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[unleashed.git] / kernel / vm / page_retire.c

/*
 * 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 2010 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 * Copyright (c) 2016 by Delphix. All rights reserved.
 */

/*
 * Page Retire - Big Theory Statement.
 *
 * This file handles removing sections of faulty memory from use when the
 * user land FMA Diagnosis Engine requests that a page be removed or when
 * a CE or UE is detected by the hardware.
 *
 * In the bad old days, the kernel side of Page Retire did a lot of the work
 * on its own. Now, with the DE keeping track of errors, the kernel side is
 * rather simple minded on most platforms.
 *
 * Errors are all reflected to the DE, and after digesting the error and
 * looking at all previously reported errors, the DE decides what should
 * be done about the current error. If the DE wants a particular page to
 * be retired, then the kernel page retire code is invoked via an ioctl.
 * On non-FMA platforms, the ue_drain and ce_drain paths ends up calling
 * page retire to handle the error. Since page retire is just a simple
 * mechanism it doesn't need to differentiate between the different callers.
 *
 * The p_toxic field in the page_t is used to indicate which errors have
 * occurred and what action has been taken on a given page. Because errors are
 * reported without regard to the locked state of a page, no locks are used
 * to SET the error bits in p_toxic. However, in order to clear the error
 * bits, the page_t must be held exclusively locked.
 *
 * When page_retire() is called, it must be able to acquire locks, sleep, etc.
 * It must not be called from high-level interrupt context.
 *
 * Depending on how the requested page is being used at the time of the retire
 * request (and on the availability of sufficient system resources), the page
 * may be retired immediately, or just marked for retirement later. For
 * example, locked pages are marked, while free pages are retired. Multiple
 * requests may be made to retire the same page, although there is no need
 * to: once the p_toxic flags are set, the page will be retired as soon as it
 * can be exclusively locked.
 *
 * The retire mechanism is driven centrally out of page_unlock(). To expedite
 * the retirement of pages, further requests for SE_SHARED locks are denied
 * as long as a page retirement is pending. In addition, as long as pages are
 * pending retirement a background thread runs periodically trying to retire
 * those pages. Pages which could not be retired while the system is running
 * are scrubbed prior to rebooting to avoid latent errors on the next boot.
 *
 * UE pages without persistent errors are scrubbed and returned to service.
 * Recidivist pages, as well as FMA-directed requests for retirement, result
 * in the page being taken out of service. Once the decision is made to take
 * a page out of service, the page is cleared, hashed onto the retired_pages
 * vnode, marked as retired, and it is unlocked.  No other requesters (except
 * for unretire) are allowed to lock retired pages.
 *
 * The public routines return (sadly) 0 if they worked and a non-zero error
 * value if something went wrong. This is done for the ioctl side of the
 * world to allow errors to be reflected all the way out to user land. The
 * non-zero values are explained in comments atop each function.
 */

/*
 * Things to fix:
 *
 *      1. Trying to retire non-relocatable kvp pages may result in a
 *      quagmire. This is because seg_kmem() no longer keeps its pages locked,
 *      and calls page_lookup() in the free path; since kvp pages are modified
 *      and don't have a usable backing store, page_retire() can't do anything
 *      with them, and we'll keep denying the lock to seg_kmem_free() in a
 *      vicious cycle. To prevent that, we don't deny locks to kvp pages, and
 *      hence only try to retire a page from page_unlock() in the free path.
 *      Since most kernel pages are indefinitely held anyway, and don't
 *      participate in I/O, this is of little consequence.
 *
 *      2. Low memory situations will be interesting. If we don't have
 *      enough memory for page_relocate() to succeed, we won't be able to
 *      retire dirty pages; nobody will be able to push them out to disk
 *      either, since we aggressively deny the page lock. We could change
 *      fsflush so it can recognize this situation, grab the lock, and push
 *      the page out, where we'll catch it in the free path and retire it.
 *
 *      3. Beware of places that have code like this in them:
 *
 *              if (! page_tryupgrade(pp)) {
 *                      page_unlock(pp);
 *                      while (! page_lock(pp, SE_EXCL, NULL, P_RECLAIM)) {
 *                              / *NOTHING* /
 *                      }
 *              }
 *              page_free(pp);
 *
 *      The problem is that pp can change identity right after the
 *      page_unlock() call.  In particular, page_retire() can step in
 *      there, change pp's identity, and hash pp onto the retired_vnode.
 *
 *      Of course, other functions besides page_retire() can have the
 *      same effect. A kmem reader can waltz by, set up a mapping to the
 *      page, and then unlock the page. Page_free() will then go castors
 *      up. So if anybody is doing this, it's already a bug.
 *
 *      4. mdboot()'s call into page_retire_mdboot() should probably be
 *      moved lower. Where the call is made now, we can get into trouble
 *      by scrubbing a kernel page that is then accessed later.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/mman.h>
#include <sys/vnode.h>
#include <sys/vfs.h>
#include <sys/cmn_err.h>
#include <sys/ksynch.h>
#include <sys/thread.h>
#include <sys/disp.h>
#include <sys/ontrap.h>
#include <sys/vmsystm.h>
#include <sys/mem_config.h>
#include <sys/atomic.h>
#include <sys/callb.h>
#include <sys/kobj.h>
#include <vm/page.h>
#include <vm/vm_dep.h>
#include <vm/as.h>
#include <vm/hat.h>
#include <vm/seg_kmem.h>

/*
 * vnode for all pages which are retired from the VM system;
 */
vnode_t *retired_pages;

/*
 * vnode ops - all defaults
 */
static const struct vnodeops retired_vnodeops = {
        .vnop_name = "retired_pages",
};

static int page_retire_pp_finish(page_t *, void *, uint_t);

/*
 * Make a list of all of the pages that have been marked for retirement
 * but are not yet retired.  At system shutdown, we will scrub all of the
 * pages in the list in case there are outstanding UEs.  Then, we
 * cross-check this list against the number of pages that are yet to be
 * retired, and if we find inconsistencies, we scan every page_t in the
 * whole system looking for any pages that need to be scrubbed for UEs.
 * The background thread also uses this queue to determine which pages
 * it should keep trying to retire.
 */
#ifdef  DEBUG
#define PR_PENDING_QMAX 32
#else   /* DEBUG */
#define PR_PENDING_QMAX 256
#endif  /* DEBUG */
page_t          *pr_pending_q[PR_PENDING_QMAX];
kmutex_t        pr_q_mutex;

/*
 * Page retire global kstats
 */
struct page_retire_kstat {
        kstat_named_t   pr_retired;
        kstat_named_t   pr_requested;
        kstat_named_t   pr_requested_free;
        kstat_named_t   pr_enqueue_fail;
        kstat_named_t   pr_dequeue_fail;
        kstat_named_t   pr_pending;
        kstat_named_t   pr_pending_kas;
        kstat_named_t   pr_failed;
        kstat_named_t   pr_failed_kernel;
        kstat_named_t   pr_limit;
        kstat_named_t   pr_limit_exceeded;
        kstat_named_t   pr_fma;
        kstat_named_t   pr_mce;
        kstat_named_t   pr_ue;
        kstat_named_t   pr_ue_cleared_retire;
        kstat_named_t   pr_ue_cleared_free;
        kstat_named_t   pr_ue_persistent;
        kstat_named_t   pr_unretired;
};

static struct page_retire_kstat page_retire_kstat = {
        { "pages_retired",              KSTAT_DATA_UINT64},
        { "pages_retire_request",       KSTAT_DATA_UINT64},
        { "pages_retire_request_free",  KSTAT_DATA_UINT64},
        { "pages_notenqueued",          KSTAT_DATA_UINT64},
        { "pages_notdequeued",          KSTAT_DATA_UINT64},
        { "pages_pending",              KSTAT_DATA_UINT64},
        { "pages_pending_kas",          KSTAT_DATA_UINT64},
        { "pages_deferred",             KSTAT_DATA_UINT64},
        { "pages_deferred_kernel",      KSTAT_DATA_UINT64},
        { "pages_limit",                KSTAT_DATA_UINT64},
        { "pages_limit_exceeded",       KSTAT_DATA_UINT64},
        { "pages_fma",                  KSTAT_DATA_UINT64},
        { "pages_multiple_ce",          KSTAT_DATA_UINT64},
        { "pages_ue",                   KSTAT_DATA_UINT64},
        { "pages_ue_cleared_retired",   KSTAT_DATA_UINT64},
        { "pages_ue_cleared_freed",     KSTAT_DATA_UINT64},
        { "pages_ue_persistent",        KSTAT_DATA_UINT64},
        { "pages_unretired",            KSTAT_DATA_UINT64},
};

static kstat_t  *page_retire_ksp = NULL;

#define PR_INCR_KSTAT(stat)     \
        atomic_inc_64(&(page_retire_kstat.stat.value.ui64))
#define PR_DECR_KSTAT(stat)     \
        atomic_dec_64(&(page_retire_kstat.stat.value.ui64))

#define PR_KSTAT_RETIRED_CE     (page_retire_kstat.pr_mce.value.ui64)
#define PR_KSTAT_RETIRED_FMA    (page_retire_kstat.pr_fma.value.ui64)
#define PR_KSTAT_RETIRED_NOTUE  (PR_KSTAT_RETIRED_CE + PR_KSTAT_RETIRED_FMA)
#define PR_KSTAT_PENDING        (page_retire_kstat.pr_pending.value.ui64)
#define PR_KSTAT_PENDING_KAS    (page_retire_kstat.pr_pending_kas.value.ui64)
#define PR_KSTAT_EQFAIL         (page_retire_kstat.pr_enqueue_fail.value.ui64)
#define PR_KSTAT_DQFAIL         (page_retire_kstat.pr_dequeue_fail.value.ui64)

/*
 * page retire kstats to list all retired pages
 */
static int pr_list_kstat_update(kstat_t *ksp, int rw);
static int pr_list_kstat_snapshot(kstat_t *ksp, void *buf, int rw);
kmutex_t pr_list_kstat_mutex;

/*
 * Limit the number of multiple CE page retires.
 * The default is 0.1% of physmem, or 1 in 1000 pages. This is set in
 * basis points, where 100 basis points equals one percent.
 */
#define MCE_BPT 10
uint64_t        max_pages_retired_bps = MCE_BPT;
#define PAGE_RETIRE_LIMIT       ((physmem * max_pages_retired_bps) / 10000)

/*
 * Control over the verbosity of page retirement.
 *
 * When set to zero (the default), no messages will be printed.
 * When set to one, summary messages will be printed.
 * When set > one, all messages will be printed.
 *
 * A value of one will trigger detailed messages for retirement operations,
 * and is intended as a platform tunable for processors where FMA's DE does
 * not run (e.g., spitfire). Values > one are intended for debugging only.
 */
int page_retire_messages = 0;

/*
 * Control whether or not we return scrubbed UE pages to service.
 * By default we do not since FMA wants to run its diagnostics first
 * and then ask us to unretire the page if it passes. Non-FMA platforms
 * may set this to zero so we will only retire recidivist pages. It should
 * not be changed by the user.
 */
int page_retire_first_ue = 1;

/*
 * Master enable for page retire. This prevents a CE or UE early in boot
 * from trying to retire a page before page_retire_init() has finished
 * setting things up. This is internal only and is not a tunable!
 */
static int pr_enable = 0;

static void (*memscrub_notify_func)(uint64_t);

#ifdef  DEBUG
struct page_retire_debug {
        int prd_dup1;
        int prd_dup2;
        int prd_qdup;
        int prd_noaction;
        int prd_queued;
        int prd_notqueued;
        int prd_dequeue;
        int prd_top;
        int prd_locked;
        int prd_reloc;
        int prd_relocfail;
        int prd_mod;
        int prd_mod_late;
        int prd_kern;
        int prd_free;
        int prd_noreclaim;
        int prd_hashout;
        int prd_fma;
        int prd_uescrubbed;
        int prd_uenotscrubbed;
        int prd_mce;
        int prd_prlocked;
        int prd_prnotlocked;
        int prd_prretired;
        int prd_ulocked;
        int prd_unotretired;
        int prd_udestroy;
        int prd_uhashout;
        int prd_uunretired;
        int prd_unotlocked;
        int prd_checkhit;
        int prd_checkmiss_pend;
        int prd_checkmiss_noerr;
        int prd_tctop;
        int prd_tclocked;
        int prd_hunt;
        int prd_dohunt;
        int prd_earlyhunt;
        int prd_latehunt;
        int prd_nofreedemote;
        int prd_nodemote;
        int prd_demoted;
} pr_debug;

#define PR_DEBUG(foo)   ((pr_debug.foo)++)

/*
 * A type histogram. We record the incidence of the various toxic
 * flag combinations along with the interesting page attributes. The
 * goal is to get as many combinations as we can while driving all
 * pr_debug values nonzero (indicating we've exercised all possible
 * code paths across all possible page types). Not all combinations
 * will make sense -- e.g. PRT_MOD|PRT_KERNEL.
 *
 * pr_type offset bit encoding (when examining with a debugger):
 *
 *    PRT_NAMED  - 0x4
 *    PRT_KERNEL - 0x8
 *    PRT_FREE   - 0x10
 *    PRT_MOD    - 0x20
 *    PRT_FMA    - 0x0
 *    PRT_MCE    - 0x40
 *    PRT_UE     - 0x80
 */

#define PRT_NAMED       0x01
#define PRT_KERNEL      0x02
#define PRT_FREE        0x04
#define PRT_MOD         0x08
#define PRT_FMA         0x00    /* yes, this is not a mistake */
#define PRT_MCE         0x10
#define PRT_UE          0x20
#define PRT_ALL         0x3F

int pr_types[PRT_ALL+1];

#define PR_TYPES(pp)    {                       \
        int whichtype = 0;                      \
        if (pp->p_vnode)                        \
                whichtype |= PRT_NAMED;         \
        if (PP_ISKAS(pp))                       \
                whichtype |= PRT_KERNEL;        \
        if (PP_ISFREE(pp))                      \
                whichtype |= PRT_FREE;          \
        if (hat_ismod(pp))                      \
                whichtype |= PRT_MOD;           \
        if (pp->p_toxic & PR_UE)                \
                whichtype |= PRT_UE;            \
        if (pp->p_toxic & PR_MCE)               \
                whichtype |= PRT_MCE;           \
        pr_types[whichtype]++;                  \
}

int recl_calls;
int recl_mtbf = 3;
int reloc_calls;
int reloc_mtbf = 7;
int pr_calls;
int pr_mtbf = 15;

#define MTBF(v, f)      (((++(v)) & (f)) != (f))

#else   /* DEBUG */

#define PR_DEBUG(foo)   /* nothing */
#define PR_TYPES(foo)   /* nothing */
#define MTBF(v, f)      (1)

#endif  /* DEBUG */

/*
 * page_retire_done() - completion processing
 *
 * Used by the page_retire code for common completion processing.
 * It keeps track of how many times a given result has happened,
 * and writes out an occasional message.
 *
 * May be called with a NULL pp (PRD_INVALID_PA case).
 */
#define PRD_INVALID_KEY         -1
#define PRD_SUCCESS             0
#define PRD_PENDING             1
#define PRD_FAILED              2
#define PRD_DUPLICATE           3
#define PRD_INVALID_PA          4
#define PRD_LIMIT               5
#define PRD_UE_SCRUBBED         6
#define PRD_UNR_SUCCESS         7
#define PRD_UNR_CANTLOCK        8
#define PRD_UNR_NOT             9

typedef struct page_retire_op {
        int     pr_key;         /* one of the PRD_* defines from above */
        int     pr_count;       /* How many times this has happened */
        int     pr_retval;      /* return value */
        int     pr_msglvl;      /* message level - when to print */
        char    *pr_message;    /* Cryptic message for field service */
} page_retire_op_t;

static page_retire_op_t page_retire_ops[] = {
        /* key                  count   retval  msglvl  message */
        {PRD_SUCCESS,           0,      0,      1,
                "Page 0x%08x.%08x removed from service"},
        {PRD_PENDING,           0,      EAGAIN, 2,
                "Page 0x%08x.%08x will be retired on free"},
        {PRD_FAILED,            0,      EAGAIN, 0, NULL},
        {PRD_DUPLICATE,         0,      EIO,    2,
                "Page 0x%08x.%08x already retired or pending"},
        {PRD_INVALID_PA,        0,      EINVAL, 2,
                "PA 0x%08x.%08x is not a relocatable page"},
        {PRD_LIMIT,             0,      0,      1,
                "Page 0x%08x.%08x not retired due to limit exceeded"},
        {PRD_UE_SCRUBBED,       0,      0,      1,
                "Previously reported error on page 0x%08x.%08x cleared"},
        {PRD_UNR_SUCCESS,       0,      0,      1,
                "Page 0x%08x.%08x returned to service"},
        {PRD_UNR_CANTLOCK,      0,      EAGAIN, 2,
                "Page 0x%08x.%08x could not be unretired"},
        {PRD_UNR_NOT,           0,      EIO,    2,
                "Page 0x%08x.%08x is not retired"},
        {PRD_INVALID_KEY,       0,      0,      0, NULL} /* MUST BE LAST! */
};

/*
 * print a message if page_retire_messages is true.
 */
#define PR_MESSAGE(debuglvl, msglvl, msg, pa)                           \
{                                                                       \
        uint64_t p = (uint64_t)pa;                                      \
        if (page_retire_messages >= msglvl && msg != NULL) {            \
                cmn_err(debuglvl, msg,                                  \
                    (uint32_t)(p >> 32), (uint32_t)p);                  \
        }                                                               \
}

/*
 * Note that multiple bits may be set in a single settoxic operation.
 * May be called without the page locked.
 */
void
page_settoxic(page_t *pp, uchar_t bits)
{
        atomic_or_8(&pp->p_toxic, bits);
}

/*
 * Note that multiple bits may cleared in a single clrtoxic operation.
 * Must be called with the page exclusively locked to prevent races which
 * may attempt to retire a page without any toxic bits set.
 * Note that the PR_CAPTURE bit can be cleared without the exclusive lock
 * being held as there is a separate mutex which protects that bit.
 */
void
page_clrtoxic(page_t *pp, uchar_t bits)
{
        ASSERT((bits & PR_CAPTURE) || PAGE_EXCL(pp));
        atomic_and_8(&pp->p_toxic, ~bits);
}

/*
 * Prints any page retire messages to the user, and decides what
 * error code is appropriate for the condition reported.
 */
static int
page_retire_done(page_t *pp, int code)
{
        page_retire_op_t *prop;
        uint64_t        pa = 0;
        int             i;

        if (pp != NULL) {
                pa = mmu_ptob((uint64_t)pp->p_pagenum);
        }

        prop = NULL;
        for (i = 0; page_retire_ops[i].pr_key != PRD_INVALID_KEY; i++) {
                if (page_retire_ops[i].pr_key == code) {
                        prop = &page_retire_ops[i];
                        break;
                }
        }

#ifdef  DEBUG
        if (page_retire_ops[i].pr_key == PRD_INVALID_KEY) {
                cmn_err(CE_PANIC, "page_retire_done: Invalid opcode %d", code);
        }
#endif

        ASSERT(prop->pr_key == code);

        prop->pr_count++;

        PR_MESSAGE(CE_NOTE, prop->pr_msglvl, prop->pr_message, pa);
        if (pp != NULL) {
                page_settoxic(pp, PR_MSG);
        }

        return (prop->pr_retval);
}

/*
 * Act like page_destroy(), but instead of freeing the page, hash it onto
 * the retired_pages vnode, and mark it retired.
 *
 * For fun, we try to scrub the page until it's squeaky clean.
 * availrmem is adjusted here.
 */
static void
page_retire_destroy(page_t *pp)
{
        uoff_t off = (uoff_t)((uintptr_t)pp);

        ASSERT(PAGE_EXCL(pp));
        ASSERT(!PP_ISFREE(pp));
        ASSERT(pp->p_szc == 0);
        ASSERT(!hat_page_is_mapped(pp));
        ASSERT(!pp->p_vnode);

        page_clr_all_props(pp);
        pagescrub(pp, 0, MMU_PAGESIZE);

        pp->p_next = NULL;
        pp->p_prev = NULL;
        if (page_hashin(pp, &retired_pages->v_object, off, false) == 0) {
                cmn_err(CE_PANIC, "retired page %p hashin failed", (void *)pp);
        }

        page_settoxic(pp, PR_RETIRED);
        PR_INCR_KSTAT(pr_retired);

        if (pp->p_toxic & PR_FMA) {
                PR_INCR_KSTAT(pr_fma);
        } else if (pp->p_toxic & PR_UE) {
                PR_INCR_KSTAT(pr_ue);
        } else {
                PR_INCR_KSTAT(pr_mce);
        }

        mutex_enter(&freemem_lock);
        availrmem--;
        mutex_exit(&freemem_lock);

        page_unlock(pp);
}

/*
 * Check whether the number of pages which have been retired already exceeds
 * the maximum allowable percentage of memory which may be retired.
 *
 * Returns 1 if the limit has been exceeded.
 */
static int
page_retire_limit(void)
{
        if (PR_KSTAT_RETIRED_NOTUE >= (uint64_t)PAGE_RETIRE_LIMIT) {
                PR_INCR_KSTAT(pr_limit_exceeded);
                return (1);
        }

        return (0);
}

#define MSG_DM  "Data Mismatch occurred at PA 0x%08x.%08x"              \
        "[ 0x%x != 0x%x ] while attempting to clear previously "        \
        "reported error; page removed from service"

#define MSG_UE  "Uncorrectable Error occurred at PA 0x%08x.%08x while " \
        "attempting to clear previously reported error; page removed "  \
        "from service"

/*
 * Attempt to clear a UE from a page.
 * Returns 1 if the error has been successfully cleared.
 */
static int
page_clear_transient_ue(page_t *pp)
{
        caddr_t         kaddr;
        uint8_t         rb, wb;
        uint64_t        pa;
        uint32_t        pa_hi, pa_lo;
        on_trap_data_t  otd;
        int             errors = 0;
        int             i;

        ASSERT(PAGE_EXCL(pp));
        ASSERT(PP_PR_REQ(pp));
        ASSERT(pp->p_szc == 0);
        ASSERT(!hat_page_is_mapped(pp));

        /*
         * Clear the page and attempt to clear the UE.  If we trap
         * on the next access to the page, we know the UE has recurred.
         */
        pagescrub(pp, 0, PAGESIZE);

        /*
         * Map the page and write a bunch of bit patterns to compare
         * what we wrote with what we read back.  This isn't a perfect
         * test but it should be good enough to catch most of the
         * recurring UEs. If this fails to catch a recurrent UE, we'll
         * retire the page the next time we see a UE on the page.
         */
        kaddr = ppmapin(pp, PROT_READ|PROT_WRITE, (caddr_t)-1);

        pa = ptob((uint64_t)page_pptonum(pp));
        pa_hi = (uint32_t)(pa >> 32);
        pa_lo = (uint32_t)pa;

        /*
         * Disable preemption to prevent the off chance that
         * we migrate while in the middle of running through
         * the bit pattern and run on a different processor
         * than what we started on.
         */
        kpreempt_disable();

        /*
         * Fill the page with each (0x00 - 0xFF] bit pattern, flushing
         * the cache in between reading and writing.  We do this under
         * on_trap() protection to avoid recursion.
         */
        if (on_trap(&otd, OT_DATA_EC)) {
                PR_MESSAGE(CE_WARN, 1, MSG_UE, pa);
                errors = 1;
        } else {
                for (wb = 0xff; wb > 0; wb--) {
                        for (i = 0; i < PAGESIZE; i++) {
                                kaddr[i] = wb;
                        }

                        sync_data_memory(kaddr, PAGESIZE);

                        for (i = 0; i < PAGESIZE; i++) {
                                rb = kaddr[i];
                                if (rb != wb) {
                                        /*
                                         * We had a mismatch without a trap.
                                         * Uh-oh. Something is really wrong
                                         * with this system.
                                         */
                                        if (page_retire_messages) {
                                                cmn_err(CE_WARN, MSG_DM,
                                                    pa_hi, pa_lo, rb, wb);
                                        }
                                        errors = 1;
                                        goto out;       /* double break */
                                }
                        }
                }
        }
out:
        no_trap();
        kpreempt_enable();
        ppmapout(kaddr);

        return (errors ? 0 : 1);
}

/*
 * Try to clear a page_t with a single UE. If the UE was transient, it is
 * returned to service, and we return 1. Otherwise we return 0 meaning
 * that further processing is required to retire the page.
 */
static int
page_retire_transient_ue(page_t *pp)
{
        ASSERT(PAGE_EXCL(pp));
        ASSERT(!hat_page_is_mapped(pp));

        /*
         * If this page is a repeat offender, retire it under the
         * "two strikes and you're out" rule. The caller is responsible
         * for scrubbing the page to try to clear the error.
         */
        if (pp->p_toxic & PR_UE_SCRUBBED) {
                PR_INCR_KSTAT(pr_ue_persistent);
                return (0);
        }

        if (page_clear_transient_ue(pp)) {
                /*
                 * We set the PR_SCRUBBED_UE bit; if we ever see this
                 * page again, we will retire it, no questions asked.
                 */
                page_settoxic(pp, PR_UE_SCRUBBED);

                if (page_retire_first_ue) {
                        PR_INCR_KSTAT(pr_ue_cleared_retire);
                        return (0);
                } else {
                        PR_INCR_KSTAT(pr_ue_cleared_free);

                        page_clrtoxic(pp, PR_UE | PR_MCE | PR_MSG);

                        VN_DISPOSE(pp, B_FREE, 1, kcred);
                        return (1);
                }
        }

        PR_INCR_KSTAT(pr_ue_persistent);
        return (0);
}

/*
 * Update the statistics dynamically when our kstat is read.
 */
static int
page_retire_kstat_update(kstat_t *ksp, int rw)
{
        struct page_retire_kstat *pr;

        if (ksp == NULL)
                return (EINVAL);

        switch (rw) {

        case KSTAT_READ:
                pr = (struct page_retire_kstat *)ksp->ks_data;
                ASSERT(pr == &page_retire_kstat);
                pr->pr_limit.value.ui64 = PAGE_RETIRE_LIMIT;
                return (0);

        case KSTAT_WRITE:
                return (EACCES);

        default:
                return (EINVAL);
        }
        /*NOTREACHED*/
}

static int
pr_list_kstat_update(kstat_t *ksp, int rw)
{
        struct vmobject *obj = &retired_pages->v_object;
        uint_t count;
        page_t *pp;

        if (rw == KSTAT_WRITE)
                return (EACCES);

        vmobject_lock(obj);
        /* Needs to be under a lock so that for loop will work right */
        if (!vn_has_cached_data(retired_pages)) {
                vmobject_unlock(obj);
                ksp->ks_ndata = 0;
                ksp->ks_data_size = 0;
                return (0);
        }

        count = 1;
        for (pp = vmobject_get_next(obj, vmobject_get_head(obj));
            pp != NULL; pp = vmobject_get_next(obj, pp)) {
                count++;
        }
        vmobject_unlock(obj);

        ksp->ks_ndata = count;
        ksp->ks_data_size = count * 2 * sizeof (uint64_t);

        return (0);
}

/*
 * all spans will be pagesize and no coalescing will be done with the
 * list produced.
 */
static int
pr_list_kstat_snapshot(kstat_t *ksp, void *buf, int rw)
{
        struct vmobject *obj = &retired_pages->v_object;
        page_t *pp;
        struct memunit {
                uint64_t address;
                uint64_t size;
        } *kspmem;

        if (rw == KSTAT_WRITE)
                return (EACCES);

        ksp->ks_snaptime = gethrtime();

        kspmem = (struct memunit *)buf;

        vmobject_lock(obj);
        pp = vmobject_get_head(obj);
        if (((caddr_t)kspmem >= (caddr_t)buf + ksp->ks_data_size) ||
            (pp == NULL)) {
                vmobject_unlock(obj);
                return (0);
        }
        kspmem->address = ptob(pp->p_pagenum);
        kspmem->size = PAGESIZE;
        kspmem++;
        for (pp = vmobject_get_next(obj, pp); pp != NULL;
            pp = vmobject_get_next(obj, pp), kspmem++) {
                if ((caddr_t)kspmem >= (caddr_t)buf + ksp->ks_data_size)
                        break;
                kspmem->address = ptob(pp->p_pagenum);
                kspmem->size = PAGESIZE;
        }
        vmobject_unlock(obj);

        return (0);
}

/*
 * page_retire_pend_count -- helper function for page_capture_thread,
 * returns the number of pages pending retirement.
 */
uint64_t
page_retire_pend_count(void)
{
        return (PR_KSTAT_PENDING);
}

uint64_t
page_retire_pend_kas_count(void)
{
        return (PR_KSTAT_PENDING_KAS);
}

void
page_retire_incr_pend_count(void *datap)
{
        PR_INCR_KSTAT(pr_pending);

        if ((datap == &kvp) || (datap == &zvp)) {
                PR_INCR_KSTAT(pr_pending_kas);
        }
}

void
page_retire_decr_pend_count(void *datap)
{
        PR_DECR_KSTAT(pr_pending);

        if ((datap == &kvp) || (datap == &zvp)) {
                PR_DECR_KSTAT(pr_pending_kas);
        }
}

/*
 * Initialize the page retire mechanism:
 *
 *   - Establish the correctable error retire limit.
 *   - Initialize locks.
 *   - Build the retired_pages vnode.
 *   - Set up the kstats.
 *   - Fire off the background thread.
 *   - Tell page_retire() it's OK to start retiring pages.
 */
void
page_retire_init(void)
{
        kstat_t *ksp;

        const uint_t page_retire_ndata =
            sizeof (page_retire_kstat) / sizeof (kstat_named_t);

        ASSERT(page_retire_ksp == NULL);

        if (max_pages_retired_bps <= 0) {
                max_pages_retired_bps = MCE_BPT;
        }

        mutex_init(&pr_q_mutex, NULL, MUTEX_DEFAULT, NULL);

        retired_pages = vn_alloc(KM_SLEEP);
        vn_setops(retired_pages, &retired_vnodeops);

        if ((page_retire_ksp = kstat_create("unix", 0, "page_retire",
            "misc", KSTAT_TYPE_NAMED, page_retire_ndata,
            KSTAT_FLAG_VIRTUAL)) == NULL) {
                cmn_err(CE_WARN, "kstat_create for page_retire failed");
        } else {
                page_retire_ksp->ks_data = (void *)&page_retire_kstat;
                page_retire_ksp->ks_update = page_retire_kstat_update;
                kstat_install(page_retire_ksp);
        }

        mutex_init(&pr_list_kstat_mutex, NULL, MUTEX_DEFAULT, NULL);
        ksp = kstat_create("unix", 0, "page_retire_list", "misc",
            KSTAT_TYPE_RAW, 0, KSTAT_FLAG_VAR_SIZE | KSTAT_FLAG_VIRTUAL);
        if (ksp != NULL) {
                ksp->ks_update = pr_list_kstat_update;
                ksp->ks_snapshot = pr_list_kstat_snapshot;
                ksp->ks_lock = &pr_list_kstat_mutex;
                kstat_install(ksp);
        }

        memscrub_notify_func =
            (void(*)(uint64_t))kobj_getsymvalue("memscrub_notify", 0);

        page_capture_register_callback(PC_RETIRE, -1, page_retire_pp_finish);
        pr_enable = 1;
}

/*
 * page_retire_hunt() callback for the retire thread.
 */
static void
page_retire_thread_cb(page_t *pp)
{
        PR_DEBUG(prd_tctop);
        if (!PP_ISKAS(pp) && page_trylock(pp, SE_EXCL)) {
                PR_DEBUG(prd_tclocked);
                page_unlock(pp);
        }
}

/*
 * Callback used by page_trycapture() to finish off retiring a page.
 * The page has already been cleaned and we've been given sole access to
 * it.
 * Always returns 0 to indicate that callback succeded as the callback never
 * fails to finish retiring the given page.
 */
/*ARGSUSED*/
static int
page_retire_pp_finish(page_t *pp, void *notused, uint_t flags)
{
        int             toxic;

        ASSERT(PAGE_EXCL(pp));
        ASSERT(pp->p_iolock_state == 0);
        ASSERT(pp->p_szc == 0);

        toxic = pp->p_toxic;

        /*
         * The problem page is locked, demoted, unmapped, not free,
         * hashed out, and not COW or mlocked (whew!).
         *
         * Now we select our ammunition, take it around back, and shoot it.
         */
        if (toxic & PR_UE) {
ue_error:
                if (page_retire_transient_ue(pp)) {
                        PR_DEBUG(prd_uescrubbed);
                        (void) page_retire_done(pp, PRD_UE_SCRUBBED);
                } else {
                        PR_DEBUG(prd_uenotscrubbed);
                        page_retire_destroy(pp);
                        (void) page_retire_done(pp, PRD_SUCCESS);
                }
                return (0);
        } else if (toxic & PR_FMA) {
                PR_DEBUG(prd_fma);
                page_retire_destroy(pp);
                (void) page_retire_done(pp, PRD_SUCCESS);
                return (0);
        } else if (toxic & PR_MCE) {
                PR_DEBUG(prd_mce);
                page_retire_destroy(pp);
                (void) page_retire_done(pp, PRD_SUCCESS);
                return (0);
        }

        /*
         * When page_retire_first_ue is set to zero and a UE occurs which is
         * transient, it's possible that we clear some flags set by a second
         * UE error on the page which occurs while the first is currently being
         * handled and thus we need to handle the case where none of the above
         * are set.  In this instance, PR_UE_SCRUBBED should be set and thus
         * we should execute the UE code above.
         */
        if (toxic & PR_UE_SCRUBBED) {
                goto ue_error;
        }

        /*
         * It's impossible to get here.
         */
        panic("bad toxic flags 0x%x in page_retire_pp_finish\n", toxic);
        return (0);
}

/*
 * page_retire() - the front door in to retire a page.
 *
 * Ideally, page_retire() would instantly retire the requested page.
 * Unfortunately, some pages are locked or otherwise tied up and cannot be
 * retired right away.  We use the page capture logic to deal with this
 * situation as it will continuously try to retire the page in the background
 * if the first attempt fails.  Success is determined by looking to see whether
 * the page has been retired after the page_trycapture() attempt.
 *
 * Returns:
 *
 *   - 0 on success,
 *   - EINVAL when the PA is whacko,
 *   - EIO if the page is already retired or already pending retirement, or
 *   - EAGAIN if the page could not be _immediately_ retired but is pending.
 */
int
page_retire(uint64_t pa, uchar_t reason)
{
        page_t  *pp;

        ASSERT(reason & PR_REASONS);            /* there must be a reason */
        ASSERT(!(reason & ~PR_REASONS));        /* but no other bits */

        pp = page_numtopp_nolock(mmu_btop(pa));
        if (pp == NULL) {
                PR_MESSAGE(CE_WARN, 1, "Cannot schedule clearing of error on"
                    " page 0x%08x.%08x; page is not relocatable memory", pa);
                return (page_retire_done(pp, PRD_INVALID_PA));
        }
        if (PP_RETIRED(pp)) {
                PR_DEBUG(prd_dup1);
                return (page_retire_done(pp, PRD_DUPLICATE));
        }

        if (memscrub_notify_func != NULL) {
                (void) memscrub_notify_func(pa);
        }

        if ((reason & PR_UE) && !PP_TOXIC(pp)) {
                PR_MESSAGE(CE_NOTE, 1, "Scheduling clearing of error on"
                    " page 0x%08x.%08x", pa);
        } else if (PP_PR_REQ(pp)) {
                PR_DEBUG(prd_dup2);
                return (page_retire_done(pp, PRD_DUPLICATE));
        } else {
                PR_MESSAGE(CE_NOTE, 1, "Scheduling removal of"
                    " page 0x%08x.%08x", pa);
        }

        /* Avoid setting toxic bits in the first place */
        if ((reason & (PR_FMA | PR_MCE)) && !(reason & PR_UE) &&
            page_retire_limit()) {
                return (page_retire_done(pp, PRD_LIMIT));
        }

        if (MTBF(pr_calls, pr_mtbf)) {
                page_settoxic(pp, reason);
                if (page_trycapture(pp, 0, CAPTURE_RETIRE, pp->p_vnode) == 0) {
                        PR_DEBUG(prd_prlocked);
                } else {
                        PR_DEBUG(prd_prnotlocked);
                }
        } else {
                PR_DEBUG(prd_prnotlocked);
        }

        if (PP_RETIRED(pp)) {
                PR_DEBUG(prd_prretired);
                return (0);
        } else {
                cv_signal(&pc_cv);
                PR_INCR_KSTAT(pr_failed);

                if (pp->p_toxic & PR_MSG) {
                        return (page_retire_done(pp, PRD_FAILED));
                } else {
                        return (page_retire_done(pp, PRD_PENDING));
                }
        }
}

/*
 * Take a retired page off the retired-pages vnode and clear the toxic flags.
 * If "free" is nonzero, lock it and put it back on the freelist. If "free"
 * is zero, the caller already holds SE_EXCL lock so we simply unretire it
 * and don't do anything else with it.
 *
 * Any unretire messages are printed from this routine.
 *
 * Returns 0 if page pp was unretired; else an error code.
 *
 * If flags is:
 *      PR_UNR_FREE - lock the page, clear the toxic flags and free it
 *          to the freelist.
 *      PR_UNR_TEMP - lock the page, unretire it, leave the toxic
 *          bits set as is and return it to the caller.
 *      PR_UNR_CLEAN - page is SE_EXCL locked, unretire it, clear the
 *          toxic flags and return it to caller as is.
 */
int
page_unretire_pp(page_t *pp, int flags)
{
        /*
         * To be retired, a page has to be hashed onto the retired_pages vnode
         * and have PR_RETIRED set in p_toxic.
         */
        if (flags == PR_UNR_CLEAN ||
            page_try_reclaim_lock(pp, SE_EXCL, SE_RETIRED)) {
                ASSERT(PAGE_EXCL(pp));
                PR_DEBUG(prd_ulocked);
                if (!PP_RETIRED(pp)) {
                        PR_DEBUG(prd_unotretired);
                        page_unlock(pp);
                        return (page_retire_done(pp, PRD_UNR_NOT));
                }

                PR_MESSAGE(CE_NOTE, 1, "unretiring retired"
                    " page 0x%08x.%08x", mmu_ptob((uint64_t)pp->p_pagenum));
                if (pp->p_toxic & PR_FMA) {
                        PR_DECR_KSTAT(pr_fma);
                } else if (pp->p_toxic & PR_UE) {
                        PR_DECR_KSTAT(pr_ue);
                } else {
                        PR_DECR_KSTAT(pr_mce);
                }

                if (flags == PR_UNR_TEMP)
                        page_clrtoxic(pp, PR_RETIRED);
                else
                        page_clrtoxic(pp, PR_TOXICFLAGS);

                if (flags == PR_UNR_FREE) {
                        PR_DEBUG(prd_udestroy);
                        page_destroy(pp, 0);
                } else {
                        PR_DEBUG(prd_uhashout);
                        page_hashout(pp, false);
                }

                mutex_enter(&freemem_lock);
                availrmem++;
                mutex_exit(&freemem_lock);

                PR_DEBUG(prd_uunretired);
                PR_DECR_KSTAT(pr_retired);
                PR_INCR_KSTAT(pr_unretired);
                return (page_retire_done(pp, PRD_UNR_SUCCESS));
        }
        PR_DEBUG(prd_unotlocked);
        return (page_retire_done(pp, PRD_UNR_CANTLOCK));
}

/*
 * Return a page to service by moving it from the retired_pages vnode
 * onto the freelist.
 *
 * Called from mmioctl_page_retire() on behalf of the FMA DE.
 *
 * Returns:
 *
 *   - 0 if the page is unretired,
 *   - EAGAIN if the pp can not be locked,
 *   - EINVAL if the PA is whacko, and
 *   - EIO if the pp is not retired.
 */
int
page_unretire(uint64_t pa)
{
        page_t  *pp;

        pp = page_numtopp_nolock(mmu_btop(pa));
        if (pp == NULL) {
                return (page_retire_done(pp, PRD_INVALID_PA));
        }

        return (page_unretire_pp(pp, PR_UNR_FREE));
}

/*
 * Test a page to see if it is retired. If errors is non-NULL, the toxic
 * bits of the page are returned. Returns 0 on success, error code on failure.
 */
int
page_retire_check_pp(page_t *pp, uint64_t *errors)
{
        int rc;

        if (PP_RETIRED(pp)) {
                PR_DEBUG(prd_checkhit);
                rc = 0;
        } else if (PP_PR_REQ(pp)) {
                PR_DEBUG(prd_checkmiss_pend);
                rc = EAGAIN;
        } else {
                PR_DEBUG(prd_checkmiss_noerr);
                rc = EIO;
        }

        /*
         * We have magically arranged the bit values returned to fmd(8)
         * to line up with the FMA, MCE, and UE bits of the page_t.
         */
        if (errors) {
                uint64_t toxic = (uint64_t)(pp->p_toxic & PR_ERRMASK);
                if (toxic & PR_UE_SCRUBBED) {
                        toxic &= ~PR_UE_SCRUBBED;
                        toxic |= PR_UE;
                }
                *errors = toxic;
        }

        return (rc);
}

/*
 * Test to see if the page_t for a given PA is retired, and return the
 * hardware errors we have seen on the page if requested.
 *
 * Called from mmioctl_page_retire on behalf of the FMA DE.
 *
 * Returns:
 *
 *   - 0 if the page is retired,
 *   - EIO if the page is not retired and has no errors,
 *   - EAGAIN if the page is not retired but is pending; and
 *   - EINVAL if the PA is whacko.
 */
int
page_retire_check(uint64_t pa, uint64_t *errors)
{
        page_t  *pp;

        if (errors) {
                *errors = 0;
        }

        pp = page_numtopp_nolock(mmu_btop(pa));
        if (pp == NULL) {
                return (page_retire_done(pp, PRD_INVALID_PA));
        }

        return (page_retire_check_pp(pp, errors));
}

/*
 * Page retire self-test. For now, it always returns 0.
 */
int
page_retire_test(void)
{
        page_t *first, *pp, *cpp, *cpp2, *lpp;

        /*
         * Tests the corner case where a large page can't be retired
         * because one of the constituent pages is locked. We mark
         * one page to be retired and try to retire it, and mark the
         * other page to be retired but don't try to retire it, so
         * that page_unlock() in the failure path will recurse and try
         * to retire THAT page. This is the worst possible situation
         * we can get ourselves into.
         */
        memsegs_lock(0);
        pp = first = page_first();
        do {
                if (pp->p_szc && PP_PAGEROOT(pp) == pp) {
                        cpp = pp + 1;
                        lpp = PP_ISFREE(pp)? pp : pp + 2;
                        cpp2 = pp + 3;
                        if (!page_trylock(lpp, pp == lpp? SE_EXCL : SE_SHARED))
                                continue;
                        if (!page_trylock(cpp, SE_EXCL)) {
                                page_unlock(lpp);
                                continue;
                        }

                        /* fails */
                        (void) page_retire(ptob(cpp->p_pagenum), PR_FMA);

                        page_unlock(lpp);
                        page_unlock(cpp);
                        (void) page_retire(ptob(cpp->p_pagenum), PR_FMA);
                        (void) page_retire(ptob(cpp2->p_pagenum), PR_FMA);
                }
        } while ((pp = page_next(pp)) != first);
        memsegs_unlock(0);

        return (0);
}