xen/dtrace/xdt.c

	xdt.c revision 193974072f41a843678abf5f61979c748687e66b
/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */

/*
 * Copyright 2008 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

/*
 * Xen event provider for DTrace
 *
 * NOTE: This provider is PRIVATE. It is intended as a short-term solution and
 * may disappear or be re-implemented at anytime.
 *
 * This provider isn't suitable as a general-purpose solution for a number of
 * reasons. First and foremost, we rely on the Xen tracing mechanism and don't
 * have any way to gather data other than that collected by the Xen trace
 * buffers. Further, it does not fit into the DTrace model (see "Interacting
 * with DTrace" below.)
 *
 *
 * Tracing in Xen
 * --------------
 *
 * Xen implements a tracing facility for generating and collecting execution
 * event traces from the hypervisor. When tracing is enabled, compiled in
 * probes record events in contiguous per-CPU trace buffers.
 *
 *               +---------+
 * +------+      |         |
 * | CPUn |----> | BUFFERn |
 * +------+      |         |
 *               +---------+- tbuf.va + (tbuf.size * n)
 *               :         :
 *               +---------+
 * +------+      |         |
 * | CPU1 |----> | BUFFER1 |
 * +------+      |         |
 *               +---------+- tbuf.va + tbuf.size
 * +------+      |         |
 * | CPU0 |----> | BUFFER0 |
 * +------+      |         |
 *               +---------+- tbuf.va
 *
 * Each CPU buffer consists of a metadata header followed by the trace records.
 * The metadata consists of a producer/consumer pair of pointers into the buffer
 * that point to the next record to be written and the next record to be read
 * respectively. The trace record format is as follows:
 *
 * +--------------------------------------------------------------------------+
 * | CPUID(uint_t) | TSC(uint64_t) | EVENTID(uint32_t) |     DATA FIELDS      |
 * +--------------------------------------------------------------------------+
 *
 * DATA FIELDS:
 * +--------------------------------------------------------------------------+
 * | D1(uint32_t) | D2(uint32_t) | D3(uint32_t) | D4(uint32_t) | D5(uint32_t) |
 * +--------------------------------------------------------------------------+
 *
 *
 * Interacting with DTrace
 * -----------------------
 *
 * Every xdt_poll_nsec nano-seconds we poll the trace buffers for data and feed
 * each entry into dtrace_probe() with the corresponding probe ID for the event.
 * As a result of this periodic collection implementation probe firings are
 * asynchronous. This is the only sensible way to implement this form of
 * provider, but because of its asynchronous nature asking things like
 * "current CPU" and, more importantly, arbitrary questions about the context
 * surrounding the probe firing are not meaningful. So, consumers should not
 * attempt to infer anything beyond what is supplied via the probe arguments.
 */

#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/modctl.h>
#include <sys/sunddi.h>
#include <sys/ddi.h>
#include <sys/conf.h>
#include <sys/devops.h>
#include <sys/stat.h>
#include <sys/cmn_err.h>
#include <sys/dtrace.h>
#include <sys/sdt.h>
#include <sys/cyclic.h>
#include <vm/seg_kmem.h>
#include <vm/hat_i86.h>
#include <sys/hypervisor.h>
#include <xen/public/trace.h>
#include <xen/public/sched.h>

#define XDT_POLL_DEFAULT    100000000   /* default poll interval (ns) */
#define XDT_POLL_MIN        10000000    /* min poll interval (ns) */
#define XDT_TBUF_RETRY      50      /* tbuf disable retry count */

/*
 * The domid must match IDLE_DOMAIN_ID in xen.hg/xen/include/xen/sched.h
 * in the xVM gate.
 */
#define IS_IDLE_DOM(domid)  (domid == 0x7FFFU)

/* Macros to extract the domid and cpuid from a HVM trace data field */
#define HVM_DOMID(d)        (d >> 16)
#define HVM_VCPUID(d)       (d & 0xFFFF)

#define XDT_PROBE4(event, cpuid, arg0, arg1, arg2, arg3) {      \
    dtrace_id_t id = xdt_probemap[event];               \
    if (id)                             \
        dtrace_probe(id, cpuid, arg0, arg1, arg2, arg3);    \
}                                   \

#define XDT_PROBE3(event, cpuid, arg0, arg1, arg2) \
    XDT_PROBE4(event, cpuid, arg0, arg1, arg2, 0)

#define XDT_PROBE2(event, cpuid, arg0, arg1) \
    XDT_PROBE4(event, cpuid, arg0, arg1, 0, 0)

#define XDT_PROBE1(event, cpuid, arg0) \
    XDT_PROBE4(event, cpuid, arg0, 0, 0, 0)

#define XDT_PROBE0(event, cpuid) \
    XDT_PROBE4(event, cpuid, 0, 0, 0, 0)

/* Probe classes */
#define XDT_SCHED           0
#define XDT_MEM             1
#define XDT_HVM             2
#define XDT_NCLASSES            3

/* Probe events */
#define XDT_EVT_INVALID         (-(int)1)
#define XDT_SCHED_OFF_CPU       0
#define XDT_SCHED_ON_CPU        1
#define XDT_SCHED_IDLE_OFF_CPU      2
#define XDT_SCHED_IDLE_ON_CPU       3
#define XDT_SCHED_BLOCK         4
#define XDT_SCHED_SLEEP         5
#define XDT_SCHED_WAKE          6
#define XDT_SCHED_YIELD         7
#define XDT_SCHED_SHUTDOWN_POWEROFF 8
#define XDT_SCHED_SHUTDOWN_REBOOT   9
#define XDT_SCHED_SHUTDOWN_SUSPEND  10
#define XDT_SCHED_SHUTDOWN_CRASH    11
#define XDT_MEM_PAGE_GRANT_MAP      12
#define XDT_MEM_PAGE_GRANT_UNMAP    13
#define XDT_MEM_PAGE_GRANT_TRANSFER 14
#define XDT_HVM_VMENTRY         15
#define XDT_HVM_VMEXIT          16
#define XDT_NEVENTS         17

typedef struct {
    const char  *pr_mod;    /* probe module */
    const char  *pr_name;   /* probe name */
    int     evt_id;     /* event id */
    uint_t      class;      /* probe class */
} xdt_probe_t;

typedef struct {
    uint32_t    trc_mask;   /* trace mask */
    uint32_t    cnt;        /* num enabled probes in class */
} xdt_classinfo_t;

typedef struct {
    ulong_t prev_domid;     /* previous dom executed */
    ulong_t prev_vcpuid;        /* previous vcpu executed */
    ulong_t prev_ctime;     /* time spent on cpu */
    ulong_t next_domid;     /* next dom to be scheduled */
    ulong_t next_vcpuid;        /* next vcpu to be scheduled */
    ulong_t next_wtime;     /* time spent waiting to get on cpu */
    ulong_t next_ts;        /* allocated time slice */
} xdt_schedinfo_t;

static struct {
    uint_t cnt;         /* total num of trace buffers */
    size_t size;            /* size of each cpu buffer */
    mfn_t start_mfn;        /* starting mfn of buffers */
    caddr_t va;         /* va buffers are mapped into */

    /* per-cpu buffers */
    struct t_buf **meta;        /* buffer metadata */
    struct t_rec **data;        /* buffer data records */

    /* statistics */
    uint64_t stat_dropped_recs; /* records dropped */
    uint64_t stat_spurious_cpu; /* recs with garbage cpuids */
    uint64_t stat_spurious_switch;  /* inconsistent vcpu switches */
    uint64_t stat_unknown_shutdown; /* unknown shutdown code */
    uint64_t stat_unknown_recs; /* unknown records */
} tbuf;

static char *xdt_stats[] = {
    "dropped_recs",
};

/*
 * Tunable variables
 *
 * The following may be tuned by adding a line to /etc/system that
 * includes both the name of the module ("xdt") and the name of the variable.
 * For example:
 *     set xdt:xdt_tbuf_pages = 40
 */
uint_t xdt_tbuf_pages = 20;         /* pages to alloc per-cpu buf */

/*
 * The following may be tuned by adding a line to
 * /platform/i86xpv/kernel/drv/xdt.conf.
 * For example:
 *     xdt_poll_nsec = 200000000;
 */
static hrtime_t xdt_poll_nsec;          /* trace buffer poll interval */

/*
 * Internal variables
 */
static dev_info_t *xdt_devi;
static dtrace_provider_id_t xdt_id;
static uint_t xdt_ncpus;            /* total number of phys CPUs */
static uint32_t cur_trace_mask;         /* current trace mask */
static xdt_schedinfo_t *xdt_cpu_schedinfo;  /* per-cpu sched info */
dtrace_id_t xdt_probemap[XDT_NEVENTS];      /* map of enabled probes */
dtrace_id_t xdt_prid[XDT_NEVENTS];      /* IDs of registered events */
static cyclic_id_t xdt_cyclic = CYCLIC_NONE;
static kstat_t *xdt_kstats;
static xdt_classinfo_t xdt_classinfo[XDT_NCLASSES];

static xdt_probe_t xdt_probe[] = {
    /* Sched probes */
    { "sched", "off-cpu", XDT_SCHED_OFF_CPU, XDT_SCHED },
    { "sched", "on-cpu", XDT_SCHED_ON_CPU, XDT_SCHED },
    { "sched", "idle-off-cpu", XDT_SCHED_IDLE_OFF_CPU, XDT_SCHED },
    { "sched", "idle-on-cpu", XDT_SCHED_IDLE_ON_CPU, XDT_SCHED },
    { "sched", "block", XDT_SCHED_BLOCK, XDT_SCHED },
    { "sched", "sleep", XDT_SCHED_SLEEP, XDT_SCHED },
    { "sched", "wake", XDT_SCHED_WAKE, XDT_SCHED },
    { "sched", "yield", XDT_SCHED_YIELD, XDT_SCHED },
    { "sched", "shutdown-poweroff", XDT_SCHED_SHUTDOWN_POWEROFF,
        XDT_SCHED },
    { "sched", "shutdown-reboot", XDT_SCHED_SHUTDOWN_REBOOT, XDT_SCHED },
    { "sched", "shutdown-suspend", XDT_SCHED_SHUTDOWN_SUSPEND, XDT_SCHED },
    { "sched", "shutdown-crash", XDT_SCHED_SHUTDOWN_CRASH, XDT_SCHED },

    /* Memory probes */
    { "mem", "page-grant-map", XDT_MEM_PAGE_GRANT_MAP, XDT_MEM },
    { "mem", "page-grant-unmap", XDT_MEM_PAGE_GRANT_UNMAP, XDT_MEM },
    { "mem", "page-grant-transfer", XDT_MEM_PAGE_GRANT_TRANSFER, XDT_MEM },

    /* HVM probes */
    { "hvm", "vmentry", XDT_HVM_VMENTRY, XDT_HVM },
    { "hvm", "vmexit", XDT_HVM_VMEXIT, XDT_HVM },

    { NULL }
};

extern uint_t xen_get_nphyscpus(void);

static inline uint32_t
xdt_nr_active_probes()
{
    int i;
    uint32_t tot = 0;

    for (i = 0; i < XDT_NCLASSES; i++)
        tot += xdt_classinfo[i].cnt;

    return (tot);
}

static void
xdt_init_trace_masks(void)
{
    xdt_classinfo[XDT_SCHED].trc_mask = TRC_SCHED;
    xdt_classinfo[XDT_MEM].trc_mask = TRC_MEM;
    xdt_classinfo[XDT_HVM].trc_mask = TRC_HVM;
}

static int
xdt_kstat_update(kstat_t *ksp, int flag)
{
    kstat_named_t *knp;

    if (flag != KSTAT_READ)
        return (EACCES);

    knp = ksp->ks_data;

    /*
     * Assignment order should match that of the names in
     * xdt_stats.
     */
    (knp++)->value.ui64 = tbuf.stat_dropped_recs;

    return (0);
}

static void
xdt_kstat_init(void)
{
    int nstats = sizeof (xdt_stats) / sizeof (xdt_stats[0]);
    char **cp = xdt_stats;
    kstat_named_t *knp;

    if ((xdt_kstats = kstat_create("xdt", 0, "trace_statistics", "misc",
        KSTAT_TYPE_NAMED, nstats, 0)) == NULL)
        return;

    xdt_kstats->ks_update = xdt_kstat_update;

    knp = xdt_kstats->ks_data;
    while (nstats > 0) {
        kstat_named_init(knp, *cp, KSTAT_DATA_UINT64);
        knp++;
        cp++;
        nstats--;
    }

    kstat_install(xdt_kstats);
}

static int
xdt_sysctl_tbuf(xen_sysctl_tbuf_op_t *tbuf_op)
{
    xen_sysctl_t op;
    int xerr;

    op.cmd = XEN_SYSCTL_tbuf_op;
    op.interface_version = XEN_SYSCTL_INTERFACE_VERSION;
    op.u.tbuf_op = *tbuf_op;

    if ((xerr = HYPERVISOR_sysctl(&op)) != 0)
        return (xen_xlate_errcode(xerr));

    *tbuf_op = op.u.tbuf_op;
    return (0);
}

static int
xdt_map_trace_buffers(mfn_t mfn, caddr_t va, size_t len)
{
    x86pte_t pte;
    caddr_t const sva = va;
    caddr_t const eva = va + len;
    int xerr;

    ASSERT(mfn != MFN_INVALID);
    ASSERT(va != NULL);
    ASSERT(IS_PAGEALIGNED(len));

    for (; va < eva; va += MMU_PAGESIZE) {
        /*
         * Ask the HAT to load a throwaway mapping to page zero, then
         * overwrite it with the hypervisor mapping. It gets removed
         * later via hat_unload().
         */
        hat_devload(kas.a_hat, va, MMU_PAGESIZE, (pfn_t)0,
            PROT_READ | HAT_UNORDERED_OK,
            HAT_LOAD_NOCONSIST | HAT_LOAD);

        pte = mmu_ptob((x86pte_t)mfn) | PT_VALID | PT_USER
            | PT_FOREIGN | PT_WRITABLE;

        xerr = HYPERVISOR_update_va_mapping_otherdomain((ulong_t)va,
            pte, UVMF_INVLPG | UVMF_LOCAL, DOMID_XEN);

        if (xerr != 0) {
            /* unmap pages loaded so far */
            size_t ulen = (uintptr_t)(va + MMU_PAGESIZE) -
                (uintptr_t)sva;
            hat_unload(kas.a_hat, sva, ulen, HAT_UNLOAD_UNMAP);
            return (xen_xlate_errcode(xerr));
        }

        mfn++;
    }

    return (0);
}

static int
xdt_attach_trace_buffers(void)
{
    xen_sysctl_tbuf_op_t tbuf_op;
    size_t len;
    int err;
    uint_t i;

    /*
     * Xen does not support trace buffer re-sizing. If the buffers
     * have already been allocated we just use them as is.
     */
    tbuf_op.cmd  = XEN_SYSCTL_TBUFOP_get_info;
    if ((err = xdt_sysctl_tbuf(&tbuf_op)) != 0)
        return (err);

    if (tbuf_op.size == 0) {
        /* set trace buffer size */
        tbuf_op.cmd  = XEN_SYSCTL_TBUFOP_set_size;
        tbuf_op.size = xdt_tbuf_pages;
        (void) xdt_sysctl_tbuf(&tbuf_op);

        /* get trace buffer info */
        tbuf_op.cmd  = XEN_SYSCTL_TBUFOP_get_info;
        if ((err = xdt_sysctl_tbuf(&tbuf_op)) != 0)
            return (err);

        if (tbuf_op.size == 0) {
            cmn_err(CE_NOTE, "Couldn't allocate trace buffers.");
            return (ENOBUFS);
        }
    }

    tbuf.size = tbuf_op.size;
    tbuf.start_mfn = (mfn_t)tbuf_op.buffer_mfn;
    tbuf.cnt = xdt_ncpus;

    ASSERT(tbuf.start_mfn != MFN_INVALID);
    ASSERT(tbuf.cnt > 0);

    len = tbuf.size * tbuf.cnt;
    tbuf.va = vmem_alloc(heap_arena, len, VM_SLEEP);

    if ((err = xdt_map_trace_buffers(tbuf.start_mfn, tbuf.va, len)) != 0) {
        vmem_free(heap_arena, tbuf.va, len);
        tbuf.va = NULL;
        return (err);
    }

    tbuf.meta = (struct t_buf **)kmem_alloc(tbuf.cnt * sizeof (*tbuf.meta),
        KM_SLEEP);
    tbuf.data = (struct t_rec **)kmem_alloc(tbuf.cnt * sizeof (*tbuf.data),
        KM_SLEEP);

    for (i = 0; i < tbuf.cnt; i++) {
        void *cpu_buf = (void *)(tbuf.va + (tbuf.size * i));
        tbuf.meta[i] = cpu_buf;
        tbuf.data[i] = (struct t_rec *)((uintptr_t)cpu_buf +
            sizeof (struct t_buf));

        /* throw away stale trace records */
        tbuf.meta[i]->cons = tbuf.meta[i]->prod;
    }

    return (0);
}

static void
xdt_detach_trace_buffers(void)
{
    size_t len = tbuf.size * tbuf.cnt;

    ASSERT(tbuf.va != NULL);

    hat_unload(kas.a_hat, tbuf.va, len,
        HAT_UNLOAD_UNMAP | HAT_UNLOAD_UNLOCK);
    vmem_free(heap_arena, tbuf.va, len);
    kmem_free(tbuf.meta, tbuf.cnt * sizeof (*tbuf.meta));
    kmem_free(tbuf.data, tbuf.cnt * sizeof (*tbuf.data));
}

static inline void
xdt_process_rec(uint_t cpuid, struct t_rec *rec)
{
    xdt_schedinfo_t *sp = &xdt_cpu_schedinfo[cpuid];
    int eid;

    ASSERT(rec != NULL);
    ASSERT(xdt_ncpus == xen_get_nphyscpus());

    if (cpuid >= xdt_ncpus) {
        tbuf.stat_spurious_cpu++;
        return;
    }

    switch (rec->event) {

    /*
     * Sched probes
     */
    case TRC_SCHED_SWITCH_INFPREV:
        /*
         * Info on vCPU being de-scheduled
         *
         * rec->data[0] = prev domid
         * rec->data[1] = time spent on pcpu
         */
        sp->prev_domid = rec->data[0];
        sp->prev_ctime = rec->data[1];
        break;

    case TRC_SCHED_SWITCH_INFNEXT:
        /*
         * Info on next vCPU to be scheduled
         *
         * rec->data[0] = next domid
         * rec->data[1] = time spent waiting to get on cpu
         * rec->data[2] = time slice
         */
        sp->next_domid = rec->data[0];
        sp->next_wtime = rec->data[1];
        sp->next_ts = rec->data[2];
        break;

    case TRC_SCHED_SWITCH:
        /*
         * vCPU switch
         *
         * rec->data[0] = prev domid
         * rec->data[1] = prev vcpuid
         * rec->data[2] = next domid
         * rec->data[3] = next vcpuid
         */
        if (rec->data[0] != sp->prev_domid &&
            rec->data[2] != sp->next_domid) {
            /* prev and next info don't match doms being sched'd */
            tbuf.stat_spurious_switch++;
            return;
        }

        sp->prev_vcpuid = rec->data[1];
        sp->next_vcpuid = rec->data[3];

        XDT_PROBE3(IS_IDLE_DOM(sp->prev_domid)?
            XDT_SCHED_IDLE_OFF_CPU:XDT_SCHED_OFF_CPU,
            cpuid, sp->prev_domid, sp->prev_vcpuid, sp->prev_ctime);

        XDT_PROBE4(IS_IDLE_DOM(sp->next_domid)?
            XDT_SCHED_IDLE_ON_CPU:XDT_SCHED_ON_CPU,
            cpuid, sp->next_domid, sp->next_vcpuid, sp->next_wtime,
            sp->next_ts);
        break;

    case TRC_SCHED_BLOCK:
        /*
         * vCPU blocked
         *
         * rec->data[0] = domid
         * rec->data[1] = vcpuid
         */
        XDT_PROBE2(XDT_SCHED_BLOCK, cpuid, rec->data[0], rec->data[1]);
        break;

    case TRC_SCHED_SLEEP:
        /*
         * Put vCPU to sleep
         *
         * rec->data[0] = domid
         * rec->data[1] = vcpuid
         */
        XDT_PROBE2(XDT_SCHED_SLEEP, cpuid, rec->data[0], rec->data[1]);
        break;

    case TRC_SCHED_WAKE:
        /*
         * Wake up vCPU
         *
         * rec->data[0] = domid
         * rec->data[1] = vcpuid
         */
        XDT_PROBE2(XDT_SCHED_WAKE, cpuid, rec->data[0], rec->data[1]);
        break;

    case TRC_SCHED_YIELD:
        /*
         * vCPU yielded
         *
         * rec->data[0] = domid
         * rec->data[1] = vcpuid
         */
        XDT_PROBE2(XDT_SCHED_YIELD, cpuid, rec->data[0], rec->data[1]);
        break;

    case TRC_SCHED_SHUTDOWN:
        /*
         * Guest shutting down
         *
         * rec->data[0] = domid
         * rec->data[1] = initiating vcpu
         * rec->data[2] = shutdown code
         */
        switch (rec->data[2]) {
        case SHUTDOWN_poweroff:
            eid = XDT_SCHED_SHUTDOWN_POWEROFF;
            break;
        case SHUTDOWN_reboot:
            eid = XDT_SCHED_SHUTDOWN_REBOOT;
            break;
        case SHUTDOWN_suspend:
            eid = XDT_SCHED_SHUTDOWN_SUSPEND;
            break;
        case SHUTDOWN_crash:
            eid = XDT_SCHED_SHUTDOWN_CRASH;
            break;
        default:
            tbuf.stat_unknown_shutdown++;
            return;
        }

        XDT_PROBE1(eid, cpuid, rec->data[0]);
        break;

    /*
     * Mem probes
     */
    case TRC_MEM_PAGE_GRANT_MAP:
        /*
         * Guest mapped page grant
         *
         * rec->data[0] = domid
         */
        XDT_PROBE1(XDT_MEM_PAGE_GRANT_MAP, cpuid, rec->data[0]);
        break;

    case TRC_MEM_PAGE_GRANT_UNMAP:
        /*
         * Guest unmapped page grant
         *
         * rec->data[0] = domid
         */
        XDT_PROBE1(XDT_MEM_PAGE_GRANT_UNMAP, cpuid, rec->data[0]);
        break;

    case TRC_MEM_PAGE_GRANT_TRANSFER:
        /*
         * Page grant is being transferred
         *
         * rec->data[0] = target domid
         */
        XDT_PROBE1(XDT_MEM_PAGE_GRANT_TRANSFER, cpuid, rec->data[0]);
        break;

    /*
     * HVM probes
     */
    case TRC_HVM_VMENTRY:
        /*
         * Return to guest via vmx_launch/vmrun
         *
         * rec->data[0] = (domid<<16 + vcpuid)
         */
        XDT_PROBE2(XDT_HVM_VMENTRY, cpuid, HVM_DOMID(rec->data[0]),
            HVM_VCPUID(rec->data[0]));
        break;

    case TRC_HVM_VMEXIT:
        /*
         * Entry into VMEXIT handler
         *
         * rec->data[0] = (domid<<16 + vcpuid)
         * rec->data[1] = guest rip
         * rec->data[2] = cpu vendor specific exit code
         */
        XDT_PROBE4(XDT_HVM_VMEXIT, cpuid, HVM_DOMID(rec->data[0]),
            HVM_VCPUID(rec->data[0]), rec->data[1], rec->data[2]);
        break;

    case TRC_LOST_RECORDS:
        tbuf.stat_dropped_recs++;
        break;

    default:
        tbuf.stat_unknown_recs++;
        break;
    }
}

/*ARGSUSED*/
static void
xdt_tbuf_scan(void *arg)
{
    uint_t cpuid;
    size_t nrecs;
    struct t_rec *rec;
    uint32_t prod;

    nrecs = (tbuf.size - sizeof (struct t_buf)) / sizeof (struct t_rec);

    /* scan all cpu buffers for new records */
    for (cpuid = 0; cpuid < tbuf.cnt; cpuid++) {
        prod = tbuf.meta[cpuid]->prod;
        membar_consumer(); /* read prod /then/ data */
        while (tbuf.meta[cpuid]->cons != prod) {
            rec = tbuf.data[cpuid] + tbuf.meta[cpuid]->cons % nrecs;
            xdt_process_rec(cpuid, rec);
            membar_exit(); /* read data /then/ update cons */
            tbuf.meta[cpuid]->cons++;
        }
    }
}

static void
xdt_cyclic_enable(void)
{
    cyc_handler_t hdlr;
    cyc_time_t when;

    ASSERT(MUTEX_HELD(&cpu_lock));

    hdlr.cyh_func = xdt_tbuf_scan;
    hdlr.cyh_arg = NULL;
    hdlr.cyh_level = CY_LOW_LEVEL;

    when.cyt_interval = xdt_poll_nsec;
    when.cyt_when = dtrace_gethrtime() + when.cyt_interval;

    xdt_cyclic = cyclic_add(&hdlr, &when);
}

static void
xdt_probe_create(xdt_probe_t *p)
{
    ASSERT(p != NULL && p->pr_mod != NULL);

    if (dtrace_probe_lookup(xdt_id, p->pr_mod, NULL, p->pr_name) != 0)
        return;

    xdt_prid[p->evt_id] = dtrace_probe_create(xdt_id, p->pr_mod, NULL,
        p->pr_name, dtrace_mach_aframes(), p);
}

/*ARGSUSED*/
static void
xdt_provide(void *arg, const dtrace_probedesc_t *desc)
{
    const char *mod, *name;
    int i;

    if (desc == NULL) {
        for (i = 0; xdt_probe[i].pr_mod != NULL; i++) {
            xdt_probe_create(&xdt_probe[i]);
        }
    } else {
        mod = desc->dtpd_mod;
        name = desc->dtpd_name;
        for (i = 0; xdt_probe[i].pr_mod != NULL; i++) {
            int l1 = strlen(xdt_probe[i].pr_name);
            int l2 = strlen(xdt_probe[i].pr_mod);
            if (strncmp(name, xdt_probe[i].pr_name, l1) == 0 &&
                strncmp(mod, xdt_probe[i].pr_mod, l2) == 0)
                break;
        }

        if (xdt_probe[i].pr_mod == NULL)
            return;
        xdt_probe_create(&xdt_probe[i]);
    }

}

/*ARGSUSED*/
static void
xdt_destroy(void *arg, dtrace_id_t id, void *parg)
{
    xdt_probe_t *p = parg;
    xdt_prid[p->evt_id] = 0;
}

static void
xdt_set_trace_mask(uint32_t mask)
{
    xen_sysctl_tbuf_op_t tbuf_op;

    tbuf_op.cmd  = XEN_SYSCTL_TBUFOP_set_evt_mask;
    tbuf_op.evt_mask = mask;
    (void) xdt_sysctl_tbuf(&tbuf_op);
}

/*ARGSUSED*/
static void
xdt_enable(void *arg, dtrace_id_t id, void *parg)
{
    xdt_probe_t *p = parg;
    xen_sysctl_tbuf_op_t tbuf_op;

    ASSERT(MUTEX_HELD(&cpu_lock));
    ASSERT(xdt_prid[p->evt_id] != 0);

    xdt_probemap[p->evt_id] = xdt_prid[p->evt_id];
    xdt_classinfo[p->class].cnt++;

    if (xdt_classinfo[p->class].cnt == 1) {
        /* set the trace mask for this class */
        cur_trace_mask |= xdt_classinfo[p->class].trc_mask;
        xdt_set_trace_mask(cur_trace_mask);
    }

    if (xdt_cyclic == CYCLIC_NONE) {
        /*
         * DTrace doesn't have the notion of failing an enabling. It
         * works on the premise that, if you have advertised a probe
         * via the pops->dtps_provide() function, you can enable it.
         * Failure is not an option. In the case where we can't enable
         * Xen tracing the consumer will carry on regardless and
         * think all is OK except the probes will never fire.
         */
        tbuf_op.cmd = XEN_SYSCTL_TBUFOP_enable;
        if (xdt_sysctl_tbuf(&tbuf_op) != 0) {
            cmn_err(CE_NOTE, "Couldn't enable hypervisor tracing.");
            return;
        }

        xdt_cyclic_enable();
    }
}

/*ARGSUSED*/
static void
xdt_disable(void *arg, dtrace_id_t id, void *parg)
{
    xdt_probe_t *p = parg;
    xen_sysctl_tbuf_op_t tbuf_op;
    int i, err;

    ASSERT(MUTEX_HELD(&cpu_lock));
    ASSERT(xdt_probemap[p->evt_id] != 0);
    ASSERT(xdt_probemap[p->evt_id] == xdt_prid[p->evt_id]);
    ASSERT(xdt_classinfo[p->class].cnt > 0);

    /*
     * We could be here in the slight window between the cyclic firing and
     * a call to dtrace_probe() occurring. We need to be careful if we tear
     * down any shared state.
     */

    xdt_probemap[p->evt_id] = 0;
    xdt_classinfo[p->class].cnt--;

    if (xdt_nr_active_probes() == 0) {
        cur_trace_mask = 0;

        if (xdt_cyclic == CYCLIC_NONE)
            return;

        /*
         * We will try to disable the trace buffers. If we fail for some
         * reason we will try again, up to a count of XDT_TBUF_RETRY.
         * If we still aren't successful we try to set the trace mask
         * to 0 in order to prevent trace records from being written.
         */
        tbuf_op.cmd = XEN_SYSCTL_TBUFOP_disable;
        i = 0;
        do {
            err = xdt_sysctl_tbuf(&tbuf_op);
        } while ((err != 0) && (++i < XDT_TBUF_RETRY));

        if (err != 0) {
            cmn_err(CE_NOTE,
                "Couldn't disable hypervisor tracing.");
            xdt_set_trace_mask(0);
        } else {
            cyclic_remove(xdt_cyclic);
            xdt_cyclic = CYCLIC_NONE;
            /*
             * We don't bother making the hypercall to set
             * the trace mask, since it will be reset when
             * tracing is re-enabled.
             */
        }
    } else if (xdt_classinfo[p->class].cnt == 0) {
        cur_trace_mask ^= xdt_classinfo[p->class].trc_mask;
        /* other probes are enabled, so add the sub-class mask back */
        cur_trace_mask |= 0xF000;
        xdt_set_trace_mask(cur_trace_mask);
    }
}

static dtrace_pattr_t xdt_attr = {
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_PLATFORM },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_PLATFORM },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_UNKNOWN },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_PLATFORM },
{ DTRACE_STABILITY_PRIVATE, DTRACE_STABILITY_PRIVATE, DTRACE_CLASS_PLATFORM },
};

static dtrace_pops_t xdt_pops = {
    xdt_provide,        /* dtps_provide() */
    NULL,           /* dtps_provide_module() */
    xdt_enable,     /* dtps_enable() */
    xdt_disable,        /* dtps_disable() */
    NULL,           /* dtps_suspend() */
    NULL,           /* dtps_resume() */
    NULL,           /* dtps_getargdesc() */
    NULL,           /* dtps_getargval() */
    NULL,           /* dtps_usermode() */
    xdt_destroy     /* dtps_destroy() */
};

static int
xdt_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
{
    int val;

    if (!DOMAIN_IS_INITDOMAIN(xen_info))
        return (DDI_FAILURE);

    switch (cmd) {
    case DDI_ATTACH:
        break;

    case DDI_RESUME:
        /*
         * We might support proper suspend/resume in the future, so,
         * return DDI_FAILURE for now.
         */
        return (DDI_FAILURE);

    default:
        return (DDI_FAILURE);
    }

    xdt_ncpus = xen_get_nphyscpus();
    ASSERT(xdt_ncpus > 0);

    if (ddi_create_minor_node(devi, "xdt", S_IFCHR, 0, DDI_PSEUDO, 0) ==
        DDI_FAILURE || xdt_attach_trace_buffers() != 0 ||
        dtrace_register("xdt", &xdt_attr, DTRACE_PRIV_KERNEL, NULL,
        &xdt_pops, NULL, &xdt_id) != 0) {
        if (tbuf.va != NULL)
            xdt_detach_trace_buffers();
        ddi_remove_minor_node(devi, NULL);
        return (DDI_FAILURE);
    }

    val = ddi_getprop(DDI_DEV_T_ANY, devi, DDI_PROP_DONTPASS,
        "xdt_poll_nsec", XDT_POLL_DEFAULT);
    xdt_poll_nsec = MAX(val, XDT_POLL_MIN);

    xdt_cpu_schedinfo = (xdt_schedinfo_t *)kmem_alloc(xdt_ncpus *
        sizeof (xdt_schedinfo_t), KM_SLEEP);
    xdt_init_trace_masks();
    xdt_kstat_init();

    xdt_devi = devi;
    ddi_report_dev(devi);
    return (DDI_SUCCESS);
}

static int
xdt_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
{
    switch (cmd) {
    case DDI_DETACH:
        break;

    case DDI_SUSPEND:
        /*
         * We might support proper suspend/resume in the future. So
         * return DDI_FAILURE for now.
         */
        return (DDI_FAILURE);

    default:
        return (DDI_FAILURE);
    }

    if (dtrace_unregister(xdt_id) != 0)
        return (DDI_FAILURE);

    xdt_detach_trace_buffers();
    kmem_free(xdt_cpu_schedinfo, xdt_ncpus * sizeof (xdt_schedinfo_t));
    if (xdt_cyclic != CYCLIC_NONE)
        cyclic_remove(xdt_cyclic);
    if (xdt_kstats != NULL)
        kstat_delete(xdt_kstats);
    xdt_devi = (void *)0;
    ddi_remove_minor_node(devi, NULL);

    return (DDI_SUCCESS);
}

/*ARGSUSED*/
static int
xdt_info(dev_info_t *devi, ddi_info_cmd_t infocmd, void *arg, void **result)
{
    int error;

    switch (infocmd) {
    case DDI_INFO_DEVT2DEVINFO:
        *result = xdt_devi;
        error = DDI_SUCCESS;
        break;
    case DDI_INFO_DEVT2INSTANCE:
        *result = (void *)0;
        error = DDI_SUCCESS;
        break;
    default:
        error = DDI_FAILURE;
    }
    return (error);
}

static struct cb_ops xdt_cb_ops = {
    nulldev,        /* open(9E) */
    nodev,          /* close(9E) */
    nodev,          /* strategy(9E) */
    nodev,          /* print(9E) */
    nodev,          /* dump(9E) */
    nodev,          /* read(9E) */
    nodev,          /* write(9E) */
    nodev,          /* ioctl(9E) */
    nodev,          /* devmap(9E) */
    nodev,          /* mmap(9E) */
    nodev,          /* segmap(9E) */
    nochpoll,       /* chpoll(9E) */
    ddi_prop_op,        /* prop_op(9E) */
    NULL,           /* streamtab(9S) */
    D_MP | D_64BIT | D_NEW  /* cb_flag */
};

static struct dev_ops xdt_ops = {
    DEVO_REV,       /* devo_rev */
    0,          /* devo_refcnt */
    xdt_info,       /* getinfo(9E) */
    nulldev,        /* identify(9E) */
    nulldev,        /* probe(9E) */
    xdt_attach,     /* attach(9E) */
    xdt_detach,     /* detach(9E) */
    nulldev,        /* devo_reset */
    &xdt_cb_ops,        /* devo_cb_ops */
    NULL,           /* devo_bus_ops */
    NULL,           /* power(9E) */
    ddi_quiesce_not_needed,     /* devo_quiesce */
};


static struct modldrv modldrv = {
    &mod_driverops,
    "Hypervisor event tracing",
    &xdt_ops
};

static struct modlinkage modlinkage = {
    MODREV_1,
    &modldrv,
    NULL
};

int
_init(void)
{
    return (mod_install(&modlinkage));
}

int
_fini(void)
{
    return (mod_remove(&modlinkage));
}

int
_info(struct modinfo *modinfop)
{
    return (mod_info(&modlinkage, modinfop));
}