                __LINE__));                                   \
} while (0)


/* various event handlers */
static eventhandler_tag pmc_exit_tag, pmc_fork_tag;

/* Module statistics */
struct pmc_op_getdriverstats pmc_stats;

/* Machine/processor dependent operations */
struct pmc_mdep  *md;

/*
 * Hash tables mapping owner processes and target threads to PMCs.
 */

struct mtx pmc_processhash_mtx;           /* spin mutex */
static u_long pmc_processhashmask;
static LIST_HEAD(pmc_processhash, pmc_process)  *pmc_processhash;

/*
 * Hash table of PMC owner descriptors.  This table is protected by
 * the shared PMC "sx" lock.
 */

static u_long pmc_ownerhashmask;
static LIST_HEAD(pmc_ownerhash, pmc_owner)      *pmc_ownerhash;

/*
 * List of PMC owners with system-wide sampling PMCs.
 */

static LIST_HEAD(, pmc_owner)             pmc_ss_owners;


/*
 * Prototypes
 */

#ifdef      DEBUG
static int  pmc_debugflags_sysctl_handler(SYSCTL_HANDLER_ARGS);
static int  pmc_debugflags_parse(char *newstr, char *fence);
#endif

static int  load(struct module *module, int cmd, void *arg);
static int  pmc_attach_process(struct proc *p, struct pmc *pm);
static struct pmc *pmc_allocate_pmc_descriptor(void);
static struct pmc_owner *pmc_allocate_owner_descriptor(struct proc *p);
static int  pmc_attach_one_process(struct proc *p, struct pmc *pm);
static int  pmc_can_allocate_rowindex(struct proc *p, unsigned int ri,
    int cpu);
static int  pmc_can_attach(struct pmc *pm, struct proc *p);
static void pmc_cleanup(void);
static int  pmc_detach_process(struct proc *p, struct pmc *pm);
static int  pmc_detach_one_process(struct proc *p, struct pmc *pm,
    int flags);
static void pmc_destroy_owner_descriptor(struct pmc_owner *po);
static struct pmc_owner *pmc_find_owner_descriptor(struct proc *p);
static int  pmc_find_pmc(pmc_id_t pmcid, struct pmc **pm);
static struct pmc *pmc_find_pmc_descriptor_in_process(struct pmc_owner *po,
    pmc_id_t pmc);
static struct pmc_process *pmc_find_process_descriptor(struct proc *p,
    uint32_t mode);
static void pmc_force_context_switch(void);
static void pmc_link_target_process(struct pmc *pm,
    struct pmc_process *pp);
static void pmc_maybe_remove_owner(struct pmc_owner *po);
static void pmc_process_csw_in(struct thread *td);
static void pmc_process_csw_out(struct thread *td);
static void pmc_process_exit(void *arg, struct proc *p);
static void pmc_process_fork(void *arg, struct proc *p1,
    struct proc *p2, int n);
static void pmc_process_samples(int cpu);
static void pmc_release_pmc_descriptor(struct pmc *pmc);
static void pmc_remove_owner(struct pmc_owner *po);
static void pmc_remove_process_descriptor(struct pmc_process *pp);
static void pmc_restore_cpu_binding(struct pmc_binding *pb);
static void pmc_save_cpu_binding(struct pmc_binding *pb);
static void pmc_select_cpu(int cpu);
static int  pmc_start(struct pmc *pm);
static int  pmc_stop(struct pmc *pm);
static int  pmc_syscall_handler(struct thread *td, void *syscall_args);
static void pmc_unlink_target_process(struct pmc *pmc,
    struct pmc_process *pp);

/*
 * Kernel tunables and sysctl(8) interface.
 */

SYSCTL_NODE(_kern, OID_AUTO, hwpmc, CTLFLAG_RW, 0, "HWPMC parameters");

#ifdef      DEBUG
struct pmc_debugflags pmc_debugflags = PMC_DEBUG_DEFAULT_FLAGS;
char  pmc_debugstr[PMC_DEBUG_STRSIZE];
TUNABLE_STR(PMC_SYSCTL_NAME_PREFIX "debugflags", pmc_debugstr,
    sizeof(pmc_debugstr));
SYSCTL_PROC(_kern_hwpmc, OID_AUTO, debugflags,
    CTLTYPE_STRING|CTLFLAG_RW|CTLFLAG_TUN,
    0, 0, pmc_debugflags_sysctl_handler, "A", "debug flags");
#endif

/*
 * kern.hwpmc.hashrows -- determines the number of rows in the
 * of the hash table used to look up threads
 */

static int pmc_hashsize = PMC_HASH_SIZE;
TUNABLE_INT(PMC_SYSCTL_NAME_PREFIX "hashsize", &pmc_hashsize);
SYSCTL_INT(_kern_hwpmc, OID_AUTO, hashsize, CTLFLAG_TUN|CTLFLAG_RD,
    &pmc_hashsize, 0, "rows in hash tables");

/*
 * kern.hwpmc.nsamples --- number of PC samples per CPU
 */

static int pmc_nsamples = PMC_NSAMPLES;
TUNABLE_INT(PMC_SYSCTL_NAME_PREFIX "nsamples", &pmc_nsamples);
SYSCTL_INT(_kern_hwpmc, OID_AUTO, nsamples, CTLFLAG_TUN|CTLFLAG_RD,
    &pmc_nsamples, 0, "number of PC samples per CPU");

/*
 * kern.hwpmc.mtxpoolsize -- number of mutexes in the mutex pool.
 */

static int pmc_mtxpool_size = PMC_MTXPOOL_SIZE;
TUNABLE_INT(PMC_SYSCTL_NAME_PREFIX "mtxpoolsize", &pmc_mtxpool_size);
SYSCTL_INT(_kern_hwpmc, OID_AUTO, mtxpoolsize, CTLFLAG_TUN|CTLFLAG_RD,
    &pmc_mtxpool_size, 0, "size of spin mutex pool");


/*
 * security.bsd.unprivileged_syspmcs -- allow non-root processes to
 * allocate system-wide PMCs.
 *
 * Allowing unprivileged processes to allocate system PMCs is convenient
 * if system-wide measurements need to be taken concurrently with other
 * per-process measurements.  This feature is turned off by default.
 */

static int pmc_unprivileged_syspmcs = 0;
TUNABLE_INT("security.bsd.unprivileged_syspmcs", &pmc_unprivileged_syspmcs);
SYSCTL_INT(_security_bsd, OID_AUTO, unprivileged_syspmcs, CTLFLAG_RW,
    &pmc_unprivileged_syspmcs, 0,
    "allow unprivileged process to allocate system PMCs");

/*
 * Hash function.  Discard the lower 2 bits of the pointer since
 * these are always zero for our uses.  The hash multiplier is
 * round((2^LONG_BIT) * ((sqrt(5)-1)/2)).
 */

#if   LONG_BIT == 64
#define     _PMC_HM           11400714819323198486u
#elif LONG_BIT == 32
#define     _PMC_HM           2654435769u
#else
#error      Must know the size of 'long' to compile
#endif

#define     PMC_HASH_PTR(P,M) ((((unsigned long) (P) >> 2) * _PMC_HM) & (M))

/*
 * Syscall structures
 */

/* The `sysent' for the new syscall */
static struct sysent pmc_sysent = {
      2,                /* sy_narg */
      pmc_syscall_handler     /* sy_call */
};

static struct syscall_module_data pmc_syscall_mod = {
      load,
      NULL,
      &pmc_syscall_num,
      &pmc_sysent,
      { 0, NULL }
};

static moduledata_t pmc_mod = {
      PMC_MODULE_NAME,
      syscall_module_handler,
      &pmc_syscall_mod
};

DECLARE_MODULE(pmc, pmc_mod, SI_SUB_SMP, SI_ORDER_ANY);
MODULE_VERSION(pmc, PMC_VERSION);

#ifdef      DEBUG
enum pmc_dbgparse_state {
      PMCDS_WS,         /* in whitespace */
      PMCDS_MAJOR,            /* seen a major keyword */
      PMCDS_MINOR
};

static int
pmc_debugflags_parse(char *newstr, char *fence)
{
      char c, *p, *q;
      struct pmc_debugflags *tmpflags;
      int error, found, *newbits, tmp;
      size_t kwlen;

      MALLOC(tmpflags, struct pmc_debugflags *, sizeof(*tmpflags),
          M_PMC, M_WAITOK|M_ZERO);

      p = newstr;
      error = 0;

      for (; p < fence && (c = *p); p++) {

            /* skip white space */
            if (c == ' ' || c == '\t')
                  continue;

            /* look for a keyword followed by "=" */
            for (q = p; p < fence && (c = *p) && c != '='; p++)
                  ;
            if (c != '=') {
                  error = EINVAL;
                  goto done;
            }

            kwlen = p - q;
            newbits = NULL;

            /* lookup flag group name */
#define     DBG_SET_FLAG_MAJ(S,F)                                 \
            if (kwlen == sizeof(S)-1 && strncmp(q, S, kwlen) == 0)      \
                  newbits = &tmpflags->pdb_ ## F;

            DBG_SET_FLAG_MAJ("cpu",       CPU);
            DBG_SET_FLAG_MAJ("csw",       CSW);
            DBG_SET_FLAG_MAJ("logging",   LOG);
            DBG_SET_FLAG_MAJ("module",    MOD);
            DBG_SET_FLAG_MAJ("md",        MDP);
            DBG_SET_FLAG_MAJ("owner",     OWN);
            DBG_SET_FLAG_MAJ("pmc",       PMC);
            DBG_SET_FLAG_MAJ("process",   PRC);
            DBG_SET_FLAG_MAJ("sampling",  SAM);

            if (newbits == NULL) {
                  error = EINVAL;
                  goto done;
            }

            p++;        /* skip the '=' */

            /* Now parse the individual flags */
            tmp = 0;
      newflag:
            for (q = p; p < fence && (c = *p); p++)
                  if (c == ' ' || c == '\t' || c == ',')
                        break;

            /* p == fence or c == ws or c == "," or c == 0 */

            if ((kwlen = p - q) == 0) {
                  *newbits = tmp;
                  continue;
            }

            found = 0;
#define     DBG_SET_FLAG_MIN(S,F)                                 \
            if (kwlen == sizeof(S)-1 && strncmp(q, S, kwlen) == 0)      \
                  tmp |= found = (1 << PMC_DEBUG_MIN_ ## F)

            /* a '*' denotes all possible flags in the group */
            if (kwlen == 1 && *q == '*')
                  tmp = found = ~0;
            /* look for individual flag names */
            DBG_SET_FLAG_MIN("allocaterow", ALR);
            DBG_SET_FLAG_MIN("allocate",  ALL);
            DBG_SET_FLAG_MIN("attach",    ATT);
            DBG_SET_FLAG_MIN("bind",      BND);
            DBG_SET_FLAG_MIN("config",    CFG);
            DBG_SET_FLAG_MIN("exec",      EXC);
            DBG_SET_FLAG_MIN("exit",      EXT);
            DBG_SET_FLAG_MIN("find",      FND);
            DBG_SET_FLAG_MIN("flush",     FLS);
            DBG_SET_FLAG_MIN("fork",      FRK);
            DBG_SET_FLAG_MIN("getbuf",    GTB);
            DBG_SET_FLAG_MIN("hook",      PMH);
            DBG_SET_FLAG_MIN("init",      INI);
            DBG_SET_FLAG_MIN("intr",      INT);
            DBG_SET_FLAG_MIN("linktarget",      TLK);
            DBG_SET_FLAG_MIN("mayberemove", OMR);
            DBG_SET_FLAG_MIN("ops",       OPS);
            DBG_SET_FLAG_MIN("read",      REA);
            DBG_SET_FLAG_MIN("register",  REG);
            DBG_SET_FLAG_MIN("release",   REL);
            DBG_SET_FLAG_MIN("remove",    ORM);
            DBG_SET_FLAG_MIN("sample",    SAM);
            DBG_SET_FLAG_MIN("scheduleio",      SIO);
            DBG_SET_FLAG_MIN("select",    SEL);
            DBG_SET_FLAG_MIN("signal",    SIG);
            DBG_SET_FLAG_MIN("swi",       SWI);
            DBG_SET_FLAG_MIN("swo",       SWO);
            DBG_SET_FLAG_MIN("start",     STA);
            DBG_SET_FLAG_MIN("stop",      STO);
            DBG_SET_FLAG_MIN("syscall",   PMS);
            DBG_SET_FLAG_MIN("unlinktarget", TUL);
            DBG_SET_FLAG_MIN("write",     WRI);
            if (found == 0) {
                  /* unrecognized flag name */
                  error = EINVAL;
                  goto done;
            }

            if (c == 0 || c == ' ' || c == '\t') {    /* end of flag group */
                  *newbits = tmp;
                  continue;
            }

            p++;
            goto newflag;
      }

      /* save the new flag set */
      bcopy(tmpflags, &pmc_debugflags, sizeof(pmc_debugflags));

 done:
      FREE(tmpflags, M_PMC);
      return error;
}

static int
pmc_debugflags_sysctl_handler(SYSCTL_HANDLER_ARGS)
{
      char *fence, *newstr;
      int error;
      unsigned int n;

      (void) arg1; (void) arg2; /* unused parameters */

      n = sizeof(pmc_debugstr);
      MALLOC(newstr, char *, n, M_PMC, M_ZERO|M_WAITOK);
      (void) strlcpy(newstr, pmc_debugstr, n);

      error = sysctl_handle_string(oidp, newstr, n, req);

      /* if there is a new string, parse and copy it */
      if (error == 0 && req->newptr != NULL) {
            fence = newstr + (n < req->newlen ? n : req->newlen + 1);
            if ((error = pmc_debugflags_parse(newstr, fence)) == 0)
                  (void) strlcpy(pmc_debugstr, newstr,
                      sizeof(pmc_debugstr));
      }

      FREE(newstr, M_PMC);

      return error;
}
#endif

/*
 * Concurrency Control
 *
 * The driver manages the following data structures:
 *
 *   - target process descriptors, one per target process
 *   - owner process descriptors (and attached lists), one per owner process
 *   - lookup hash tables for owner and target processes
 *   - PMC descriptors (and attached lists)
 *   - per-cpu hardware state
 *   - the 'hook' variable through which the kernel calls into
 *     this module
 *   - the machine hardware state (managed by the MD layer)
 *
 * These data structures are accessed from:
 *
 * - thread context-switch code
 * - interrupt handlers (possibly on multiple cpus)
 * - kernel threads on multiple cpus running on behalf of user
 *   processes doing system calls
 * - this driver's private kernel threads
 *
 * = Locks and Locking strategy =
 *
 * The driver uses four locking strategies for its operation:
 *
 * - The global SX lock "pmc_sx" is used to protect internal
 *   data structures.
 *
 *   Calls into the module by syscall() start with this lock being
 *   held in exclusive mode.  Depending on the requested operation,
 *   the lock may be downgraded to 'shared' mode to allow more
 *   concurrent readers into the module.  Calls into the module from
 *   other parts of the kernel acquire the lock in shared mode.
 *
 *   This SX lock is held in exclusive mode for any operations that
 *   modify the linkages between the driver's internal data structures.
 *
 *   The 'pmc_hook' function pointer is also protected by this lock.
 *   It is only examined with the sx lock held in exclusive mode.  The
 *   kernel module is allowed to be unloaded only with the sx lock held
 *   in exclusive mode.  In normal syscall handling, after acquiring the
 *   pmc_sx lock we first check that 'pmc_hook' is non-null before
 *   proceeding.  This prevents races between the thread unloading the module
 *   and other threads seeking to use the module.
 *
 * - Lookups of target process structures and owner process structures
 *   cannot use the global "pmc_sx" SX lock because these lookups need
 *   to happen during context switches and in other critical sections
 *   where sleeping is not allowed.  We protect these lookup tables
 *   with their own private spin-mutexes, "pmc_processhash_mtx" and
 *   "pmc_ownerhash_mtx".
 *
 * - Interrupt handlers work in a lock free manner.  At interrupt
 *   time, handlers look at the PMC pointer (phw->phw_pmc) configured
 *   when the PMC was started.  If this pointer is NULL, the interrupt
 *   is ignored after updating driver statistics.  We ensure that this
 *   pointer is set (using an atomic operation if necessary) before the
 *   PMC hardware is started.  Conversely, this pointer is unset atomically
 *   only after the PMC hardware is stopped.
 *
 *   We ensure that everything needed for the operation of an
 *   interrupt handler is available without it needing to acquire any
 *   locks.  We also ensure that a PMC's software state is destroyed only
 *   after the PMC is taken off hardware (on all CPUs).
 *
 * - Context-switch handling with process-private PMCs needs more
 *   care.
 *
 *   A given process may be the target of multiple PMCs.  For example,
 *   PMCATTACH and PMCDETACH may be requested by a process on one CPU
 *   while the target process is running on another.  A PMC could also
 *   be getting released because its owner is exiting.  We tackle
 *   these situations in the following manner:
 *
 *   - each target process structure 'pmc_process' has an array
 *     of 'struct pmc *' pointers, one for each hardware PMC.
 *
 *   - At context switch IN time, each "target" PMC in RUNNING state
 *     gets started on hardware and a pointer to each PMC is copied into
 *     the per-cpu phw array.  The 'runcount' for the PMC is
 *     incremented.
 *
 *   - At context switch OUT time, all process-virtual PMCs are stopped
 *     on hardware.  The saved value is added to the PMCs value field
 *     only if the PMC is in a non-deleted state (the PMCs state could
 *     have changed during the current time slice).
 *
 *     Note that since in-between a switch IN on a processor and a switch
 *     OUT, the PMC could have been released on another CPU.  Therefore
 *     context switch OUT always looks at the hardware state to turn
 *     OFF PMCs and will update a PMC's saved value only if reachable
 *     from the target process record.
 *
 *   - OP PMCRELEASE could be called on a PMC at any time (the PMC could
 *     be attached to many processes at the time of the call and could
 *     be active on multiple CPUs).
 *
 *     We prevent further scheduling of the PMC by marking it as in
 *     state 'DELETED'.  If the runcount of the PMC is non-zero then
 *     this PMC is currently running on a CPU somewhere.  The thread
 *     doing the PMCRELEASE operation waits by repeatedly doing a
 *     pause() till the runcount comes to zero.
 *
 * The contents of a PMC descriptor (struct pmc) are protected using
 * a spin-mutex.  In order to save space, we use a mutex pool.
 *
 * In terms of lock types used by witness(4), we use:
 * - Type "pmc-sx", used by the global SX lock.
 * - Type "pmc-sleep", for sleep mutexes used by logger threads.
 * - Type "pmc-per-proc", for protecting PMC owner descriptors.
 * - Type "pmc-leaf", used for all other spin mutexes.
 */

/*
 * save the cpu binding of the current kthread
 */

static void
pmc_save_cpu_binding(struct pmc_binding *pb)
{
      PMCDBG(CPU,BND,2, "%s", "save-cpu");
      thread_lock(curthread);
      pb->pb_bound = sched_is_bound(curthread);
      pb->pb_cpu   = curthread->td_oncpu;
      thread_unlock(curthread);
      PMCDBG(CPU,BND,2, "save-cpu cpu=%d", pb->pb_cpu);
}

/*
 * restore the cpu binding of the current thread
 */

static void
pmc_restore_cpu_binding(struct pmc_binding *pb)
{
      PMCDBG(CPU,BND,2, "restore-cpu curcpu=%d restore=%d",
          curthread->td_oncpu, pb->pb_cpu);
      thread_lock(curthread);
      if (pb->pb_bound)
            sched_bind(curthread, pb->pb_cpu);
      else
            sched_unbind(curthread);
      thread_unlock(curthread);
      PMCDBG(CPU,BND,2, "%s", "restore-cpu done");
}

/*
 * move execution over the specified cpu and bind it there.
 */

static void
pmc_select_cpu(int cpu)
{
      KASSERT(cpu >= 0 && cpu < mp_ncpus,
          ("[pmc,%d] bad cpu number %d", __LINE__, cpu));

      /* never move to a disabled CPU */
      KASSERT(pmc_cpu_is_disabled(cpu) == 0, ("[pmc,%d] selecting "
          "disabled CPU %d", __LINE__, cpu));

      PMCDBG(CPU,SEL,2, "select-cpu cpu=%d", cpu);
      thread_lock(curthread);
      sched_bind(curthread, cpu);
      thread_unlock(curthread);

      KASSERT(curthread->td_oncpu == cpu,
          ("[pmc,%d] CPU not bound [cpu=%d, curr=%d]", __LINE__,
            cpu, curthread->td_oncpu));

      PMCDBG(CPU,SEL,2, "select-cpu cpu=%d ok", cpu);
}

/*
 * Force a context switch.
 *
 * We do this by pause'ing for 1 tick -- invoking mi_switch() is not
 * guaranteed to force a context switch.
 */

static void
pmc_force_context_switch(void)
{

      pause("pmcctx", 1);
}

/*
 * Get the file name for an executable.  This is a simple wrapper
 * around vn_fullpath(9).
 */

static void
pmc_getfilename(struct vnode *v, char **fullpath, char **freepath)
{
      struct thread *td;

      td = curthread;
      *fullpath = "unknown";
      *freepath = NULL;
      vn_lock(v, LK_CANRECURSE | LK_EXCLUSIVE | LK_RETRY, td);
      vn_fullpath(td, v, fullpath, freepath);
      VOP_UNLOCK(v, 0, td);
}

/*
 * remove an process owning PMCs
 */

void
pmc_remove_owner(struct pmc_owner *po)
{
      struct pmc *pm, *tmp;

      sx_assert(&pmc_sx, SX_XLOCKED);

      PMCDBG(OWN,ORM,1, "remove-owner po=%p", po);

      /* Remove descriptor from the owner hash table */
      LIST_REMOVE(po, po_next);

      /* release all owned PMC descriptors */
      LIST_FOREACH_SAFE(pm, &po->po_pmcs, pm_next, tmp) {
            PMCDBG(OWN,ORM,2, "pmc=%p", pm);
            KASSERT(pm->pm_owner == po,
                ("[pmc,%d] owner %p != po %p", __LINE__, pm->pm_owner, po));

            pmc_release_pmc_descriptor(pm);     /* will unlink from the list */
      }

      KASSERT(po->po_sscount == 0,
          ("[pmc,%d] SS count not zero", __LINE__));
      KASSERT(LIST_EMPTY(&po->po_pmcs),
          ("[pmc,%d] PMC list not empty", __LINE__));

      /* de-configure the log file if present */
      if (po->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_deconfigure_log(po);
}

/*
 * remove an owner process record if all conditions are met.
 */

static void
pmc_maybe_remove_owner(struct pmc_owner *po)
{

      PMCDBG(OWN,OMR,1, "maybe-remove-owner po=%p", po);

      /*
       * Remove owner record if
       * - this process does not own any PMCs
       * - this process has not allocated a system-wide sampling buffer
       */

      if (LIST_EMPTY(&po->po_pmcs) &&
          ((po->po_flags & PMC_PO_OWNS_LOGFILE) == 0)) {
            pmc_remove_owner(po);
            pmc_destroy_owner_descriptor(po);
      }
}

/*
 * Add an association between a target process and a PMC.
 */

static void
pmc_link_target_process(struct pmc *pm, struct pmc_process *pp)
{
      int ri;
      struct pmc_target *pt;

      sx_assert(&pmc_sx, SX_XLOCKED);

      KASSERT(pm != NULL && pp != NULL,
          ("[pmc,%d] Null pm %p or pp %p", __LINE__, pm, pp));
      KASSERT(PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)),
          ("[pmc,%d] Attaching a non-process-virtual pmc=%p to pid=%d",
            __LINE__, pm, pp->pp_proc->p_pid));
      KASSERT(pp->pp_refcnt >= 0 && pp->pp_refcnt < ((int) md->pmd_npmc - 1),
          ("[pmc,%d] Illegal reference count %d for process record %p",
            __LINE__, pp->pp_refcnt, (void *) pp));

      ri = PMC_TO_ROWINDEX(pm);

      PMCDBG(PRC,TLK,1, "link-target pmc=%p ri=%d pmc-process=%p",
          pm, ri, pp);

#ifdef      DEBUG
      LIST_FOREACH(pt, &pm->pm_targets, pt_next)
          if (pt->pt_process == pp)
                KASSERT(0, ("[pmc,%d] pp %p already in pmc %p targets",
                        __LINE__, pp, pm));
#endif

      MALLOC(pt, struct pmc_target *, sizeof(struct pmc_target),
          M_PMC, M_ZERO|M_WAITOK);

      pt->pt_process = pp;

      LIST_INSERT_HEAD(&pm->pm_targets, pt, pt_next);

      atomic_store_rel_ptr((uintptr_t *)&pp->pp_pmcs[ri].pp_pmc,
          (uintptr_t)pm);

      if (pm->pm_owner->po_owner == pp->pp_proc)
            pm->pm_flags |= PMC_F_ATTACHED_TO_OWNER;

      /*
       * Initialize the per-process values at this row index.
       */
      pp->pp_pmcs[ri].pp_pmcval = PMC_TO_MODE(pm) == PMC_MODE_TS ?
          pm->pm_sc.pm_reloadcount : 0;

      pp->pp_refcnt++;

}

/*
 * Removes the association between a target process and a PMC.
 */

static void
pmc_unlink_target_process(struct pmc *pm, struct pmc_process *pp)
{
      int ri;
      struct proc *p;
      struct pmc_target *ptgt;

      sx_assert(&pmc_sx, SX_XLOCKED);

      KASSERT(pm != NULL && pp != NULL,
          ("[pmc,%d] Null pm %p or pp %p", __LINE__, pm, pp));

      KASSERT(pp->pp_refcnt >= 1 && pp->pp_refcnt < (int) md->pmd_npmc,
          ("[pmc,%d] Illegal ref count %d on process record %p",
            __LINE__, pp->pp_refcnt, (void *) pp));

      ri = PMC_TO_ROWINDEX(pm);

      PMCDBG(PRC,TUL,1, "unlink-target pmc=%p ri=%d pmc-process=%p",
          pm, ri, pp);

      KASSERT(pp->pp_pmcs[ri].pp_pmc == pm,
          ("[pmc,%d] PMC ri %d mismatch pmc %p pp->[ri] %p", __LINE__,
            ri, pm, pp->pp_pmcs[ri].pp_pmc));

      pp->pp_pmcs[ri].pp_pmc = NULL;
      pp->pp_pmcs[ri].pp_pmcval = (pmc_value_t) 0;

      /* Remove owner-specific flags */
      if (pm->pm_owner->po_owner == pp->pp_proc) {
            pp->pp_flags &= ~PMC_PP_ENABLE_MSR_ACCESS;
            pm->pm_flags &= ~PMC_F_ATTACHED_TO_OWNER;
      }

      pp->pp_refcnt--;

      /* Remove the target process from the PMC structure */
      LIST_FOREACH(ptgt, &pm->pm_targets, pt_next)
            if (ptgt->pt_process == pp)
                  break;

      KASSERT(ptgt != NULL, ("[pmc,%d] process %p (pp: %p) not found "
                "in pmc %p", __LINE__, pp->pp_proc, pp, pm));

      LIST_REMOVE(ptgt, pt_next);
      FREE(ptgt, M_PMC);

      /* if the PMC now lacks targets, send the owner a SIGIO */
      if (LIST_EMPTY(&pm->pm_targets)) {
            p = pm->pm_owner->po_owner;
            PROC_LOCK(p);
            psignal(p, SIGIO);
            PROC_UNLOCK(p);

            PMCDBG(PRC,SIG,2, "signalling proc=%p signal=%d", p,
                SIGIO);
      }
}

/*
 * Check if PMC 'pm' may be attached to target process 't'.
 */

static int
pmc_can_attach(struct pmc *pm, struct proc *t)
{
      struct proc *o;         /* pmc owner */
      struct ucred *oc, *tc;  /* owner, target credentials */
      int decline_attach, i;

      /*
       * A PMC's owner can always attach that PMC to itself.
       */

      if ((o = pm->pm_owner->po_owner) == t)
            return 0;

      PROC_LOCK(o);
      oc = o->p_ucred;
      crhold(oc);
      PROC_UNLOCK(o);

      PROC_LOCK(t);
      tc = t->p_ucred;
      crhold(tc);
      PROC_UNLOCK(t);

      /*
       * The effective uid of the PMC owner should match at least one
       * of the {effective,real,saved} uids of the target process.
       */

      decline_attach = oc->cr_uid != tc->cr_uid &&
          oc->cr_uid != tc->cr_svuid &&
          oc->cr_uid != tc->cr_ruid;

      /*
       * Every one of the target's group ids, must be in the owner's
       * group list.
       */
      for (i = 0; !decline_attach && i < tc->cr_ngroups; i++)
            decline_attach = !groupmember(tc->cr_groups[i], oc);

      /* check the read and saved gids too */
      if (decline_attach == 0)
            decline_attach = !groupmember(tc->cr_rgid, oc) ||
                !groupmember(tc->cr_svgid, oc);

      crfree(tc);
      crfree(oc);

      return !decline_attach;
}

/*
 * Attach a process to a PMC.
 */

static int
pmc_attach_one_process(struct proc *p, struct pmc *pm)
{
      int ri;
      char *fullpath, *freepath;
      struct pmc_process      *pp;

      sx_assert(&pmc_sx, SX_XLOCKED);

      PMCDBG(PRC,ATT,2, "attach-one pm=%p ri=%d proc=%p (%d, %s)", pm,
          PMC_TO_ROWINDEX(pm), p, p->p_pid, p->p_comm);

      /*
       * Locate the process descriptor corresponding to process 'p',
       * allocating space as needed.
       *
       * Verify that rowindex 'pm_rowindex' is free in the process
       * descriptor.
       *
       * If not, allocate space for a descriptor and link the
       * process descriptor and PMC.
       */
      ri = PMC_TO_ROWINDEX(pm);

      if ((pp = pmc_find_process_descriptor(p, PMC_FLAG_ALLOCATE)) == NULL)
            return ENOMEM;

      if (pp->pp_pmcs[ri].pp_pmc == pm) /* already present at slot [ri] */
            return EEXIST;

      if (pp->pp_pmcs[ri].pp_pmc != NULL)
            return EBUSY;

      pmc_link_target_process(pm, pp);

      if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)) &&
          (pm->pm_flags & PMC_F_ATTACHED_TO_OWNER) == 0)
            pm->pm_flags |= PMC_F_NEEDS_LOGFILE;

      pm->pm_flags |= PMC_F_ATTACH_DONE; /* mark as attached */

      /* issue an attach event to a configured log file */
      if (pm->pm_owner->po_flags & PMC_PO_OWNS_LOGFILE) {
            pmc_getfilename(p->p_textvp, &fullpath, &freepath);
            pmclog_process_pmcattach(pm, p->p_pid, fullpath);
            if (freepath)
                  FREE(freepath, M_TEMP);
      }
      /* mark process as using HWPMCs */
      PROC_LOCK(p);
      p->p_flag |= P_HWPMC;
      PROC_UNLOCK(p);

      return 0;
}

/*
 * Attach a process and optionally its children
 */

static int
pmc_attach_process(struct proc *p, struct pmc *pm)
{
      int error;
      struct proc *top;

      sx_assert(&pmc_sx, SX_XLOCKED);

      PMCDBG(PRC,ATT,1, "attach pm=%p ri=%d proc=%p (%d, %s)", pm,
          PMC_TO_ROWINDEX(pm), p, p->p_pid, p->p_comm);


      /*
       * If this PMC successfully allowed a GETMSR operation
       * in the past, disallow further ATTACHes.
       */

      if ((pm->pm_flags & PMC_PP_ENABLE_MSR_ACCESS) != 0)
            return EPERM;

      if ((pm->pm_flags & PMC_F_DESCENDANTS) == 0)
            return pmc_attach_one_process(p, pm);

      /*
       * Traverse all child processes, attaching them to
       * this PMC.
       */

      sx_slock(&proctree_lock);

      top = p;

      for (;;) {
            if ((error = pmc_attach_one_process(p, pm)) != 0)
                  break;
            if (!LIST_EMPTY(&p->p_children))
                  p = LIST_FIRST(&p->p_children);
            else for (;;) {
                  if (p == top)
                        goto done;
                  if (LIST_NEXT(p, p_sibling)) {
                        p = LIST_NEXT(p, p_sibling);
                        break;
                  }
                  p = p->p_pptr;
            }
      }

      if (error)
            (void) pmc_detach_process(top, pm);

 done:
      sx_sunlock(&proctree_lock);
      return error;
}

/*
 * Detach a process from a PMC.  If there are no other PMCs tracking
 * this process, remove the process structure from its hash table.  If
 * 'flags' contains PMC_FLAG_REMOVE, then free the process structure.
 */

static int
pmc_detach_one_process(struct proc *p, struct pmc *pm, int flags)
{
      int ri;
      struct pmc_process *pp;

      sx_assert(&pmc_sx, SX_XLOCKED);

      KASSERT(pm != NULL,
          ("[pmc,%d] null pm pointer", __LINE__));

      ri = PMC_TO_ROWINDEX(pm);

      PMCDBG(PRC,ATT,2, "detach-one pm=%p ri=%d proc=%p (%d, %s) flags=0x%x",
          pm, ri, p, p->p_pid, p->p_comm, flags);

      if ((pp = pmc_find_process_descriptor(p, 0)) == NULL)
            return ESRCH;

      if (pp->pp_pmcs[ri].pp_pmc != pm)
            return EINVAL;

      pmc_unlink_target_process(pm, pp);

      /* Issue a detach entry if a log file is configured */
      if (pm->pm_owner->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_process_pmcdetach(pm, p->p_pid);

      /*
       * If there are no PMCs targetting this process, we remove its
       * descriptor from the target hash table and unset the P_HWPMC
       * flag in the struct proc.
       */
      KASSERT(pp->pp_refcnt >= 0 && pp->pp_refcnt < (int) md->pmd_npmc,
          ("[pmc,%d] Illegal refcnt %d for process struct %p",
            __LINE__, pp->pp_refcnt, pp));

      if (pp->pp_refcnt != 0) /* still a target of some PMC */
            return 0;

      pmc_remove_process_descriptor(pp);

      if (flags & PMC_FLAG_REMOVE)
            FREE(pp, M_PMC);

      PROC_LOCK(p);
      p->p_flag &= ~P_HWPMC;
      PROC_UNLOCK(p);

      return 0;
}

/*
 * Detach a process and optionally its descendants from a PMC.
 */

static int
pmc_detach_process(struct proc *p, struct pmc *pm)
{
      struct proc *top;

      sx_assert(&pmc_sx, SX_XLOCKED);

      PMCDBG(PRC,ATT,1, "detach pm=%p ri=%d proc=%p (%d, %s)", pm,
          PMC_TO_ROWINDEX(pm), p, p->p_pid, p->p_comm);

      if ((pm->pm_flags & PMC_F_DESCENDANTS) == 0)
            return pmc_detach_one_process(p, pm, PMC_FLAG_REMOVE);

      /*
       * Traverse all children, detaching them from this PMC.  We
       * ignore errors since we could be detaching a PMC from a
       * partially attached proc tree.
       */

      sx_slock(&proctree_lock);

      top = p;

      for (;;) {
            (void) pmc_detach_one_process(p, pm, PMC_FLAG_REMOVE);

            if (!LIST_EMPTY(&p->p_children))
                  p = LIST_FIRST(&p->p_children);
            else for (;;) {
                  if (p == top)
                        goto done;
                  if (LIST_NEXT(p, p_sibling)) {
                        p = LIST_NEXT(p, p_sibling);
                        break;
                  }
                  p = p->p_pptr;
            }
      }

 done:
      sx_sunlock(&proctree_lock);

      if (LIST_EMPTY(&pm->pm_targets))
            pm->pm_flags &= ~PMC_F_ATTACH_DONE;

      return 0;
}


/*
 * Thread context switch IN
 */

static void
pmc_process_csw_in(struct thread *td)
{
      int cpu;
      unsigned int ri;
      struct pmc *pm;
      struct proc *p;
      struct pmc_cpu *pc;
      struct pmc_hw *phw;
      struct pmc_process *pp;
      pmc_value_t newvalue;

      p = td->td_proc;

      if ((pp = pmc_find_process_descriptor(p, PMC_FLAG_NONE)) == NULL)
            return;

      KASSERT(pp->pp_proc == td->td_proc,
          ("[pmc,%d] not my thread state", __LINE__));

      critical_enter(); /* no preemption from this point */

      cpu = PCPU_GET(cpuid); /* td->td_oncpu is invalid */

      PMCDBG(CSW,SWI,1, "cpu=%d proc=%p (%d, %s) pp=%p", cpu, p,
          p->p_pid, p->p_comm, pp);

      KASSERT(cpu >= 0 && cpu < mp_ncpus,
          ("[pmc,%d] wierd CPU id %d", __LINE__, cpu));

      pc = pmc_pcpu[cpu];

      for (ri = 0; ri < md->pmd_npmc; ri++) {

            if ((pm = pp->pp_pmcs[ri].pp_pmc) == NULL)
                  continue;

            KASSERT(PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)),
                ("[pmc,%d] Target PMC in non-virtual mode (%d)",
                  __LINE__, PMC_TO_MODE(pm)));

            KASSERT(PMC_TO_ROWINDEX(pm) == ri,
                ("[pmc,%d] Row index mismatch pmc %d != ri %d",
                  __LINE__, PMC_TO_ROWINDEX(pm), ri));

            /*
             * Only PMCs that are marked as 'RUNNING' need
             * be placed on hardware.
             */

            if (pm->pm_state != PMC_STATE_RUNNING)
                  continue;

            /* increment PMC runcount */
            atomic_add_rel_32(&pm->pm_runcount, 1);

            /* configure the HWPMC we are going to use. */
            md->pmd_config_pmc(cpu, ri, pm);

            phw = pc->pc_hwpmcs[ri];

            KASSERT(phw != NULL,
                ("[pmc,%d] null hw pointer", __LINE__));

            KASSERT(phw->phw_pmc == pm,
                ("[pmc,%d] hw->pmc %p != pmc %p", __LINE__,
                  phw->phw_pmc, pm));

            /*
             * Write out saved value and start the PMC.
             *
             * Sampling PMCs use a per-process value, while
             * counting mode PMCs use a per-pmc value that is
             * inherited across descendants.
             */
            if (PMC_TO_MODE(pm) == PMC_MODE_TS) {
                  mtx_pool_lock_spin(pmc_mtxpool, pm);
                  newvalue = PMC_PCPU_SAVED(cpu,ri) =
                      pp->pp_pmcs[ri].pp_pmcval;
                  mtx_pool_unlock_spin(pmc_mtxpool, pm);
            } else {
                  KASSERT(PMC_TO_MODE(pm) == PMC_MODE_TC,
                      ("[pmc,%d] illegal mode=%d", __LINE__,
                      PMC_TO_MODE(pm)));
                  mtx_pool_lock_spin(pmc_mtxpool, pm);
                  newvalue = PMC_PCPU_SAVED(cpu, ri) =
                      pm->pm_gv.pm_savedvalue;
                  mtx_pool_unlock_spin(pmc_mtxpool, pm);
            }

            PMCDBG(CSW,SWI,1,"cpu=%d ri=%d new=%jd", cpu, ri, newvalue);

            md->pmd_write_pmc(cpu, ri, newvalue);
            md->pmd_start_pmc(cpu, ri);
      }

      /*
       * perform any other architecture/cpu dependent thread
       * switch-in actions.
       */

      (void) (*md->pmd_switch_in)(pc, pp);

      critical_exit();

}

/*
 * Thread context switch OUT.
 */

static void
pmc_process_csw_out(struct thread *td)
{
      int cpu;
      enum pmc_mode mode;
      unsigned int ri;
      struct pmc *pm;
      struct proc *p;
      struct pmc_cpu *pc;
      struct pmc_process *pp;
      int64_t tmp;
      pmc_value_t newvalue;

      /*
       * Locate our process descriptor; this may be NULL if
       * this process is exiting and we have already removed
       * the process from the target process table.
       *
       * Note that due to kernel preemption, multiple
       * context switches may happen while the process is
       * exiting.
       *
       * Note also that if the target process cannot be
       * found we still need to deconfigure any PMCs that
       * are currently running on hardware.
       */

      p = td->td_proc;
      pp = pmc_find_process_descriptor(p, PMC_FLAG_NONE);

      /*
       * save PMCs
       */

      critical_enter();

      cpu = PCPU_GET(cpuid); /* td->td_oncpu is invalid */

      PMCDBG(CSW,SWO,1, "cpu=%d proc=%p (%d, %s) pp=%p", cpu, p,
          p->p_pid, p->p_comm, pp);

      KASSERT(cpu >= 0 && cpu < mp_ncpus,
          ("[pmc,%d wierd CPU id %d", __LINE__, cpu));

      pc = pmc_pcpu[cpu];

      /*
       * When a PMC gets unlinked from a target PMC, it will
       * be removed from the target's pp_pmc[] array.
       *
       * However, on a MP system, the target could have been
       * executing on another CPU at the time of the unlink.
       * So, at context switch OUT time, we need to look at
       * the hardware to determine if a PMC is scheduled on
       * it.
       */

      for (ri = 0; ri < md->pmd_npmc; ri++) {

            pm = NULL;
            (void) (*md->pmd_get_config)(cpu, ri, &pm);

            if (pm == NULL)   /* nothing at this row index */
                  continue;

            mode = PMC_TO_MODE(pm);
            if (!PMC_IS_VIRTUAL_MODE(mode))
                  continue; /* not a process virtual PMC */

            KASSERT(PMC_TO_ROWINDEX(pm) == ri,
                ("[pmc,%d] ri mismatch pmc(%d) ri(%d)",
                  __LINE__, PMC_TO_ROWINDEX(pm), ri));

            /* Stop hardware if not already stopped */
            if (pm->pm_stalled == 0)
                  md->pmd_stop_pmc(cpu, ri);

            /* reduce this PMC's runcount */
            atomic_subtract_rel_32(&pm->pm_runcount, 1);

            /*
             * If this PMC is associated with this process,
             * save the reading.
             */

            if (pp != NULL && pp->pp_pmcs[ri].pp_pmc != NULL) {

                  KASSERT(pm == pp->pp_pmcs[ri].pp_pmc,
                      ("[pmc,%d] pm %p != pp_pmcs[%d] %p", __LINE__,
                        pm, ri, pp->pp_pmcs[ri].pp_pmc));

                  KASSERT(pp->pp_refcnt > 0,
                      ("[pmc,%d] pp refcnt = %d", __LINE__,
                        pp->pp_refcnt));

                  md->pmd_read_pmc(cpu, ri, &newvalue);

                  tmp = newvalue - PMC_PCPU_SAVED(cpu,ri);

                  PMCDBG(CSW,SWI,1,"cpu=%d ri=%d tmp=%jd", cpu, ri,
                      tmp);

                  if (mode == PMC_MODE_TS) {

                        /*
                         * For sampling process-virtual PMCs,
                         * we expect the count to be
                         * decreasing as the 'value'
                         * programmed into the PMC is the
                         * number of events to be seen till
                         * the next sampling interrupt.
                         */
                        if (tmp < 0)
                              tmp += pm->pm_sc.pm_reloadcount;
                        mtx_pool_lock_spin(pmc_mtxpool, pm);
                        pp->pp_pmcs[ri].pp_pmcval -= tmp;
                        if ((int64_t) pp->pp_pmcs[ri].pp_pmcval < 0)
                              pp->pp_pmcs[ri].pp_pmcval +=
                                  pm->pm_sc.pm_reloadcount;
                        mtx_pool_unlock_spin(pmc_mtxpool, pm);

                  } else {

                        /*
                         * For counting process-virtual PMCs,
                         * we expect the count to be
                         * increasing monotonically, modulo a 64
                         * bit wraparound.
                         */
                        KASSERT((int64_t) tmp >= 0,
                            ("[pmc,%d] negative increment cpu=%d "
                             "ri=%d newvalue=%jx saved=%jx "
                             "incr=%jx", __LINE__, cpu, ri,
                             newvalue, PMC_PCPU_SAVED(cpu,ri), tmp));

                        mtx_pool_lock_spin(pmc_mtxpool, pm);
                        pm->pm_gv.pm_savedvalue += tmp;
                        pp->pp_pmcs[ri].pp_pmcval += tmp;
                        mtx_pool_unlock_spin(pmc_mtxpool, pm);

                        if (pm->pm_flags & PMC_F_LOG_PROCCSW)
                              pmclog_process_proccsw(pm, pp, tmp);
                  }
            }

            /* mark hardware as free */
            md->pmd_config_pmc(cpu, ri, NULL);
      }

      /*
       * perform any other architecture/cpu dependent thread
       * switch out functions.
       */

      (void) (*md->pmd_switch_out)(pc, pp);

      critical_exit();
}

/*
 * Log a KLD operation.
 */

static void
pmc_process_kld_load(struct pmckern_map_in *pkm)
{
      struct pmc_owner *po;

      sx_assert(&pmc_sx, SX_LOCKED);

      /*
       * Notify owners of system sampling PMCs about KLD operations.
       */

      LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
          if (po->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_process_map_in(po, (pid_t) -1, pkm->pm_address,
                (char *) pkm->pm_file);

      /*
       * TODO: Notify owners of (all) process-sampling PMCs too.
       */

      return;
}

static void
pmc_process_kld_unload(struct pmckern_map_out *pkm)
{
      struct pmc_owner *po;

      sx_assert(&pmc_sx, SX_LOCKED);

      LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
          if (po->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_process_map_out(po, (pid_t) -1,
                pkm->pm_address, pkm->pm_address + pkm->pm_size);
                
      /*
       * TODO: Notify owners of process-sampling PMCs.
       */
}

/*
 * A mapping change for a process.
 */

static void
pmc_process_mmap(struct thread *td, struct pmckern_map_in *pkm)
{
      int ri;
      pid_t pid;
      char *fullpath, *freepath;
      const struct pmc *pm;
      struct pmc_owner *po;
      const struct pmc_process *pp;

      freepath = fullpath = NULL;
      pmc_getfilename((struct vnode *) pkm->pm_file, &fullpath, &freepath);

      pid = td->td_proc->p_pid;

      /* Inform owners of all system-wide sampling PMCs. */
      LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
          if (po->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_process_map_in(po, pid, pkm->pm_address, fullpath);

      if ((pp = pmc_find_process_descriptor(td->td_proc, 0)) == NULL)
            goto done;

      /*
       * Inform sampling PMC owners tracking this process.
       */
      for (ri = 0; ri < md->pmd_npmc; ri++)
            if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL &&
                PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                  pmclog_process_map_in(pm->pm_owner,
                      pid, pkm->pm_address, fullpath);

  done:
      if (freepath)
            FREE(freepath, M_TEMP);
}


/*
 * Log an munmap request.
 */

static void
pmc_process_munmap(struct thread *td, struct pmckern_map_out *pkm)
{
      int ri;
      pid_t pid;
      struct pmc_owner *po;
      const struct pmc *pm;
      const struct pmc_process *pp;

      pid = td->td_proc->p_pid;

      LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
          if (po->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_process_map_out(po, pid, pkm->pm_address,
                pkm->pm_address + pkm->pm_size);

      if ((pp = pmc_find_process_descriptor(td->td_proc, 0)) == NULL)
            return;

      for (ri = 0; ri < md->pmd_npmc; ri++)
            if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL &&
                PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                  pmclog_process_map_out(pm->pm_owner, pid,
                      pkm->pm_address, pkm->pm_address + pkm->pm_size);
}

/*
 * The 'hook' invoked from the kernel proper
 */


#ifdef      DEBUG
const char *pmc_hooknames[] = {
      /* these strings correspond to PMC_FN_* in <sys/pmckern.h> */
      "",
      "EXEC",
      "CSW-IN",
      "CSW-OUT",
      "SAMPLE",
      "KLDLOAD",
      "KLDUNLOAD",
      "MMAP",
      "MUNMAP"
};
#endif

static int
pmc_hook_handler(struct thread *td, int function, void *arg)
{

      PMCDBG(MOD,PMH,1, "hook td=%p func=%d \"%s\" arg=%p", td, function,
          pmc_hooknames[function], arg);

      switch (function)
      {

      /*
       * Process exec()
       */

      case PMC_FN_PROCESS_EXEC:
      {
            char *fullpath, *freepath;
            unsigned int ri;
            int is_using_hwpmcs;
            struct pmc *pm;
            struct proc *p;
            struct pmc_owner *po;
            struct pmc_process *pp;
            struct pmckern_procexec *pk;

            sx_assert(&pmc_sx, SX_XLOCKED);

            p = td->td_proc;
            pmc_getfilename(p->p_textvp, &fullpath, &freepath);

            pk = (struct pmckern_procexec *) arg;

            /* Inform owners of SS mode PMCs of the exec event. */
            LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
                if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                      pmclog_process_procexec(po, PMC_ID_INVALID,
                        p->p_pid, pk->pm_entryaddr, fullpath);

            PROC_LOCK(p);
            is_using_hwpmcs = p->p_flag & P_HWPMC;
            PROC_UNLOCK(p);

            if (!is_using_hwpmcs) {
                  if (freepath)
                        FREE(freepath, M_TEMP);
                  break;
            }

            /*
             * PMCs are not inherited across an exec():  remove any
             * PMCs that this process is the owner of.
             */

            if ((po = pmc_find_owner_descriptor(p)) != NULL) {
                  pmc_remove_owner(po);
                  pmc_destroy_owner_descriptor(po);
            }

            /*
             * If the process being exec'ed is not the target of any
             * PMC, we are done.
             */
            if ((pp = pmc_find_process_descriptor(p, 0)) == NULL) {
                  if (freepath)
                        FREE(freepath, M_TEMP);
                  break;
            }

            /*
             * Log the exec event to all monitoring owners.  Skip
             * owners who have already recieved the event because
             * they had system sampling PMCs active.
             */
            for (ri = 0; ri < md->pmd_npmc; ri++)
                  if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL) {
                        po = pm->pm_owner;
                        if (po->po_sscount == 0 &&
                            po->po_flags & PMC_PO_OWNS_LOGFILE)
                              pmclog_process_procexec(po, pm->pm_id,
                                  p->p_pid, pk->pm_entryaddr,
                                  fullpath);
                  }

            if (freepath)
                  FREE(freepath, M_TEMP);


            PMCDBG(PRC,EXC,1, "exec proc=%p (%d, %s) cred-changed=%d",
                p, p->p_pid, p->p_comm, pk->pm_credentialschanged);

            if (pk->pm_credentialschanged == 0) /* no change */
                  break;

            /*
             * If the newly exec()'ed process has a different credential
             * than before, allow it to be the target of a PMC only if
             * the PMC's owner has sufficient priviledge.
             */

            for (ri = 0; ri < md->pmd_npmc; ri++)
                  if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL)
                        if (pmc_can_attach(pm, td->td_proc) != 0)
                              pmc_detach_one_process(td->td_proc,
                                  pm, PMC_FLAG_NONE);

            KASSERT(pp->pp_refcnt >= 0 && pp->pp_refcnt < (int) md->pmd_npmc,
                ("[pmc,%d] Illegal ref count %d on pp %p", __LINE__,
                  pp->pp_refcnt, pp));

            /*
             * If this process is no longer the target of any
             * PMCs, we can remove the process entry and free
             * up space.
             */

            if (pp->pp_refcnt == 0) {
                  pmc_remove_process_descriptor(pp);
                  FREE(pp, M_PMC);
                  break;
            }

      }
      break;

      case PMC_FN_CSW_IN:
            pmc_process_csw_in(td);
            break;

      case PMC_FN_CSW_OUT:
            pmc_process_csw_out(td);
            break;

      /*
       * Process accumulated PC samples.
       *
       * This function is expected to be called by hardclock() for
       * each CPU that has accumulated PC samples.
       *
       * This function is to be executed on the CPU whose samples
       * are being processed.
       */
      case PMC_FN_DO_SAMPLES:

            /*
             * Clear the cpu specific bit in the CPU mask before
             * do the rest of the processing.  If the NMI handler
             * gets invoked after the "atomic_clear_int()" call
             * below but before "pmc_process_samples()" gets
             * around to processing the interrupt, then we will
             * come back here at the next hardclock() tick (and
             * may find nothing to do if "pmc_process_samples()"
             * had already processed the interrupt).  We don't
             * lose the interrupt sample.
             */
            atomic_clear_int(&pmc_cpumask, (1 << PCPU_GET(cpuid)));
            pmc_process_samples(PCPU_GET(cpuid));
            break;


      case PMC_FN_KLD_LOAD:
            sx_assert(&pmc_sx, SX_LOCKED);
            pmc_process_kld_load((struct pmckern_map_in *) arg);
            break;

      case PMC_FN_KLD_UNLOAD:
            sx_assert(&pmc_sx, SX_LOCKED);
            pmc_process_kld_unload((struct pmckern_map_out *) arg);
            break;

      case PMC_FN_MMAP:
            sx_assert(&pmc_sx, SX_LOCKED);
            pmc_process_mmap(td, (struct pmckern_map_in *) arg);
            break;

      case PMC_FN_MUNMAP:
            sx_assert(&pmc_sx, SX_LOCKED);
            pmc_process_munmap(td, (struct pmckern_map_out *) arg);
            break;

      default:
#ifdef      DEBUG
            KASSERT(0, ("[pmc,%d] unknown hook %d\n", __LINE__, function));
#endif
            break;

      }

      return 0;
}

/*
 * allocate a 'struct pmc_owner' descriptor in the owner hash table.
 */

static struct pmc_owner *
pmc_allocate_owner_descriptor(struct proc *p)
{
      uint32_t hindex;
      struct pmc_owner *po;
      struct pmc_ownerhash *poh;

      hindex = PMC_HASH_PTR(p, pmc_ownerhashmask);
      poh = &pmc_ownerhash[hindex];

      /* allocate space for N pointers and one descriptor struct */
      MALLOC(po, struct pmc_owner *, sizeof(struct pmc_owner),
          M_PMC, M_ZERO|M_WAITOK);

      po->po_sscount = po->po_error = po->po_flags = 0;
      po->po_file  = NULL;
      po->po_owner = p;
      po->po_kthread = NULL;
      LIST_INIT(&po->po_pmcs);
      LIST_INSERT_HEAD(poh, po, po_next); /* insert into hash table */

      TAILQ_INIT(&po->po_logbuffers);
      mtx_init(&po->po_mtx, "pmc-owner-mtx", "pmc-per-proc", MTX_SPIN);

      PMCDBG(OWN,ALL,1, "allocate-owner proc=%p (%d, %s) pmc-owner=%p",
          p, p->p_pid, p->p_comm, po);

      return po;
}

static void
pmc_destroy_owner_descriptor(struct pmc_owner *po)
{

      PMCDBG(OWN,REL,1, "destroy-owner po=%p proc=%p (%d, %s)",
          po, po->po_owner, po->po_owner->p_pid, po->po_owner->p_comm);

      mtx_destroy(&po->po_mtx);
      FREE(po, M_PMC);
}

/*
 * find the descriptor corresponding to process 'p', adding or removing it
 * as specified by 'mode'.
 */

static struct pmc_process *
pmc_find_process_descriptor(struct proc *p, uint32_t mode)
{
      uint32_t hindex;
      struct pmc_process *pp, *ppnew;
      struct pmc_processhash *pph;

      hindex = PMC_HASH_PTR(p, pmc_processhashmask);
      pph = &pmc_processhash[hindex];

      ppnew = NULL;

      /*
       * Pre-allocate memory in the FIND_ALLOCATE case since we
       * cannot call malloc(9) once we hold a spin lock.
       */

      if (mode & PMC_FLAG_ALLOCATE) {
            /* allocate additional space for 'n' pmc pointers */
            MALLOC(ppnew, struct pmc_process *,
                sizeof(struct pmc_process) + md->pmd_npmc *
                sizeof(struct pmc_targetstate), M_PMC, M_ZERO|M_WAITOK);
      }

      mtx_lock_spin(&pmc_processhash_mtx);
      LIST_FOREACH(pp, pph, pp_next)
          if (pp->pp_proc == p)
                break;

      if ((mode & PMC_FLAG_REMOVE) && pp != NULL)
            LIST_REMOVE(pp, pp_next);

      if ((mode & PMC_FLAG_ALLOCATE) && pp == NULL &&
          ppnew != NULL) {
            ppnew->pp_proc = p;
            LIST_INSERT_HEAD(pph, ppnew, pp_next);
            pp = ppnew;
            ppnew = NULL;
      }
      mtx_unlock_spin(&pmc_processhash_mtx);

      if (pp != NULL && ppnew != NULL)
            FREE(ppnew, M_PMC);

      return pp;
}

/*
 * remove a process descriptor from the process hash table.
 */

static void
pmc_remove_process_descriptor(struct pmc_process *pp)
{
      KASSERT(pp->pp_refcnt == 0,
          ("[pmc,%d] Removing process descriptor %p with count %d",
            __LINE__, pp, pp->pp_refcnt));

      mtx_lock_spin(&pmc_processhash_mtx);
      LIST_REMOVE(pp, pp_next);
      mtx_unlock_spin(&pmc_processhash_mtx);
}


/*
 * find an owner descriptor corresponding to proc 'p'
 */

static struct pmc_owner *
pmc_find_owner_descriptor(struct proc *p)
{
      uint32_t hindex;
      struct pmc_owner *po;
      struct pmc_ownerhash *poh;

      hindex = PMC_HASH_PTR(p, pmc_ownerhashmask);
      poh = &pmc_ownerhash[hindex];

      po = NULL;
      LIST_FOREACH(po, poh, po_next)
          if (po->po_owner == p)
                break;

      PMCDBG(OWN,FND,1, "find-owner proc=%p (%d, %s) hindex=0x%x -> "
          "pmc-owner=%p", p, p->p_pid, p->p_comm, hindex, po);

      return po;
}

/*
 * pmc_allocate_pmc_descriptor
 *
 * Allocate a pmc descriptor and initialize its
 * fields.
 */

static struct pmc *
pmc_allocate_pmc_descriptor(void)
{
      struct pmc *pmc;

      MALLOC(pmc, struct pmc *, sizeof(struct pmc), M_PMC, M_ZERO|M_WAITOK);

      if (pmc != NULL) {
            pmc->pm_owner = NULL;
            LIST_INIT(&pmc->pm_targets);
      }

      PMCDBG(PMC,ALL,1, "allocate-pmc -> pmc=%p", pmc);

      return pmc;
}

/*
 * Destroy a pmc descriptor.
 */

static void
pmc_destroy_pmc_descriptor(struct pmc *pm)
{
      (void) pm;

#ifdef      DEBUG
      KASSERT(pm->pm_state == PMC_STATE_DELETED ||
          pm->pm_state == PMC_STATE_FREE,
          ("[pmc,%d] destroying non-deleted PMC", __LINE__));
      KASSERT(LIST_EMPTY(&pm->pm_targets),
          ("[pmc,%d] destroying pmc with targets", __LINE__));
      KASSERT(pm->pm_owner == NULL,
          ("[pmc,%d] destroying pmc attached to an owner", __LINE__));
      KASSERT(pm->pm_runcount == 0,
          ("[pmc,%d] pmc has non-zero run count %d", __LINE__,
            pm->pm_runcount));
#endif
}

static void
pmc_wait_for_pmc_idle(struct pmc *pm)
{
#ifdef      DEBUG
      volatile int maxloop;

      maxloop = 100 * mp_ncpus;
#endif

      /*
       * Loop (with a forced context switch) till the PMC's runcount
       * comes down to zero.
       */
      while (atomic_load_acq_32(&pm->pm_runcount) > 0) {
#ifdef      DEBUG
            maxloop--;
            KASSERT(maxloop > 0,
                ("[pmc,%d] (ri%d, rc%d) waiting too long for "
                  "pmc to be free", __LINE__,
                  PMC_TO_ROWINDEX(pm), pm->pm_runcount));
#endif
            pmc_force_context_switch();
      }
}

/*
 * This function does the following things:
 *
 *  - detaches the PMC from hardware
 *  - unlinks all target threads that were attached to it
 *  - removes the PMC from its owner's list
 *  - destroy's the PMC private mutex
 *
 * Once this function completes, the given pmc pointer can be safely
 * FREE'd by the caller.
 */

static void
pmc_release_pmc_descriptor(struct pmc *pm)
{
      u_int ri, cpu;
      enum pmc_mode mode;
      struct pmc_hw *phw;
      struct pmc_owner *po;
      struct pmc_process *pp;
      struct pmc_target *ptgt, *tmp;
      struct pmc_binding pb;

      sx_assert(&pmc_sx, SX_XLOCKED);

      KASSERT(pm, ("[pmc,%d] null pmc", __LINE__));

      ri   = PMC_TO_ROWINDEX(pm);
      mode = PMC_TO_MODE(pm);

      PMCDBG(PMC,REL,1, "release-pmc pmc=%p ri=%d mode=%d", pm, ri,
          mode);

      /*
       * First, we take the PMC off hardware.
       */
      cpu = 0;
      if (PMC_IS_SYSTEM_MODE(mode)) {

            /*
             * A system mode PMC runs on a specific CPU.  Switch
             * to this CPU and turn hardware off.
             */
            pmc_save_cpu_binding(&pb);

            cpu = PMC_TO_CPU(pm);

            pmc_select_cpu(cpu);

            /* switch off non-stalled CPUs */
            if (pm->pm_state == PMC_STATE_RUNNING &&
                pm->pm_stalled == 0) {

                  phw = pmc_pcpu[cpu]->pc_hwpmcs[ri];

                  KASSERT(phw->phw_pmc == pm,
                      ("[pmc, %d] pmc ptr ri(%d) hw(%p) pm(%p)",
                        __LINE__, ri, phw->phw_pmc, pm));
                  PMCDBG(PMC,REL,2, "stopping cpu=%d ri=%d", cpu, ri);

                  critical_enter();
                  md->pmd_stop_pmc(cpu, ri);
                  critical_exit();
            }

            PMCDBG(PMC,REL,2, "decfg cpu=%d ri=%d", cpu, ri);

            critical_enter();
            md->pmd_config_pmc(cpu, ri, NULL);
            critical_exit();

            /* adjust the global and process count of SS mode PMCs */
            if (mode == PMC_MODE_SS && pm->pm_state == PMC_STATE_RUNNING) {
                  po = pm->pm_owner;
                  po->po_sscount--;
                  if (po->po_sscount == 0) {
                        atomic_subtract_rel_int(&pmc_ss_count, 1);
                        LIST_REMOVE(po, po_ssnext);
                  }
            }

            pm->pm_state = PMC_STATE_DELETED;

            pmc_restore_cpu_binding(&pb);

            /*
             * We could have references to this PMC structure in
             * the per-cpu sample queues.  Wait for the queue to
             * drain.
             */
            pmc_wait_for_pmc_idle(pm);

      } else if (PMC_IS_VIRTUAL_MODE(mode)) {

            /*
             * A virtual PMC could be running on multiple CPUs at
             * a given instant.
             *
             * By marking its state as DELETED, we ensure that
             * this PMC is never further scheduled on hardware.
             *
             * Then we wait till all CPUs are done with this PMC.
             */
            pm->pm_state = PMC_STATE_DELETED;


            /* Wait for the PMCs runcount to come to zero. */
            pmc_wait_for_pmc_idle(pm);

            /*
             * At this point the PMC is off all CPUs and cannot be
             * freshly scheduled onto a CPU.  It is now safe to
             * unlink all targets from this PMC.  If a
             * process-record's refcount falls to zero, we remove
             * it from the hash table.  The module-wide SX lock
             * protects us from races.
             */
            LIST_FOREACH_SAFE(ptgt, &pm->pm_targets, pt_next, tmp) {
                  pp = ptgt->pt_process;
                  pmc_unlink_target_process(pm, pp); /* frees 'ptgt' */

                  PMCDBG(PMC,REL,3, "pp->refcnt=%d", pp->pp_refcnt);

                  /*
                   * If the target process record shows that no
                   * PMCs are attached to it, reclaim its space.
                   */

                  if (pp->pp_refcnt == 0) {
                        pmc_remove_process_descriptor(pp);
                        FREE(pp, M_PMC);
                  }
            }

            cpu = curthread->td_oncpu; /* setup cpu for pmd_release() */

      }

      /*
       * Release any MD resources
       */

      (void) md->pmd_release_pmc(cpu, ri, pm);

      /*
       * Update row disposition
       */

      if (PMC_IS_SYSTEM_MODE(PMC_TO_MODE(pm)))
            PMC_UNMARK_ROW_STANDALONE(ri);
      else
            PMC_UNMARK_ROW_THREAD(ri);

      /* unlink from the owner's list */
      if (pm->pm_owner) {
            LIST_REMOVE(pm, pm_next);
            pm->pm_owner = NULL;
      }

      pmc_destroy_pmc_descriptor(pm);
}

/*
 * Register an owner and a pmc.
 */

static int
pmc_register_owner(struct proc *p, struct pmc *pmc)
{
      struct pmc_owner *po;

      sx_assert(&pmc_sx, SX_XLOCKED);

      if ((po = pmc_find_owner_descriptor(p)) == NULL)
            if ((po = pmc_allocate_owner_descriptor(p)) == NULL)
                  return ENOMEM;

      KASSERT(pmc->pm_owner == NULL,
          ("[pmc,%d] attempting to own an initialized PMC", __LINE__));
      pmc->pm_owner  = po;

      LIST_INSERT_HEAD(&po->po_pmcs, pmc, pm_next);

      PROC_LOCK(p);
      p->p_flag |= P_HWPMC;
      PROC_UNLOCK(p);

      if (po->po_flags & PMC_PO_OWNS_LOGFILE)
            pmclog_process_pmcallocate(pmc);

      PMCDBG(PMC,REG,1, "register-owner pmc-owner=%p pmc=%p",
          po, pmc);

      return 0;
}

/*
 * Return the current row disposition:
 * == 0 => FREE
 *  > 0 => PROCESS MODE
 *  < 0 => SYSTEM MODE
 */

int
pmc_getrowdisp(int ri)
{
      return pmc_pmcdisp[ri];
}

/*
 * Check if a PMC at row index 'ri' can be allocated to the current
 * process.
 *
 * Allocation can fail if:
 *   - the current process is already being profiled by a PMC at index 'ri',
 *     attached to it via OP_PMCATTACH.
 *   - the current process has already allocated a PMC at index 'ri'
 *     via OP_ALLOCATE.
 */

static int
pmc_can_allocate_rowindex(struct proc *p, unsigned int ri, int cpu)
{
      enum pmc_mode mode;
      struct pmc *pm;
      struct pmc_owner *po;
      struct pmc_process *pp;

      PMCDBG(PMC,ALR,1, "can-allocate-rowindex proc=%p (%d, %s) ri=%d "
          "cpu=%d", p, p->p_pid, p->p_comm, ri, cpu);

      /*
       * We shouldn't have already allocated a process-mode PMC at
       * row index 'ri'.
       *
       * We shouldn't have allocated a system-wide PMC on the same
       * CPU and same RI.
       */
      if ((po = pmc_find_owner_descriptor(p)) != NULL)
            LIST_FOREACH(pm, &po->po_pmcs, pm_next) {
                if (PMC_TO_ROWINDEX(pm) == ri) {
                      mode = PMC_TO_MODE(pm);
                      if (PMC_IS_VIRTUAL_MODE(mode))
                            return EEXIST;
                      if (PMC_IS_SYSTEM_MODE(mode) &&
                        (int) PMC_TO_CPU(pm) == cpu)
                            return EEXIST;
                }
              }

      /*
       * We also shouldn't be the target of any PMC at this index
       * since otherwise a PMC_ATTACH to ourselves will fail.
       */
      if ((pp = pmc_find_process_descriptor(p, 0)) != NULL)
            if (pp->pp_pmcs[ri].pp_pmc)
                  return EEXIST;

      PMCDBG(PMC,ALR,2, "can-allocate-rowindex proc=%p (%d, %s) ri=%d ok",
          p, p->p_pid, p->p_comm, ri);

      return 0;
}

/*
 * Check if a given PMC at row index 'ri' can be currently used in
 * mode 'mode'.
 */

static int
pmc_can_allocate_row(int ri, enum pmc_mode mode)
{
      enum pmc_disp     disp;

      sx_assert(&pmc_sx, SX_XLOCKED);

      PMCDBG(PMC,ALR,1, "can-allocate-row ri=%d mode=%d", ri, mode);

      if (PMC_IS_SYSTEM_MODE(mode))
            disp = PMC_DISP_STANDALONE;
      else
            disp = PMC_DISP_THREAD;

      /*
       * check disposition for PMC row 'ri':
       *
       * Expected disposition       Row-disposition         Result
       *
       * STANDALONE                 STANDALONE or FREE      proceed
       * STANDALONE                 THREAD                  fail
       * THREAD               THREAD or FREE          proceed
       * THREAD               STANDALONE        fail
       */

      if (!PMC_ROW_DISP_IS_FREE(ri) &&
          !(disp == PMC_DISP_THREAD && PMC_ROW_DISP_IS_THREAD(ri)) &&
          !(disp == PMC_DISP_STANDALONE && PMC_ROW_DISP_IS_STANDALONE(ri)))
            return EBUSY;

      /*
       * All OK
       */

      PMCDBG(PMC,ALR,2, "can-allocate-row ri=%d mode=%d ok", ri, mode);

      return 0;

}

/*
 * Find a PMC descriptor with user handle 'pmcid' for thread 'td'.
 */

static struct pmc *
pmc_find_pmc_descriptor_in_process(struct pmc_owner *po, pmc_id_t pmcid)
{
      struct pmc *pm;

      KASSERT(PMC_ID_TO_ROWINDEX(pmcid) < md->pmd_npmc,
          ("[pmc,%d] Illegal pmc index %d (max %d)", __LINE__,
            PMC_ID_TO_ROWINDEX(pmcid), md->pmd_npmc));

      LIST_FOREACH(pm, &po->po_pmcs, pm_next)
          if (pm->pm_id == pmcid)
                return pm;

      return NULL;
}

static int
pmc_find_pmc(pmc_id_t pmcid, struct pmc **pmc)
{

      struct pmc *pm;
      struct pmc_owner *po;

      PMCDBG(PMC,FND,1, "find-pmc id=%d", pmcid);

      if ((po = pmc_find_owner_descriptor(curthread->td_proc)) == NULL)
            return ESRCH;

      if ((pm = pmc_find_pmc_descriptor_in_process(po, pmcid)) == NULL)
            return EINVAL;

      PMCDBG(PMC,FND,2, "find-pmc id=%d -> pmc=%p", pmcid, pm);

      *pmc = pm;
      return 0;
}

/*
 * Start a PMC.
 */

static int
pmc_start(struct pmc *pm)
{
      int error, cpu, ri;
      enum pmc_mode mode;
      struct pmc_owner *po;
      struct pmc_binding pb;

      KASSERT(pm != NULL,
          ("[pmc,%d] null pm", __LINE__));

      mode = PMC_TO_MODE(pm);
      ri   = PMC_TO_ROWINDEX(pm);
      error = 0;

      PMCDBG(PMC,OPS,1, "start pmc=%p mode=%d ri=%d", pm, mode, ri);

      po = pm->pm_owner;

      if (PMC_IS_VIRTUAL_MODE(mode)) {

            /*
             * If a PMCATTACH has never been done on this PMC,
             * attach it to its owner process.
             */

            if (LIST_EMPTY(&pm->pm_targets))
                  error = (pm->pm_flags & PMC_F_ATTACH_DONE) ? ESRCH :
                      pmc_attach_process(po->po_owner, pm);

            /*
             * Disallow PMCSTART if a logfile is required but has not
             * been configured yet.
             */

            if (error == 0 && (pm->pm_flags & PMC_F_NEEDS_LOGFILE) &&
                (po->po_flags & PMC_PO_OWNS_LOGFILE) == 0)
                  error = EDOOFUS;

            /*
             * If the PMC is attached to its owner, then force a context
             * switch to ensure that the MD state gets set correctly.
             */

            if (error == 0) {
                  pm->pm_state = PMC_STATE_RUNNING;
                  if (pm->pm_flags & PMC_F_ATTACHED_TO_OWNER)
                        pmc_force_context_switch();
            }

            return error;
      }


      /*
       * A system-wide PMC.
       */

      if ((pm->pm_flags & PMC_F_NEEDS_LOGFILE) &&
          (po->po_flags & PMC_PO_OWNS_LOGFILE) == 0)
            return EDOOFUS;   /* programming error */

      /*
       * Add the owner to the global list if this is a system-wide
       * sampling PMC.
       */

      if (mode == PMC_MODE_SS) {
            if (po->po_sscount == 0) {
                  LIST_INSERT_HEAD(&pmc_ss_owners, po, po_ssnext);
                  atomic_add_rel_int(&pmc_ss_count, 1);
                  PMCDBG(PMC,OPS,1, "po=%p in global list", po);
            }
            po->po_sscount++;
      }

      /* TODO: dump system wide process mappings to the log? */

      /*
       * Move to the CPU associated with this
       * PMC, and start the hardware.
       */

      pmc_save_cpu_binding(&pb);

      cpu = PMC_TO_CPU(pm);

      if (pmc_cpu_is_disabled(cpu))
            return ENXIO;

      pmc_select_cpu(cpu);

      /*
       * global PMCs are configured at allocation time
       * so write out the initial value and start the PMC.
       */

      pm->pm_state = PMC_STATE_RUNNING;

      critical_enter();
      if ((error = md->pmd_write_pmc(cpu, ri,
             PMC_IS_SAMPLING_MODE(mode) ?
             pm->pm_sc.pm_reloadcount :
             pm->pm_sc.pm_initial)) == 0)
            error = md->pmd_start_pmc(cpu, ri);
      critical_exit();

      pmc_restore_cpu_binding(&pb);

      return error;
}

/*
 * Stop a PMC.
 */

static int
pmc_stop(struct pmc *pm)
{
      int cpu, error, ri;
      struct pmc_owner *po;
      struct pmc_binding pb;

      KASSERT(pm != NULL, ("[pmc,%d] null pmc", __LINE__));

      PMCDBG(PMC,OPS,1, "stop pmc=%p mode=%d ri=%d", pm,
          PMC_TO_MODE(pm), PMC_TO_ROWINDEX(pm));

      pm->pm_state = PMC_STATE_STOPPED;

      /*
       * If the PMC is a virtual mode one, changing the state to
       * non-RUNNING is enough to ensure that the PMC never gets
       * scheduled.
       *
       * If this PMC is current running on a CPU, then it will
       * handled correctly at the time its target process is context
       * switched out.
       */

      if (PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)))
            return 0;

      /*
       * A system-mode PMC.  Move to the CPU associated with
       * this PMC, and stop the hardware.  We update the
       * 'initial count' so that a subsequent PMCSTART will
       * resume counting from the current hardware count.
       */

      pmc_save_cpu_binding(&pb);

      cpu = PMC_TO_CPU(pm);

      KASSERT(cpu >= 0 && cpu < mp_ncpus,
          ("[pmc,%d] illegal cpu=%d", __LINE__, cpu));

      if (pmc_cpu_is_disabled(cpu))
            return ENXIO;

      pmc_select_cpu(cpu);

      ri = PMC_TO_ROWINDEX(pm);

      critical_enter();
      if ((error = md->pmd_stop_pmc(cpu, ri)) == 0)
            error = md->pmd_read_pmc(cpu, ri, &pm->pm_sc.pm_initial);
      critical_exit();

      pmc_restore_cpu_binding(&pb);

      po = pm->pm_owner;

      /* remove this owner from the global list of SS PMC owners */
      if (PMC_TO_MODE(pm) == PMC_MODE_SS) {
            po->po_sscount--;
            if (po->po_sscount == 0) {
                  atomic_subtract_rel_int(&pmc_ss_count, 1);
                  LIST_REMOVE(po, po_ssnext);
                  PMCDBG(PMC,OPS,2,"po=%p removed from global list", po);
            }
      }

      return error;
}


#ifdef      DEBUG
static const char *pmc_op_to_name[] = {
#undef      __PMC_OP
#define     __PMC_OP(N, D)    #N ,
      __PMC_OPS()
      NULL
};
#endif

/*
 * The syscall interface
 */

#define     PMC_GET_SX_XLOCK(...) do {          \
      sx_xlock(&pmc_sx);                  \
      if (pmc_hook == NULL) {             \
            sx_xunlock(&pmc_sx);          \
            return __VA_ARGS__;           \
      }                             \
} while (0)

#define     PMC_DOWNGRADE_SX() do {             \
      sx_downgrade(&pmc_sx);              \
      is_sx_downgraded = 1;               \
} while (0)

static int
pmc_syscall_handler(struct thread *td, void *syscall_args)
{
      int error, is_sx_downgraded, op;
      struct pmc_syscall_args *c;
      void *arg;

      PMC_GET_SX_XLOCK(ENOSYS);

      DROP_GIANT();

      is_sx_downgraded = 0;

      c = (struct pmc_syscall_args *) syscall_args;

      op = c->pmop_code;
      arg = c->pmop_data;

      PMCDBG(MOD,PMS,1, "syscall op=%d \"%s\" arg=%p", op,
          pmc_op_to_name[op], arg);

      error = 0;
      atomic_add_int(&pmc_stats.pm_syscalls, 1);

      switch(op)
      {


      /*
       * Configure a log file.
       *
       * XXX This OP will be reworked.
       */

      case PMC_OP_CONFIGURELOG:
      {
            struct proc *p;
            struct pmc *pm;
            struct pmc_owner *po;
            struct pmckern_map_in *km, *kmbase;
            struct pmc_op_configurelog cl;

            sx_assert(&pmc_sx, SX_XLOCKED);

            if ((error = copyin(arg, &cl, sizeof(cl))) != 0)
                  break;

            /* mark this process as owning a log file */
            p = td->td_proc;
            if ((po = pmc_find_owner_descriptor(p)) == NULL)
                  if ((po = pmc_allocate_owner_descriptor(p)) == NULL) {
                        error = ENOMEM;
                        break;
                  }

            /*
             * If a valid fd was passed in, try to configure that,
             * otherwise if 'fd' was less than zero and there was
             * a log file configured, flush its buffers and
             * de-configure it.
             */
            if (cl.pm_logfd >= 0)
                  error = pmclog_configure_log(po, cl.pm_logfd);
            else if (po->po_flags & PMC_PO_OWNS_LOGFILE) {
                  pmclog_process_closelog(po);
                  error = pmclog_flush(po);
                  if (error == 0) {
                        LIST_FOREACH(pm, &po->po_pmcs, pm_next)
                            if (pm->pm_flags & PMC_F_NEEDS_LOGFILE &&
                              pm->pm_state == PMC_STATE_RUNNING)
                                  pmc_stop(pm);
                        error = pmclog_deconfigure_log(po);
                  }
            } else
                  error = EINVAL;

            if (error)
                  break;

            /*
             * Log the current set of kernel modules.
             */
            kmbase = linker_hwpmc_list_objects();
            for (km = kmbase; km->pm_file != NULL; km++) {
                  PMCDBG(LOG,REG,1,"%s %p", (char *) km->pm_file,
                      (void *) km->pm_address);
                  pmclog_process_map_in(po, (pid_t) -1, km->pm_address,
                      km->pm_file);
            }
            FREE(kmbase, M_LINKER);
      }
      break;


      /*
       * Flush a log file.
       */

      case PMC_OP_FLUSHLOG:
      {
            struct pmc_owner *po;

            sx_assert(&pmc_sx, SX_XLOCKED);

            if ((po = pmc_find_owner_descriptor(td->td_proc)) == NULL) {
                  error = EINVAL;
                  break;
            }

            error = pmclog_flush(po);
      }
      break;

      /*
       * Retrieve hardware configuration.
       */

      case PMC_OP_GETCPUINFO: /* CPU information */
      {
            struct pmc_op_getcpuinfo gci;

            gci.pm_cputype = md->pmd_cputype;
            gci.pm_ncpu    = mp_ncpus;
            gci.pm_npmc    = md->pmd_npmc;
            gci.pm_nclass  = md->pmd_nclass;
            bcopy(md->pmd_classes, &gci.pm_classes,
                sizeof(gci.pm_classes));
            error = copyout(&gci, arg, sizeof(gci));
      }
      break;


      /*
       * Get module statistics
       */

      case PMC_OP_GETDRIVERSTATS:
      {
            struct pmc_op_getdriverstats gms;

            bcopy(&pmc_stats, &gms, sizeof(gms));
            error = copyout(&gms, arg, sizeof(gms));
      }
      break;


      /*
       * Retrieve module version number
       */

      case PMC_OP_GETMODULEVERSION:
      {
            uint32_t cv, modv;

            /* retrieve the client's idea of the ABI version */
            if ((error = copyin(arg, &cv, sizeof(uint32_t))) != 0)
                  break;
            /* don't service clients newer than our driver */
            modv = PMC_VERSION;
            if ((cv & 0xFFFF0000) > (modv & 0xFFFF0000)) {
                  error = EPROGMISMATCH;
                  break;
            }
            error = copyout(&modv, arg, sizeof(int));
      }
      break;


      /*
       * Retrieve the state of all the PMCs on a given
       * CPU.
       */

      case PMC_OP_GETPMCINFO:
      {
            uint32_t cpu, n, npmc;
            size_t pmcinfo_size;
            struct pmc *pm;
            struct pmc_info *p, *pmcinfo;
            struct pmc_op_getpmcinfo *gpi;
            struct pmc_owner *po;
            struct pmc_binding pb;

            PMC_DOWNGRADE_SX();

            gpi = (struct pmc_op_getpmcinfo *) arg;

            if ((error = copyin(&gpi->pm_cpu, &cpu, sizeof(cpu))) != 0)
                  break;

            if (cpu >= (unsigned int) mp_ncpus) {
                  error = EINVAL;
                  break;
            }

            if (pmc_cpu_is_disabled(cpu)) {
                  error = ENXIO;
                  break;
            }

            /* switch to CPU 'cpu' */
            pmc_save_cpu_binding(&pb);
            pmc_select_cpu(cpu);

            npmc = md->pmd_npmc;

            pmcinfo_size = npmc * sizeof(struct pmc_info);
            MALLOC(pmcinfo, struct pmc_info *, pmcinfo_size, M_PMC,
                M_WAITOK);

            p = pmcinfo;

            for (n = 0; n < md->pmd_npmc; n++, p++) {

                  if ((error = md->pmd_describe(cpu, n, p, &pm)) != 0)
                        break;

                  if (PMC_ROW_DISP_IS_STANDALONE(n))
                        p->pm_rowdisp = PMC_DISP_STANDALONE;
                  else if (PMC_ROW_DISP_IS_THREAD(n))
                        p->pm_rowdisp = PMC_DISP_THREAD;
                  else
                        p->pm_rowdisp = PMC_DISP_FREE;

                  p->pm_ownerpid = -1;

                  if (pm == NULL)   /* no PMC associated */
                        continue;

                  po = pm->pm_owner;

                  KASSERT(po->po_owner != NULL,
                      ("[pmc,%d] pmc_owner had a null proc pointer",
                        __LINE__));

                  p->pm_ownerpid = po->po_owner->p_pid;
                  p->pm_mode     = PMC_TO_MODE(pm);
                  p->pm_event    = pm->pm_event;
                  p->pm_flags    = pm->pm_flags;

                  if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                        p->pm_reloadcount =
                            pm->pm_sc.pm_reloadcount;
            }

            pmc_restore_cpu_binding(&pb);

            /* now copy out the PMC info collected */
            if (error == 0)
                  error = copyout(pmcinfo, &gpi->pm_pmcs, pmcinfo_size);

            FREE(pmcinfo, M_PMC);
      }
      break;


      /*
       * Set the administrative state of a PMC.  I.e. whether
       * the PMC is to be used or not.
       */

      case PMC_OP_PMCADMIN:
      {
            int cpu, ri;
            enum pmc_state request;
            struct pmc_cpu *pc;
            struct pmc_hw *phw;
            struct pmc_op_pmcadmin pma;
            struct pmc_binding pb;

            sx_assert(&pmc_sx, SX_XLOCKED);

            KASSERT(td == curthread,
                ("[pmc,%d] td != curthread", __LINE__));

            error = priv_check(td, PRIV_PMC_MANAGE);
            if (error)
                  break;

            if ((error = copyin(arg, &pma, sizeof(pma))) != 0)
                  break;

            cpu = pma.pm_cpu;

            if (cpu < 0 || cpu >= mp_ncpus) {
                  error = EINVAL;
                  break;
            }

            if (pmc_cpu_is_disabled(cpu)) {
                  error = ENXIO;
                  break;
            }

            request = pma.pm_state;

            if (request != PMC_STATE_DISABLED &&
                request != PMC_STATE_FREE) {
                  error = EINVAL;
                  break;
            }

            ri = pma.pm_pmc; /* pmc id == row index */
            if (ri < 0 || ri >= (int) md->pmd_npmc) {
                  error = EINVAL;
                  break;
            }

            /*
             * We can't disable a PMC with a row-index allocated
             * for process virtual PMCs.
             */

            if (PMC_ROW_DISP_IS_THREAD(ri) &&
                request == PMC_STATE_DISABLED) {
                  error = EBUSY;
                  break;
            }

            /*
             * otherwise, this PMC on this CPU is either free or
             * in system-wide mode.
             */

            pmc_save_cpu_binding(&pb);
            pmc_select_cpu(cpu);

            pc  = pmc_pcpu[cpu];
            phw = pc->pc_hwpmcs[ri];

            /*
             * XXX do we need some kind of 'forced' disable?
             */

            if (phw->phw_pmc == NULL) {
                  if (request == PMC_STATE_DISABLED &&
                      (phw->phw_state & PMC_PHW_FLAG_IS_ENABLED)) {
                        phw->phw_state &= ~PMC_PHW_FLAG_IS_ENABLED;
                        PMC_MARK_ROW_STANDALONE(ri);
                  } else if (request == PMC_STATE_FREE &&
                      (phw->phw_state & PMC_PHW_FLAG_IS_ENABLED) == 0) {
                        phw->phw_state |=  PMC_PHW_FLAG_IS_ENABLED;
                        PMC_UNMARK_ROW_STANDALONE(ri);
                  }
                  /* other cases are a no-op */
            } else
                  error = EBUSY;

            pmc_restore_cpu_binding(&pb);
      }
      break;


      /*
       * Allocate a PMC.
       */

      case PMC_OP_PMCALLOCATE:
      {
            uint32_t caps;
            u_int cpu;
            int n;
            enum pmc_mode mode;
            struct pmc *pmc;
            struct pmc_hw *phw;
            struct pmc_op_pmcallocate pa;
            struct pmc_binding pb;

            if ((error = copyin(arg, &pa, sizeof(pa))) != 0)
                  break;

            caps = pa.pm_caps;
            mode = pa.pm_mode;
            cpu  = pa.pm_cpu;

            if ((mode != PMC_MODE_SS  &&  mode != PMC_MODE_SC  &&
                 mode != PMC_MODE_TS  &&  mode != PMC_MODE_TC) ||
                (cpu != (u_int) PMC_CPU_ANY && cpu >= (u_int) mp_ncpus)) {
                  error = EINVAL;
                  break;
            }

            /*
             * Virtual PMCs should only ask for a default CPU.
             * System mode PMCs need to specify a non-default CPU.
             */

            if ((PMC_IS_VIRTUAL_MODE(mode) && cpu != (u_int) PMC_CPU_ANY) ||
                (PMC_IS_SYSTEM_MODE(mode) && cpu == (u_int) PMC_CPU_ANY)) {
                  error = EINVAL;
                  break;
            }

            /*
             * Check that a disabled CPU is not being asked for.
             */

            if (PMC_IS_SYSTEM_MODE(mode) && pmc_cpu_is_disabled(cpu)) {
                  error = ENXIO;
                  break;
            }

            /*
             * Refuse an allocation for a system-wide PMC if this
             * process has been jailed, or if this process lacks
             * super-user credentials and the sysctl tunable
             * 'security.bsd.unprivileged_syspmcs' is zero.
             */

            if (PMC_IS_SYSTEM_MODE(mode)) {
                  if (jailed(curthread->td_ucred)) {
                        error = EPERM;
                        break;
                  }
                  if (!pmc_unprivileged_syspmcs) {
                        error = priv_check(curthread,
                            PRIV_PMC_SYSTEM);
                        if (error)
                              break;
                  }
            }

            if (error)
                  break;

            /*
             * Look for valid values for 'pm_flags'
             */

            if ((pa.pm_flags & ~(PMC_F_DESCENDANTS | PMC_F_LOG_PROCCSW |
                PMC_F_LOG_PROCEXIT)) != 0) {
                  error = EINVAL;
                  break;
            }

            /* process logging options are not allowed for system PMCs */
            if (PMC_IS_SYSTEM_MODE(mode) && (pa.pm_flags &
                (PMC_F_LOG_PROCCSW | PMC_F_LOG_PROCEXIT))) {
                  error = EINVAL;
                  break;
            }

            /*
             * All sampling mode PMCs need to be able to interrupt the
             * CPU.
             */
            if (PMC_IS_SAMPLING_MODE(mode))
                  caps |= PMC_CAP_INTERRUPT;

            /* A valid class specifier should have been passed in. */
            for (n = 0; n < md->pmd_nclass; n++)
                  if (md->pmd_classes[n].pm_class == pa.pm_class)
                        break;
            if (n == md->pmd_nclass) {
                  error = EINVAL;
                  break;
            }

            /* The requested PMC capabilities should be feasible. */
            if ((md->pmd_classes[n].pm_caps & caps) != caps) {
                  error = EOPNOTSUPP;
                  break;
            }

            PMCDBG(PMC,ALL,2, "event=%d caps=0x%x mode=%d cpu=%d",
                pa.pm_ev, caps, mode, cpu);

            pmc = pmc_allocate_pmc_descriptor();
            pmc->pm_id    = PMC_ID_MAKE_ID(cpu,pa.pm_mode,pa.pm_class,
                PMC_ID_INVALID);
            pmc->pm_event = pa.pm_ev;
            pmc->pm_state = PMC_STATE_FREE;
            pmc->pm_caps  = caps;
            pmc->pm_flags = pa.pm_flags;

            /* switch thread to CPU 'cpu' */
            pmc_save_cpu_binding(&pb);

#define     PMC_IS_SHAREABLE_PMC(cpu, n)                    \
      (pmc_pcpu[(cpu)]->pc_hwpmcs[(n)]->phw_state &         \
       PMC_PHW_FLAG_IS_SHAREABLE)
#define     PMC_IS_UNALLOCATED(cpu, n)                      \
      (pmc_pcpu[(cpu)]->pc_hwpmcs[(n)]->phw_pmc == NULL)

            if (PMC_IS_SYSTEM_MODE(mode)) {
                  pmc_select_cpu(cpu);
                  for (n = 0; n < (int) md->pmd_npmc; n++)
                        if (pmc_can_allocate_row(n, mode) == 0 &&
                            pmc_can_allocate_rowindex(
                                  curthread->td_proc, n, cpu) == 0 &&
                            (PMC_IS_UNALLOCATED(cpu, n) ||
                             PMC_IS_SHAREABLE_PMC(cpu, n)) &&
                            md->pmd_allocate_pmc(cpu, n, pmc,
                              &pa) == 0)
                              break;
            } else {
                  /* Process virtual mode */
                  for (n = 0; n < (int) md->pmd_npmc; n++) {
                        if (pmc_can_allocate_row(n, mode) == 0 &&
                            pmc_can_allocate_rowindex(
                                  curthread->td_proc, n,
                                  PMC_CPU_ANY) == 0 &&
                            md->pmd_allocate_pmc(curthread->td_oncpu,
                              n, pmc, &pa) == 0)
                              break;
                  }
            }

#undef      PMC_IS_UNALLOCATED
#undef      PMC_IS_SHAREABLE_PMC

            pmc_restore_cpu_binding(&pb);

            if (n == (int) md->pmd_npmc) {
                  pmc_destroy_pmc_descriptor(pmc);
                  FREE(pmc, M_PMC);
                  pmc = NULL;
                  error = EINVAL;
                  break;
            }

            /* Fill in the correct value in the ID field */
            pmc->pm_id = PMC_ID_MAKE_ID(cpu,mode,pa.pm_class,n);

            PMCDBG(PMC,ALL,2, "ev=%d class=%d mode=%d n=%d -> pmcid=%x",
                pmc->pm_event, pa.pm_class, mode, n, pmc->pm_id);

            /* Process mode PMCs with logging enabled need log files */
            if (pmc->pm_flags & (PMC_F_LOG_PROCEXIT | PMC_F_LOG_PROCCSW))
                  pmc->pm_flags |= PMC_F_NEEDS_LOGFILE;

            /* All system mode sampling PMCs require a log file */
            if (PMC_IS_SAMPLING_MODE(mode) && PMC_IS_SYSTEM_MODE(mode))
                  pmc->pm_flags |= PMC_F_NEEDS_LOGFILE;

            /*
             * Configure global pmc's immediately
             */

            if (PMC_IS_SYSTEM_MODE(PMC_TO_MODE(pmc))) {

                  pmc_save_cpu_binding(&pb);
                  pmc_select_cpu(cpu);

                  phw = pmc_pcpu[cpu]->pc_hwpmcs[n];

                  if ((phw->phw_state & PMC_PHW_FLAG_IS_ENABLED) == 0 ||
                      (error = md->pmd_config_pmc(cpu, n, pmc)) != 0) {
                        (void) md->pmd_release_pmc(cpu, n, pmc);
                        pmc_destroy_pmc_descriptor(pmc);
                        FREE(pmc, M_PMC);
                        pmc = NULL;
                        pmc_restore_cpu_binding(&pb);
                        error = EPERM;
                        break;
                  }

                  pmc_restore_cpu_binding(&pb);
            }

            pmc->pm_state    = PMC_STATE_ALLOCATED;

            /*
             * mark row disposition
             */

            if (PMC_IS_SYSTEM_MODE(mode))
                  PMC_MARK_ROW_STANDALONE(n);
            else
                  PMC_MARK_ROW_THREAD(n);

            /*
             * Register this PMC with the current thread as its owner.
             */

            if ((error =
                pmc_register_owner(curthread->td_proc, pmc)) != 0) {
                  pmc_release_pmc_descriptor(pmc);
                  FREE(pmc, M_PMC);
                  pmc = NULL;
                  break;
            }

            /*
             * Return the allocated index.
             */

            pa.pm_pmcid = pmc->pm_id;

            error = copyout(&pa, arg, sizeof(pa));
      }
      break;


      /*
       * Attach a PMC to a process.
       */

      case PMC_OP_PMCATTACH:
      {
            struct pmc *pm;
            struct proc *p;
            struct pmc_op_pmcattach a;

            sx_assert(&pmc_sx, SX_XLOCKED);

            if ((error = copyin(arg, &a, sizeof(a))) != 0)
                  break;

            if (a.pm_pid < 0) {
                  error = EINVAL;
                  break;
            } else if (a.pm_pid == 0)
                  a.pm_pid = td->td_proc->p_pid;

            if ((error = pmc_find_pmc(a.pm_pmc, &pm)) != 0)
                  break;

            if (PMC_IS_SYSTEM_MODE(PMC_TO_MODE(pm))) {
                  error = EINVAL;
                  break;
            }

            /* PMCs may be (re)attached only when allocated or stopped */
            if (pm->pm_state == PMC_STATE_RUNNING) {
                  error = EBUSY;
                  break;
            } else if (pm->pm_state != PMC_STATE_ALLOCATED &&
                pm->pm_state != PMC_STATE_STOPPED) {
                  error = EINVAL;
                  break;
            }

            /* lookup pid */
            if ((p = pfind(a.pm_pid)) == NULL) {
                  error = ESRCH;
                  break;
            }

            /*
             * Ignore processes that are working on exiting.
             */
            if (p->p_flag & P_WEXIT) {
                  error = ESRCH;
                  PROC_UNLOCK(p);   /* pfind() returns a locked process */
                  break;
            }

            /*
             * we are allowed to attach a PMC to a process if
             * we can debug it.
             */
            error = p_candebug(curthread, p);

            PROC_UNLOCK(p);

            if (error == 0)
                  error = pmc_attach_process(p, pm);
      }
      break;


      /*
       * Detach an attached PMC from a process.
       */

      case PMC_OP_PMCDETACH:
      {
            struct pmc *pm;
            struct proc *p;
            struct pmc_op_pmcattach a;

            if ((error = copyin(arg, &a, sizeof(a))) != 0)
                  break;

            if (a.pm_pid < 0) {
                  error = EINVAL;
                  break;
            } else if (a.pm_pid == 0)
                  a.pm_pid = td->td_proc->p_pid;

            if ((error = pmc_find_pmc(a.pm_pmc, &pm)) != 0)
                  break;

            if ((p = pfind(a.pm_pid)) == NULL) {
                  error = ESRCH;
                  break;
            }

            /*
             * Treat processes that are in the process of exiting
             * as if they were not present.
             */

            if (p->p_flag & P_WEXIT)
                  error = ESRCH;

            PROC_UNLOCK(p);   /* pfind() returns a locked process */

            if (error == 0)
                  error = pmc_detach_process(p, pm);
      }
      break;


      /*
       * Retrieve the MSR number associated with the counter
       * 'pmc_id'.  This allows processes to directly use RDPMC
       * instructions to read their PMCs, without the overhead of a
       * system call.
       */

      case PMC_OP_PMCGETMSR:
      {
            int ri;
            struct pmc  *pm;
            struct pmc_target *pt;
            struct pmc_op_getmsr gm;

            PMC_DOWNGRADE_SX();

            /* CPU has no 'GETMSR' support */
            if (md->pmd_get_msr == NULL) {
                  error = ENOSYS;
                  break;
            }

            if ((error = copyin(arg, &gm, sizeof(gm))) != 0)
                  break;

            if ((error = pmc_find_pmc(gm.pm_pmcid, &pm)) != 0)
                  break;

            /*
             * The allocated PMC has to be a process virtual PMC,
             * i.e., of type MODE_T[CS].  Global PMCs can only be
             * read using the PMCREAD operation since they may be
             * allocated on a different CPU than the one we could
             * be running on at the time of the RDPMC instruction.
             *
             * The GETMSR operation is not allowed for PMCs that
             * are inherited across processes.
             */

            if (!PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)) ||
                (pm->pm_flags & PMC_F_DESCENDANTS)) {
                  error = EINVAL;
                  break;
            }

            /*
             * It only makes sense to use a RDPMC (or its
             * equivalent instruction on non-x86 architectures) on
             * a process that has allocated and attached a PMC to
             * itself.  Conversely the PMC is only allowed to have
             * one process attached to it -- its owner.
             */

            if ((pt = LIST_FIRST(&pm->pm_targets)) == NULL ||
                LIST_NEXT(pt, pt_next) != NULL ||
                pt->pt_process->pp_proc != pm->pm_owner->po_owner) {
                  error = EINVAL;
                  break;
            }

            ri = PMC_TO_ROWINDEX(pm);

            if ((error = (*md->pmd_get_msr)(ri, &gm.pm_msr)) < 0)
                  break;

            if ((error = copyout(&gm, arg, sizeof(gm))) < 0)
                  break;

            /*
             * Mark our process as using MSRs.  Update machine
             * state using a forced context switch.
             */

            pt->pt_process->pp_flags |= PMC_PP_ENABLE_MSR_ACCESS;
            pmc_force_context_switch();

      }
      break;

      /*
       * Release an allocated PMC
       */

      case PMC_OP_PMCRELEASE:
      {
            pmc_id_t pmcid;
            struct pmc *pm;
            struct pmc_owner *po;
            struct pmc_op_simple sp;

            /*
             * Find PMC pointer for the named PMC.
             *
             * Use pmc_release_pmc_descriptor() to switch off the
             * PMC, remove all its target threads, and remove the
             * PMC from its owner's list.
             *
             * Remove the owner record if this is the last PMC
             * owned.
             *
             * Free up space.
             */

            if ((error = copyin(arg, &sp, sizeof(sp))) != 0)
                  break;

            pmcid = sp.pm_pmcid;

            if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
                  break;

            po = pm->pm_owner;
            pmc_release_pmc_descriptor(pm);
            pmc_maybe_remove_owner(po);

            FREE(pm, M_PMC);
      }
      break;


      /*
       * Read and/or write a PMC.
       */

      case PMC_OP_PMCRW:
      {
            uint32_t cpu, ri;
            struct pmc *pm;
            struct pmc_op_pmcrw *pprw;
            struct pmc_op_pmcrw prw;
            struct pmc_binding pb;
            pmc_value_t oldvalue;

            PMC_DOWNGRADE_SX();

            if ((error = copyin(arg, &prw, sizeof(prw))) != 0)
                  break;

            ri = 0;
            PMCDBG(PMC,OPS,1, "rw id=%d flags=0x%x", prw.pm_pmcid,
                prw.pm_flags);

            /* must have at least one flag set */
            if ((prw.pm_flags & (PMC_F_OLDVALUE|PMC_F_NEWVALUE)) == 0) {
                  error = EINVAL;
                  break;
            }

            /* locate pmc descriptor */
            if ((error = pmc_find_pmc(prw.pm_pmcid, &pm)) != 0)
                  break;

            /* Can't read a PMC that hasn't been started. */
            if (pm->pm_state != PMC_STATE_ALLOCATED &&
                pm->pm_state != PMC_STATE_STOPPED &&
                pm->pm_state != PMC_STATE_RUNNING) {
                  error = EINVAL;
                  break;
            }

            /* writing a new value is allowed only for 'STOPPED' pmcs */
            if (pm->pm_state == PMC_STATE_RUNNING &&
                (prw.pm_flags & PMC_F_NEWVALUE)) {
                  error = EBUSY;
                  break;
            }

            if (PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm))) {

                  /*
                   * If this PMC is attached to its owner (i.e.,
                   * the process requesting this operation) and
                   * is running, then attempt to get an
                   * upto-date reading from hardware for a READ.
                   * Writes are only allowed when the PMC is
                   * stopped, so only update the saved value
                   * field.
                   *
                   * If the PMC is not running, or is not
                   * attached to its owner, read/write to the
                   * savedvalue field.
                   */

                  ri = PMC_TO_ROWINDEX(pm);

                  mtx_pool_lock_spin(pmc_mtxpool, pm);
                  cpu = curthread->td_oncpu;

                  if (prw.pm_flags & PMC_F_OLDVALUE) {
                        if ((pm->pm_flags & PMC_F_ATTACHED_TO_OWNER) &&
                            (pm->pm_state == PMC_STATE_RUNNING))
                              error = (*md->pmd_read_pmc)(cpu, ri,
                                  &oldvalue);
                        else
                              oldvalue = pm->pm_gv.pm_savedvalue;
                  }
                  if (prw.pm_flags & PMC_F_NEWVALUE)
                        pm->pm_gv.pm_savedvalue = prw.pm_value;

                  mtx_pool_unlock_spin(pmc_mtxpool, pm);

            } else { /* System mode PMCs */
                  cpu = PMC_TO_CPU(pm);
                  ri  = PMC_TO_ROWINDEX(pm);

                  if (pmc_cpu_is_disabled(cpu)) {
                        error = ENXIO;
                        break;
                  }

                  /* move this thread to CPU 'cpu' */
                  pmc_save_cpu_binding(&pb);
                  pmc_select_cpu(cpu);

                  critical_enter();
                  /* save old value */
                  if (prw.pm_flags & PMC_F_OLDVALUE)
                        if ((error = (*md->pmd_read_pmc)(cpu, ri,
                               &oldvalue)))
                              goto error;
                  /* write out new value */
                  if (prw.pm_flags & PMC_F_NEWVALUE)
                        error = (*md->pmd_write_pmc)(cpu, ri,
                            prw.pm_value);
            error:
                  critical_exit();
                  pmc_restore_cpu_binding(&pb);
                  if (error)
                        break;
            }

            pprw = (struct pmc_op_pmcrw *) arg;

#ifdef      DEBUG
            if (prw.pm_flags & PMC_F_NEWVALUE)
                  PMCDBG(PMC,OPS,2, "rw id=%d new %jx -> old %jx",
                      ri, prw.pm_value, oldvalue);
            else if (prw.pm_flags & PMC_F_OLDVALUE)
                  PMCDBG(PMC,OPS,2, "rw id=%d -> old %jx", ri, oldvalue);
#endif

            /* return old value if requested */
            if (prw.pm_flags & PMC_F_OLDVALUE)
                  if ((error = copyout(&oldvalue, &pprw->pm_value,
                         sizeof(prw.pm_value))))
                        break;

      }
      break;


      /*
       * Set the sampling rate for a sampling mode PMC and the
       * initial count for a counting mode PMC.
       */

      case PMC_OP_PMCSETCOUNT:
      {
            struct pmc *pm;
            struct pmc_op_pmcsetcount sc;

            PMC_DOWNGRADE_SX();

            if ((error = copyin(arg, &sc, sizeof(sc))) != 0)
                  break;

            if ((error = pmc_find_pmc(sc.pm_pmcid, &pm)) != 0)
                  break;

            if (pm->pm_state == PMC_STATE_RUNNING) {
                  error = EBUSY;
                  break;
            }

            if (PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)))
                  pm->pm_sc.pm_reloadcount = sc.pm_count;
            else
                  pm->pm_sc.pm_initial = sc.pm_count;
      }
      break;


      /*
       * Start a PMC.
       */

      case PMC_OP_PMCSTART:
      {
            pmc_id_t pmcid;
            struct pmc *pm;
            struct pmc_op_simple sp;

            sx_assert(&pmc_sx, SX_XLOCKED);

            if ((error = copyin(arg, &sp, sizeof(sp))) != 0)
                  break;

            pmcid = sp.pm_pmcid;

            if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
                  break;

            KASSERT(pmcid == pm->pm_id,
                ("[pmc,%d] pmcid %x != id %x", __LINE__,
                  pm->pm_id, pmcid));

            if (pm->pm_state == PMC_STATE_RUNNING) /* already running */
                  break;
            else if (pm->pm_state != PMC_STATE_STOPPED &&
                pm->pm_state != PMC_STATE_ALLOCATED) {
                  error = EINVAL;
                  break;
            }

            error = pmc_start(pm);
      }
      break;


      /*
       * Stop a PMC.
       */

      case PMC_OP_PMCSTOP:
      {
            pmc_id_t pmcid;
            struct pmc *pm;
            struct pmc_op_simple sp;

            PMC_DOWNGRADE_SX();

            if ((error = copyin(arg, &sp, sizeof(sp))) != 0)
                  break;

            pmcid = sp.pm_pmcid;

            /*
             * Mark the PMC as inactive and invoke the MD stop
             * routines if needed.
             */

            if ((error = pmc_find_pmc(pmcid, &pm)) != 0)
                  break;

            KASSERT(pmcid == pm->pm_id,
                ("[pmc,%d] pmc id %x != pmcid %x", __LINE__,
                  pm->pm_id, pmcid));

            if (pm->pm_state == PMC_STATE_STOPPED) /* already stopped */
                  break;
            else if (pm->pm_state != PMC_STATE_RUNNING) {
                  error = EINVAL;
                  break;
            }

            error = pmc_stop(pm);
      }
      break;


      /*
       * Write a user supplied value to the log file.
       */

      case PMC_OP_WRITELOG:
      {
            struct pmc_op_writelog wl;
            struct pmc_owner *po;

            PMC_DOWNGRADE_SX();

            if ((error = copyin(arg, &wl, sizeof(wl))) != 0)
                  break;

            if ((po = pmc_find_owner_descriptor(td->td_proc)) == NULL) {
                  error = EINVAL;
                  break;
            }

            if ((po->po_flags & PMC_PO_OWNS_LOGFILE) == 0) {
                  error = EINVAL;
                  break;
            }

            error = pmclog_process_userlog(po, &wl);
      }
      break;


      default:
            error = EINVAL;
            break;
      }

      if (is_sx_downgraded)
            sx_sunlock(&pmc_sx);
      else
            sx_xunlock(&pmc_sx);

      if (error)
            atomic_add_int(&pmc_stats.pm_syscall_errors, 1);

      PICKUP_GIANT();

      return error;
}

/*
 * Helper functions
 */


/*
 * Interrupt processing.
 *
 * Find a free slot in the per-cpu array of PC samples and write the
 * current (PMC,PID,PC) triple to it.  If an event was successfully
 * added, a bit is set in mask 'pmc_cpumask' denoting that the
 * DO_SAMPLES hook needs to be invoked from the clock handler.
 *
 * This function is meant to be called from an NMI handler.  It cannot
 * use any of the locking primitives supplied by the OS.
 */

int
pmc_process_interrupt(int cpu, struct pmc *pm, uintfptr_t pc, int usermode)
{
      int error, ri;
      struct thread *td;
      struct pmc_sample *ps;
      struct pmc_samplebuffer *psb;

      error = 0;
      ri = PMC_TO_ROWINDEX(pm);

      psb = pmc_pcpu[cpu]->pc_sb;

      ps = psb->ps_write;
      if (ps->ps_pc) {  /* in use, reader hasn't caught up */
            pm->pm_stalled = 1;
            atomic_add_int(&pmc_stats.pm_intr_bufferfull, 1);
            PMCDBG(SAM,INT,1,"(spc) cpu=%d pm=%p pc=%jx um=%d wr=%d rd=%d",
                cpu, pm, (uint64_t) pc, usermode,
                (int) (psb->ps_write - psb->ps_samples),
                (int) (psb->ps_read - psb->ps_samples));
            error = ENOMEM;
            goto done;
      }

      /* fill in entry */
      PMCDBG(SAM,INT,1,"cpu=%d pm=%p pc=%jx um=%d wr=%d rd=%d", cpu, pm,
          (uint64_t) pc, usermode,
          (int) (psb->ps_write - psb->ps_samples),
          (int) (psb->ps_read - psb->ps_samples));

      atomic_add_rel_32(&pm->pm_runcount, 1);         /* hold onto PMC */
      ps->ps_pmc = pm;
      if ((td = curthread) && td->td_proc)
            ps->ps_pid = td->td_proc->p_pid;
      else
            ps->ps_pid = -1;
      ps->ps_usermode = usermode;
      ps->ps_pc = pc;         /* mark entry as in use */

      /* increment write pointer, modulo ring buffer size */
      ps++;
      if (ps == psb->ps_fence)
            psb->ps_write = psb->ps_samples;
      else
            psb->ps_write = ps;

 done:
      /* mark CPU as needing processing */
      atomic_set_rel_int(&pmc_cpumask, (1 << cpu));

      return error;
}


/*
 * Process saved PC samples.
 */

static void
pmc_process_samples(int cpu)
{
      int n, ri;
      struct pmc *pm;
      struct thread *td;
      struct pmc_owner *po;
      struct pmc_sample *ps;
      struct pmc_samplebuffer *psb;

      KASSERT(PCPU_GET(cpuid) == cpu,
          ("[pmc,%d] not on the correct CPU pcpu=%d cpu=%d", __LINE__,
            PCPU_GET(cpuid), cpu));

      psb = pmc_pcpu[cpu]->pc_sb;

      for (n = 0; n < pmc_nsamples; n++) { /* bound on #iterations */

            ps = psb->ps_read;
            if (ps->ps_pc == (uintfptr_t) 0)    /* no data */
                  break;

            pm = ps->ps_pmc;
            po = pm->pm_owner;

            KASSERT(PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)),
                ("[pmc,%d] pmc=%p non-sampling mode=%d", __LINE__,
                  pm, PMC_TO_MODE(pm)));

            /* Ignore PMCs that have been switched off */
            if (pm->pm_state != PMC_STATE_RUNNING)
                  goto entrydone;

            PMCDBG(SAM,OPS,1,"cpu=%d pm=%p pc=%jx um=%d wr=%d rd=%d", cpu,
                pm, (uint64_t) ps->ps_pc, ps->ps_usermode,
                (int) (psb->ps_write - psb->ps_samples),
                (int) (psb->ps_read - psb->ps_samples));

            /*
             * If this is a process-mode PMC that is attached to
             * its owner, and if the PC is in user mode, update
             * profiling statistics like timer-based profiling
             * would have done.
             */
            if (pm->pm_flags & PMC_F_ATTACHED_TO_OWNER) {
                  if (ps->ps_usermode) {
                        td = FIRST_THREAD_IN_PROC(po->po_owner);
                        addupc_intr(td, ps->ps_pc, 1);
                  }
                  goto entrydone;
            }

            /*
             * Otherwise, this is either a sampling mode PMC that
             * is attached to a different process than its owner,
             * or a system-wide sampling PMC.  Dispatch a log
             * entry to the PMC's owner process.
             */

            pmclog_process_pcsample(pm, ps);

      entrydone:
            ps->ps_pc = (uintfptr_t) 0;   /* mark entry as free */
            atomic_subtract_rel_32(&pm->pm_runcount, 1);

            /* increment read pointer, modulo sample size */
            if (++ps == psb->ps_fence)
                  psb->ps_read = psb->ps_samples;
            else
                  psb->ps_read = ps;
      }

      atomic_add_int(&pmc_stats.pm_log_sweeps, 1);

      /* Do not re-enable stalled PMCs if we failed to process any samples */
      if (n == 0)
            return;

      /*
       * Restart any stalled sampling PMCs on this CPU.
       *
       * If the NMI handler sets the pm_stalled field of a PMC after
       * the check below, we'll end up processing the stalled PMC at
       * the next hardclock tick.
       */
      for (n = 0; n < md->pmd_npmc; n++) {
            (void) (*md->pmd_get_config)(cpu,n,&pm);
            if (pm == NULL ||              /* !cfg'ed */
                pm->pm_state != PMC_STATE_RUNNING || /* !active */
                !PMC_IS_SAMPLING_MODE(PMC_TO_MODE(pm)) || /* !sampling */
                pm->pm_stalled == 0) /* !stalled */
                  continue;

            pm->pm_stalled = 0;
            ri = PMC_TO_ROWINDEX(pm);
            (*md->pmd_start_pmc)(cpu, ri);
      }
}

/*
 * Event handlers.
 */

/*
 * Handle a process exit.
 *
 * Remove this process from all hash tables.  If this process
 * owned any PMCs, turn off those PMCs and deallocate them,
 * removing any associations with target processes.
 *
 * This function will be called by the last 'thread' of a
 * process.
 *
 * XXX This eventhandler gets called early in the exit process.
 * Consider using a 'hook' invocation from thread_exit() or equivalent
 * spot.  Another negative is that kse_exit doesn't seem to call
 * exit1() [??].
 *
 */

static void
pmc_process_exit(void *arg __unused, struct proc *p)
{
      int is_using_hwpmcs;
      int cpu;
      unsigned int ri;
      struct pmc *pm;
      struct pmc_process *pp;
      struct pmc_owner *po;
      pmc_value_t newvalue, tmp;

      PROC_LOCK(p);
      is_using_hwpmcs = p->p_flag & P_HWPMC;
      PROC_UNLOCK(p);

      /*
       * Log a sysexit event to all SS PMC owners.
       */
      LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
          if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_process_sysexit(po, p->p_pid);

      if (!is_using_hwpmcs)
            return;

      PMC_GET_SX_XLOCK();
      PMCDBG(PRC,EXT,1,"process-exit proc=%p (%d, %s)", p, p->p_pid,
          p->p_comm);

      /*
       * Since this code is invoked by the last thread in an exiting
       * process, we would have context switched IN at some prior
       * point.  However, with PREEMPTION, kernel mode context
       * switches may happen any time, so we want to disable a
       * context switch OUT till we get any PMCs targetting this
       * process off the hardware.
       *
       * We also need to atomically remove this process'
       * entry from our target process hash table, using
       * PMC_FLAG_REMOVE.
       */
      PMCDBG(PRC,EXT,1, "process-exit proc=%p (%d, %s)", p, p->p_pid,
          p->p_comm);

      critical_enter(); /* no preemption */

      cpu = curthread->td_oncpu;

      if ((pp = pmc_find_process_descriptor(p,
             PMC_FLAG_REMOVE)) != NULL) {

            PMCDBG(PRC,EXT,2,
                "process-exit proc=%p pmc-process=%p", p, pp);

            /*
             * The exiting process could the target of
             * some PMCs which will be running on
             * currently executing CPU.
             *
             * We need to turn these PMCs off like we
             * would do at context switch OUT time.
             */
            for (ri = 0; ri < md->pmd_npmc; ri++) {

                  /*
                   * Pick up the pmc pointer from hardware
                   * state similar to the CSW_OUT code.
                   */
                  pm = NULL;
                  (void) (*md->pmd_get_config)(cpu, ri, &pm);

                  PMCDBG(PRC,EXT,2, "ri=%d pm=%p", ri, pm);

                  if (pm == NULL ||
                      !PMC_IS_VIRTUAL_MODE(PMC_TO_MODE(pm)))
                        continue;

                  PMCDBG(PRC,EXT,2, "ppmcs[%d]=%p pm=%p "
                      "state=%d", ri, pp->pp_pmcs[ri].pp_pmc,
                      pm, pm->pm_state);

                  KASSERT(PMC_TO_ROWINDEX(pm) == ri,
                      ("[pmc,%d] ri mismatch pmc(%d) ri(%d)",
                        __LINE__, PMC_TO_ROWINDEX(pm), ri));

                  KASSERT(pm == pp->pp_pmcs[ri].pp_pmc,
                      ("[pmc,%d] pm %p != pp_pmcs[%d] %p",
                        __LINE__, pm, ri, pp->pp_pmcs[ri].pp_pmc));

                  (void) md->pmd_stop_pmc(cpu, ri);

                  KASSERT(pm->pm_runcount > 0,
                      ("[pmc,%d] bad runcount ri %d rc %d",
                        __LINE__, ri, pm->pm_runcount));

                  /* Stop hardware only if it is actually running */
                  if (pm->pm_state == PMC_STATE_RUNNING &&
                      pm->pm_stalled == 0) {
                        md->pmd_read_pmc(cpu, ri, &newvalue);
                        tmp = newvalue -
                            PMC_PCPU_SAVED(cpu,ri);

                        mtx_pool_lock_spin(pmc_mtxpool, pm);
                        pm->pm_gv.pm_savedvalue += tmp;
                        pp->pp_pmcs[ri].pp_pmcval += tmp;
                        mtx_pool_unlock_spin(pmc_mtxpool, pm);
                  }

                  atomic_subtract_rel_32(&pm->pm_runcount,1);

                  KASSERT((int) pm->pm_runcount >= 0,
                      ("[pmc,%d] runcount is %d", __LINE__, ri));

                  (void) md->pmd_config_pmc(cpu, ri, NULL);
            }

            /*
             * Inform the MD layer of this pseudo "context switch
             * out"
             */
            (void) md->pmd_switch_out(pmc_pcpu[cpu], pp);

            critical_exit(); /* ok to be pre-empted now */

            /*
             * Unlink this process from the PMCs that are
             * targetting it.  This will send a signal to
             * all PMC owner's whose PMCs are orphaned.
             *
             * Log PMC value at exit time if requested.
             */
            for (ri = 0; ri < md->pmd_npmc; ri++)
                  if ((pm = pp->pp_pmcs[ri].pp_pmc) != NULL) {
                        if (pm->pm_flags & PMC_F_NEEDS_LOGFILE &&
                            PMC_IS_COUNTING_MODE(PMC_TO_MODE(pm)))
                              pmclog_process_procexit(pm, pp);
                        pmc_unlink_target_process(pm, pp);
                  }
            FREE(pp, M_PMC);

      } else
            critical_exit(); /* pp == NULL */


      /*
       * If the process owned PMCs, free them up and free up
       * memory.
       */
      if ((po = pmc_find_owner_descriptor(p)) != NULL) {
            pmc_remove_owner(po);
            pmc_destroy_owner_descriptor(po);
      }

      sx_xunlock(&pmc_sx);
}

/*
 * Handle a process fork.
 *
 * If the parent process 'p1' is under HWPMC monitoring, then copy
 * over any attached PMCs that have 'do_descendants' semantics.
 */

static void
pmc_process_fork(void *arg __unused, struct proc *p1, struct proc *newproc,
    int flags)
{
      int is_using_hwpmcs;
      unsigned int ri;
      uint32_t do_descendants;
      struct pmc *pm;
      struct pmc_owner *po;
      struct pmc_process *ppnew, *ppold;

      (void) flags;           /* unused parameter */

      PROC_LOCK(p1);
      is_using_hwpmcs = p1->p_flag & P_HWPMC;
      PROC_UNLOCK(p1);

      /*
       * If there are system-wide sampling PMCs active, we need to
       * log all fork events to their owner's logs.
       */

      LIST_FOREACH(po, &pmc_ss_owners, po_ssnext)
          if (po->po_flags & PMC_PO_OWNS_LOGFILE)
                pmclog_process_procfork(po, p1->p_pid, newproc->p_pid);

      if (!is_using_hwpmcs)
            return;

      PMC_GET_SX_XLOCK();
      PMCDBG(PMC,FRK,1, "process-fork proc=%p (%d, %s) -> %p", p1,
          p1->p_pid, p1->p_comm, newproc);

      /*
       * If the parent process (curthread->td_proc) is a
       * target of any PMCs, look for PMCs that are to be
       * inherited, and link these into the new process
       * descriptor.
       */
      if ((ppold = pmc_find_process_descriptor(curthread->td_proc,
             PMC_FLAG_NONE)) == NULL)
            goto done;        /* nothing to do */

      do_descendants = 0;
      for (ri = 0; ri < md->pmd_npmc; ri++)
            if ((pm = ppold->pp_pmcs[ri].pp_pmc) != NULL)
                  do_descendants |= pm->pm_flags & PMC_F_DESCENDANTS;
      if (do_descendants == 0) /* nothing to do */
            goto done;

      /* allocate a descriptor for the new process  */
      if ((ppnew = pmc_find_process_descriptor(newproc,
             PMC_FLAG_ALLOCATE)) == NULL)
            goto done;

      /*
       * Run through all PMCs that were targeting the old process
       * and which specified F_DESCENDANTS and attach them to the
       * new process.
       *
       * Log the fork event to all owners of PMCs attached to this
       * process, if not already logged.
       */
      for (ri = 0; ri < md->pmd_npmc; ri++)
            if ((pm = ppold->pp_pmcs[ri].pp_pmc) != NULL &&
                (pm->pm_flags & PMC_F_DESCENDANTS)) {
                  pmc_link_target_process(pm, ppnew);
                  po = pm->pm_owner;
                  if (po->po_sscount == 0 &&
                      po->po_flags & PMC_PO_OWNS_LOGFILE)
                        pmclog_process_procfork(po, p1->p_pid,
                            newproc->p_pid);
            }

      /*
       * Now mark the new process as being tracked by this driver.
       */
      PROC_LOCK(newproc);
      newproc->p_flag |= P_HWPMC;
      PROC_UNLOCK(newproc);

 done:
      sx_xunlock(&pmc_sx);
}


/*
 * initialization
 */

static const char *pmc_name_of_pmcclass[] = {
#undef      __PMC_CLASS
#define     __PMC_CLASS(N) #N ,
      __PMC_CLASSES()
};

static int
pmc_initialize(void)
{
      int cpu, error, n;
      struct pmc_binding pb;
      struct pmc_samplebuffer *sb;

      md = NULL;
      error = 0;

#ifdef      DEBUG
      /* parse debug flags first */
      if (TUNABLE_STR_FETCH(PMC_SYSCTL_NAME_PREFIX "debugflags",
            pmc_debugstr, sizeof(pmc_debugstr)))
            pmc_debugflags_parse(pmc_debugstr,
                pmc_debugstr+strlen(pmc_debugstr));
#endif

      PMCDBG(MOD,INI,0, "PMC Initialize (version %x)", PMC_VERSION);

      /* check kernel version */
      if (pmc_kernel_version != PMC_VERSION) {
            if (pmc_kernel_version == 0)
                  printf("hwpmc: this kernel has not been compiled with "
                      "'options HWPMC_HOOKS'.\n");
            else
                  printf("hwpmc: kernel version (0x%x) does not match "
                      "module version (0x%x).\n", pmc_kernel_version,
                      PMC_VERSION);
            return EPROGMISMATCH;
      }

      /*
       * check sysctl parameters
       */

      if (pmc_hashsize <= 0) {
            (void) printf("hwpmc: tunable hashsize=%d must be greater "
                "than zero.\n", pmc_hashsize);
            pmc_hashsize = PMC_HASH_SIZE;
      }

      if (pmc_nsamples <= 0 || pmc_nsamples > 65535) {
            (void) printf("hwpmc: tunable nsamples=%d out of range.\n",
                pmc_nsamples);
            pmc_nsamples = PMC_NSAMPLES;
      }

      md = pmc_md_initialize();

      if (md == NULL || md->pmd_init == NULL)
            return ENOSYS;

      /* allocate space for the per-cpu array */
      MALLOC(pmc_pcpu, struct pmc_cpu **, mp_ncpus * sizeof(struct pmc_cpu *),
          M_PMC, M_WAITOK|M_ZERO);

      /* per-cpu 'saved values' for managing process-mode PMCs */
      MALLOC(pmc_pcpu_saved, pmc_value_t *,
          sizeof(pmc_value_t) * mp_ncpus * md->pmd_npmc, M_PMC, M_WAITOK);

      /* perform cpu dependent initialization */
      pmc_save_cpu_binding(&pb);
      for (cpu = 0; cpu < mp_ncpus; cpu++) {
            if (pmc_cpu_is_disabled(cpu))
                  continue;
            pmc_select_cpu(cpu);
            if ((error = md->pmd_init(cpu)) != 0)
                  break;
      }
      pmc_restore_cpu_binding(&pb);

      if (error != 0)
            return error;

      /* allocate space for the sample array */
      for (cpu = 0; cpu < mp_ncpus; cpu++) {
            if (pmc_cpu_is_disabled(cpu))
                  continue;
            MALLOC(sb, struct pmc_samplebuffer *,
                sizeof(struct pmc_samplebuffer) +
                pmc_nsamples * sizeof(struct pmc_sample), M_PMC,
                M_WAITOK|M_ZERO);

            sb->ps_read = sb->ps_write = sb->ps_samples;
            sb->ps_fence = sb->ps_samples + pmc_nsamples;
            KASSERT(pmc_pcpu[cpu] != NULL,
                ("[pmc,%d] cpu=%d Null per-cpu data", __LINE__, cpu));

            pmc_pcpu[cpu]->pc_sb = sb;
      }

      /* allocate space for the row disposition array */
      pmc_pmcdisp = malloc(sizeof(enum pmc_mode) * md->pmd_npmc,
          M_PMC, M_WAITOK|M_ZERO);

      KASSERT(pmc_pmcdisp != NULL,
          ("[pmc,%d] pmcdisp allocation returned NULL", __LINE__));

      /* mark all PMCs as available */
      for (n = 0; n < (int) md->pmd_npmc; n++)
            PMC_MARK_ROW_FREE(n);

      /* allocate thread hash tables */
      pmc_ownerhash = hashinit(pmc_hashsize, M_PMC,
          &pmc_ownerhashmask);

      pmc_processhash = hashinit(pmc_hashsize, M_PMC,
          &pmc_processhashmask);
      mtx_init(&pmc_processhash_mtx, "pmc-process-hash", "pmc-leaf",
          MTX_SPIN);

      LIST_INIT(&pmc_ss_owners);
      pmc_ss_count = 0;

      /* allocate a pool of spin mutexes */
      pmc_mtxpool = mtx_pool_create("pmc-leaf", pmc_mtxpool_size,
          MTX_SPIN);

      PMCDBG(MOD,INI,1, "pmc_ownerhash=%p, mask=0x%lx "
          "targethash=%p mask=0x%lx", pmc_ownerhash, pmc_ownerhashmask,
          pmc_processhash, pmc_processhashmask);

      /* register process {exit,fork,exec} handlers */
      pmc_exit_tag = EVENTHANDLER_REGISTER(process_exit,
          pmc_process_exit, NULL, EVENTHANDLER_PRI_ANY);
      pmc_fork_tag = EVENTHANDLER_REGISTER(process_fork,
          pmc_process_fork, NULL, EVENTHANDLER_PRI_ANY);

      /* initialize logging */
      pmclog_initialize();

      /* set hook functions */
      pmc_intr = md->pmd_intr;
      pmc_hook = pmc_hook_handler;

      if (error == 0) {
            printf(PMC_MODULE_NAME ":");
            for (n = 0; n < (int) md->pmd_nclass; n++) {
                  printf(" %s/%d/0x%b",
                      pmc_name_of_pmcclass[md->pmd_classes[n].pm_class],
                      md->pmd_nclasspmcs[n],
                      md->pmd_classes[n].pm_caps,
                      "\20"
                      "\1INT\2USR\3SYS\4EDG\5THR"
                      "\6REA\7WRI\10INV\11QUA\12PRC"
                      "\13TAG\14CSC");
            }
            printf("\n");
      }

      return error;
}

/* prepare to be unloaded */
static void
pmc_cleanup(void)
{
      int cpu;
      struct pmc_ownerhash *ph;
      struct pmc_owner *po, *tmp;
      struct pmc_binding pb;
#ifdef      DEBUG
      struct pmc_processhash *prh;
#endif

      PMCDBG(MOD,INI,0, "%s", "cleanup");

      /* switch off sampling */
      atomic_store_rel_int(&pmc_cpumask, 0);
      pmc_intr = NULL;

      sx_xlock(&pmc_sx);
      if (pmc_hook == NULL) { /* being unloaded already */
            sx_xunlock(&pmc_sx);
            return;
      }

      pmc_hook = NULL; /* prevent new threads from entering module */

      /* deregister event handlers */
      EVENTHANDLER_DEREGISTER(process_fork, pmc_fork_tag);
      EVENTHANDLER_DEREGISTER(process_exit, pmc_exit_tag);

      /* send SIGBUS to all owner threads, free up allocations */
      if (pmc_ownerhash)
            for (ph = pmc_ownerhash;
                 ph <= &pmc_ownerhash[pmc_ownerhashmask];
                 ph++) {
                  LIST_FOREACH_SAFE(po, ph, po_next, tmp) {
                        pmc_remove_owner(po);

                        /* send SIGBUS to owner processes */
                        PMCDBG(MOD,INI,2, "cleanup signal proc=%p "
                            "(%d, %s)", po->po_owner,
                            po->po_owner->p_pid,
                            po->po_owner->p_comm);

                        PROC_LOCK(po->po_owner);
                        psignal(po->po_owner, SIGBUS);
                        PROC_UNLOCK(po->po_owner);

                        pmc_destroy_owner_descriptor(po);
                  }
            }

      /* reclaim allocated data structures */
      if (pmc_mtxpool)
            mtx_pool_destroy(&pmc_mtxpool);

      mtx_destroy(&pmc_processhash_mtx);
      if (pmc_processhash) {
#ifdef      DEBUG
            struct pmc_process *pp;

            PMCDBG(MOD,INI,3, "%s", "destroy process hash");
            for (prh = pmc_processhash;
                 prh <= &pmc_processhash[pmc_processhashmask];
                 prh++)
                  LIST_FOREACH(pp, prh, pp_next)
                      PMCDBG(MOD,INI,3, "pid=%d", pp->pp_proc->p_pid);
#endif

            hashdestroy(pmc_processhash, M_PMC, pmc_processhashmask);
            pmc_processhash = NULL;
      }

      if (pmc_ownerhash) {
            PMCDBG(MOD,INI,3, "%s", "destroy owner hash");
            hashdestroy(pmc_ownerhash, M_PMC, pmc_ownerhashmask);
            pmc_ownerhash = NULL;
      }

      KASSERT(LIST_EMPTY(&pmc_ss_owners),
          ("[pmc,%d] Global SS owner list not empty", __LINE__));
      KASSERT(pmc_ss_count == 0,
          ("[pmc,%d] Global SS count not empty", __LINE__));

      /* free the per-cpu sample buffers */
      for (cpu = 0; cpu < mp_ncpus; cpu++) {
            if (pmc_cpu_is_disabled(cpu))
                  continue;
            KASSERT(pmc_pcpu[cpu]->pc_sb != NULL,
                ("[pmc,%d] Null cpu sample buffer cpu=%d", __LINE__,
                  cpu));
            FREE(pmc_pcpu[cpu]->pc_sb, M_PMC);
            pmc_pcpu[cpu]->pc_sb = NULL;
      }

      /* do processor dependent cleanup */
      PMCDBG(MOD,INI,3, "%s", "md cleanup");
      if (md) {
            pmc_save_cpu_binding(&pb);
            for (cpu = 0; cpu < mp_ncpus; cpu++) {
                  PMCDBG(MOD,INI,1,"pmc-cleanup cpu=%d pcs=%p",
                      cpu, pmc_pcpu[cpu]);
                  if (pmc_cpu_is_disabled(cpu))
                        continue;
                  pmc_select_cpu(cpu);
                  if (pmc_pcpu[cpu])
                        (void) md->pmd_cleanup(cpu);
            }
            FREE(md, M_PMC);
            md = NULL;
            pmc_restore_cpu_binding(&pb);
      }

      /* deallocate per-cpu structures */
      FREE(pmc_pcpu, M_PMC);
      pmc_pcpu = NULL;

      FREE(pmc_pcpu_saved, M_PMC);
      pmc_pcpu_saved = NULL;

      if (pmc_pmcdisp) {
            FREE(pmc_pmcdisp, M_PMC);
            pmc_pmcdisp = NULL;
      }

      pmclog_shutdown();

      sx_xunlock(&pmc_sx);    /* we are done */
}

/*
 * The function called at load/unload.
 */

static int
load (struct module *module __unused, int cmd, void *arg __unused)
{
      int error;

      error = 0;

      switch (cmd) {
      case MOD_LOAD :
            /* initialize the subsystem */
            error = pmc_initialize();
            if (error != 0)
                  break;
            PMCDBG(MOD,INI,1, "syscall=%d ncpus=%d",
                pmc_syscall_num, mp_ncpus);
            break;


      case MOD_UNLOAD :
      case MOD_SHUTDOWN:
            pmc_cleanup();
            PMCDBG(MOD,INI,1, "%s", "unloaded");
            break;

      default :
            error = EINVAL;   /* XXX should panic(9) */
            break;
      }

      return error;
}

/* memory pool */
MALLOC_DEFINE(M_PMC, "pmc", "Memory space for the PMC module");

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