5045 use atomic_{inc,dec}_* instead of atomic_add_*

[illumos-gate.git] / usr / src / uts / i86pc / vm / htable.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 (c) 2004, 2010, Oracle and/or its affiliates. All rights reserved.
 */

#include <sys/types.h>
#include <sys/sysmacros.h>
#include <sys/kmem.h>
#include <sys/atomic.h>
#include <sys/bitmap.h>
#include <sys/machparam.h>
#include <sys/machsystm.h>
#include <sys/mman.h>
#include <sys/systm.h>
#include <sys/cpuvar.h>
#include <sys/thread.h>
#include <sys/proc.h>
#include <sys/cpu.h>
#include <sys/kmem.h>
#include <sys/disp.h>
#include <sys/vmem.h>
#include <sys/vmsystm.h>
#include <sys/promif.h>
#include <sys/var.h>
#include <sys/x86_archext.h>
#include <sys/archsystm.h>
#include <sys/bootconf.h>
#include <sys/dumphdr.h>
#include <vm/seg_kmem.h>
#include <vm/seg_kpm.h>
#include <vm/hat.h>
#include <vm/hat_i86.h>
#include <sys/cmn_err.h>
#include <sys/panic.h>

#ifdef __xpv
#include <sys/hypervisor.h>
#include <sys/xpv_panic.h>
#endif

#include <sys/bootinfo.h>
#include <vm/kboot_mmu.h>

static void x86pte_zero(htable_t *dest, uint_t entry, uint_t count);

kmem_cache_t *htable_cache;

/*
 * The variable htable_reserve_amount, rather than HTABLE_RESERVE_AMOUNT,
 * is used in order to facilitate testing of the htable_steal() code.
 * By resetting htable_reserve_amount to a lower value, we can force
 * stealing to occur.  The reserve amount is a guess to get us through boot.
 */
#define HTABLE_RESERVE_AMOUNT   (200)
uint_t htable_reserve_amount = HTABLE_RESERVE_AMOUNT;
kmutex_t htable_reserve_mutex;
uint_t htable_reserve_cnt;
htable_t *htable_reserve_pool;

/*
 * Used to hand test htable_steal().
 */
#ifdef DEBUG
ulong_t force_steal = 0;
ulong_t ptable_cnt = 0;
#endif

/*
 * This variable is so that we can tune this via /etc/system
 * Any value works, but a power of two <= mmu.ptes_per_table is best.
 */
uint_t htable_steal_passes = 8;

/*
 * mutex stuff for access to htable hash
 */
#define NUM_HTABLE_MUTEX 128
kmutex_t htable_mutex[NUM_HTABLE_MUTEX];
#define HTABLE_MUTEX_HASH(h) ((h) & (NUM_HTABLE_MUTEX - 1))

#define HTABLE_ENTER(h) mutex_enter(&htable_mutex[HTABLE_MUTEX_HASH(h)]);
#define HTABLE_EXIT(h)  mutex_exit(&htable_mutex[HTABLE_MUTEX_HASH(h)]);

/*
 * forward declarations
 */
static void link_ptp(htable_t *higher, htable_t *new, uintptr_t vaddr);
static void unlink_ptp(htable_t *higher, htable_t *old, uintptr_t vaddr);
static void htable_free(htable_t *ht);
static x86pte_t *x86pte_access_pagetable(htable_t *ht, uint_t index);
static void x86pte_release_pagetable(htable_t *ht);
static x86pte_t x86pte_cas(htable_t *ht, uint_t entry, x86pte_t old,
        x86pte_t new);

/*
 * A counter to track if we are stealing or reaping htables. When non-zero
 * htable_free() will directly free htables (either to the reserve or kmem)
 * instead of putting them in a hat's htable cache.
 */
uint32_t htable_dont_cache = 0;

/*
 * Track the number of active pagetables, so we can know how many to reap
 */
static uint32_t active_ptables = 0;

#ifdef __xpv
/*
 * Deal with hypervisor complications.
 */
void
xen_flush_va(caddr_t va)
{
        struct mmuext_op t;
        uint_t count;

        if (IN_XPV_PANIC()) {
                mmu_tlbflush_entry((caddr_t)va);
        } else {
                t.cmd = MMUEXT_INVLPG_LOCAL;
                t.arg1.linear_addr = (uintptr_t)va;
                if (HYPERVISOR_mmuext_op(&t, 1, &count, DOMID_SELF) < 0)
                        panic("HYPERVISOR_mmuext_op() failed");
                ASSERT(count == 1);
        }
}

void
xen_gflush_va(caddr_t va, cpuset_t cpus)
{
        struct mmuext_op t;
        uint_t count;

        if (IN_XPV_PANIC()) {
                mmu_tlbflush_entry((caddr_t)va);
                return;
        }

        t.cmd = MMUEXT_INVLPG_MULTI;
        t.arg1.linear_addr = (uintptr_t)va;
        /*LINTED: constant in conditional context*/
        set_xen_guest_handle(t.arg2.vcpumask, &cpus);
        if (HYPERVISOR_mmuext_op(&t, 1, &count, DOMID_SELF) < 0)
                panic("HYPERVISOR_mmuext_op() failed");
        ASSERT(count == 1);
}

void
xen_flush_tlb()
{
        struct mmuext_op t;
        uint_t count;

        if (IN_XPV_PANIC()) {
                xpv_panic_reload_cr3();
        } else {
                t.cmd = MMUEXT_TLB_FLUSH_LOCAL;
                if (HYPERVISOR_mmuext_op(&t, 1, &count, DOMID_SELF) < 0)
                        panic("HYPERVISOR_mmuext_op() failed");
                ASSERT(count == 1);
        }
}

void
xen_gflush_tlb(cpuset_t cpus)
{
        struct mmuext_op t;
        uint_t count;

        ASSERT(!IN_XPV_PANIC());
        t.cmd = MMUEXT_TLB_FLUSH_MULTI;
        /*LINTED: constant in conditional context*/
        set_xen_guest_handle(t.arg2.vcpumask, &cpus);
        if (HYPERVISOR_mmuext_op(&t, 1, &count, DOMID_SELF) < 0)
                panic("HYPERVISOR_mmuext_op() failed");
        ASSERT(count == 1);
}

/*
 * Install/Adjust a kpm mapping under the hypervisor.
 * Value of "how" should be:
 *      PT_WRITABLE | PT_VALID - regular kpm mapping
 *      PT_VALID - make mapping read-only
 *      0       - remove mapping
 *
 * returns 0 on success. non-zero for failure.
 */
int
xen_kpm_page(pfn_t pfn, uint_t how)
{
        paddr_t pa = mmu_ptob((paddr_t)pfn);
        x86pte_t pte = PT_NOCONSIST | PT_REF | PT_MOD;

        if (kpm_vbase == NULL)
                return (0);

        if (how)
                pte |= pa_to_ma(pa) | how;
        else
                pte = 0;
        return (HYPERVISOR_update_va_mapping((uintptr_t)kpm_vbase + pa,
            pte, UVMF_INVLPG | UVMF_ALL));
}

void
xen_pin(pfn_t pfn, level_t lvl)
{
        struct mmuext_op t;
        uint_t count;

        t.cmd = MMUEXT_PIN_L1_TABLE + lvl;
        t.arg1.mfn = pfn_to_mfn(pfn);
        if (HYPERVISOR_mmuext_op(&t, 1, &count, DOMID_SELF) < 0)
                panic("HYPERVISOR_mmuext_op() failed");
        ASSERT(count == 1);
}

void
xen_unpin(pfn_t pfn)
{
        struct mmuext_op t;
        uint_t count;

        t.cmd = MMUEXT_UNPIN_TABLE;
        t.arg1.mfn = pfn_to_mfn(pfn);
        if (HYPERVISOR_mmuext_op(&t, 1, &count, DOMID_SELF) < 0)
                panic("HYPERVISOR_mmuext_op() failed");
        ASSERT(count == 1);
}

static void
xen_map(uint64_t pte, caddr_t va)
{
        if (HYPERVISOR_update_va_mapping((uintptr_t)va, pte,
            UVMF_INVLPG | UVMF_LOCAL))
                panic("HYPERVISOR_update_va_mapping() failed");
}
#endif /* __xpv */

/*
 * Allocate a memory page for a hardware page table.
 *
 * A wrapper around page_get_physical(), with some extra checks.
 */
static pfn_t
ptable_alloc(uintptr_t seed)
{
        pfn_t pfn;
        page_t *pp;

        pfn = PFN_INVALID;

        /*
         * The first check is to see if there is memory in the system. If we
         * drop to throttlefree, then fail the ptable_alloc() and let the
         * stealing code kick in. Note that we have to do this test here,
         * since the test in page_create_throttle() would let the NOSLEEP
         * allocation go through and deplete the page reserves.
         *
         * The !NOMEMWAIT() lets pageout, fsflush, etc. skip this check.
         */
        if (!NOMEMWAIT() && freemem <= throttlefree + 1)
                return (PFN_INVALID);

#ifdef DEBUG
        /*
         * This code makes htable_steal() easier to test. By setting
         * force_steal we force pagetable allocations to fall
         * into the stealing code. Roughly 1 in ever "force_steal"
         * page table allocations will fail.
         */
        if (proc_pageout != NULL && force_steal > 1 &&
            ++ptable_cnt > force_steal) {
                ptable_cnt = 0;
                return (PFN_INVALID);
        }
#endif /* DEBUG */

        pp = page_get_physical(seed);
        if (pp == NULL)
                return (PFN_INVALID);
        ASSERT(PAGE_SHARED(pp));
        pfn = pp->p_pagenum;
        if (pfn == PFN_INVALID)
                panic("ptable_alloc(): Invalid PFN!!");
        atomic_inc_32(&active_ptables);
        HATSTAT_INC(hs_ptable_allocs);
        return (pfn);
}

/*
 * Free an htable's associated page table page.  See the comments
 * for ptable_alloc().
 */
static void
ptable_free(pfn_t pfn)
{
        page_t *pp = page_numtopp_nolock(pfn);

        /*
         * need to destroy the page used for the pagetable
         */
        ASSERT(pfn != PFN_INVALID);
        HATSTAT_INC(hs_ptable_frees);
        atomic_dec_32(&active_ptables);
        if (pp == NULL)
                panic("ptable_free(): no page for pfn!");
        ASSERT(PAGE_SHARED(pp));
        ASSERT(pfn == pp->p_pagenum);
        ASSERT(!IN_XPV_PANIC());

        /*
         * Get an exclusive lock, might have to wait for a kmem reader.
         */
        if (!page_tryupgrade(pp)) {
                u_offset_t off = pp->p_offset;
                page_unlock(pp);
                pp = page_lookup(&kvp, off, SE_EXCL);
                if (pp == NULL)
                        panic("page not found");
        }
#ifdef __xpv
        if (kpm_vbase && xen_kpm_page(pfn, PT_VALID | PT_WRITABLE) < 0)
                panic("failure making kpm r/w pfn=0x%lx", pfn);
#endif
        page_hashout(pp, NULL);
        page_free(pp, 1);
        page_unresv(1);
}

/*
 * Put one htable on the reserve list.
 */
static void
htable_put_reserve(htable_t *ht)
{
        ht->ht_hat = NULL;              /* no longer tied to a hat */
        ASSERT(ht->ht_pfn == PFN_INVALID);
        HATSTAT_INC(hs_htable_rputs);
        mutex_enter(&htable_reserve_mutex);
        ht->ht_next = htable_reserve_pool;
        htable_reserve_pool = ht;
        ++htable_reserve_cnt;
        mutex_exit(&htable_reserve_mutex);
}

/*
 * Take one htable from the reserve.
 */
static htable_t *
htable_get_reserve(void)
{
        htable_t *ht = NULL;

        mutex_enter(&htable_reserve_mutex);
        if (htable_reserve_cnt != 0) {
                ht = htable_reserve_pool;
                ASSERT(ht != NULL);
                ASSERT(ht->ht_pfn == PFN_INVALID);
                htable_reserve_pool = ht->ht_next;
                --htable_reserve_cnt;
                HATSTAT_INC(hs_htable_rgets);
        }
        mutex_exit(&htable_reserve_mutex);
        return (ht);
}

/*
 * Allocate initial htables and put them on the reserve list
 */
void
htable_initial_reserve(uint_t count)
{
        htable_t *ht;

        count += HTABLE_RESERVE_AMOUNT;
        while (count > 0) {
                ht = kmem_cache_alloc(htable_cache, KM_NOSLEEP);
                ASSERT(ht != NULL);

                ASSERT(use_boot_reserve);
                ht->ht_pfn = PFN_INVALID;
                htable_put_reserve(ht);
                --count;
        }
}

/*
 * Readjust the reserves after a thread finishes using them.
 */
void
htable_adjust_reserve()
{
        htable_t *ht;

        /*
         * Free any excess htables in the reserve list
         */
        while (htable_reserve_cnt > htable_reserve_amount &&
            !USE_HAT_RESERVES()) {
                ht = htable_get_reserve();
                if (ht == NULL)
                        return;
                ASSERT(ht->ht_pfn == PFN_INVALID);
                kmem_cache_free(htable_cache, ht);
        }
}


/*
 * This routine steals htables from user processes for htable_alloc() or
 * for htable_reap().
 */
static htable_t *
htable_steal(uint_t cnt)
{
        hat_t           *hat = kas.a_hat;       /* list starts with khat */
        htable_t        *list = NULL;
        htable_t        *ht;
        htable_t        *higher;
        uint_t          h;
        uint_t          h_start;
        static uint_t   h_seed = 0;
        uint_t          e;
        uintptr_t       va;
        x86pte_t        pte;
        uint_t          stolen = 0;
        uint_t          pass;
        uint_t          threshold;

        /*
         * Limit htable_steal_passes to something reasonable
         */
        if (htable_steal_passes == 0)
                htable_steal_passes = 1;
        if (htable_steal_passes > mmu.ptes_per_table)
                htable_steal_passes = mmu.ptes_per_table;

        /*
         * Loop through all user hats. The 1st pass takes cached htables that
         * aren't in use. The later passes steal by removing mappings, too.
         */
        atomic_inc_32(&htable_dont_cache);
        for (pass = 0; pass <= htable_steal_passes && stolen < cnt; ++pass) {
                threshold = pass * mmu.ptes_per_table / htable_steal_passes;
                hat = kas.a_hat;
                for (;;) {

                        /*
                         * Clear the victim flag and move to next hat
                         */
                        mutex_enter(&hat_list_lock);
                        if (hat != kas.a_hat) {
                                hat->hat_flags &= ~HAT_VICTIM;
                                cv_broadcast(&hat_list_cv);
                        }
                        hat = hat->hat_next;

                        /*
                         * Skip any hat that is already being stolen from.
                         *
                         * We skip SHARED hats, as these are dummy
                         * hats that host ISM shared page tables.
                         *
                         * We also skip if HAT_FREEING because hat_pte_unmap()
                         * won't zero out the PTE's. That would lead to hitting
                         * stale PTEs either here or under hat_unload() when we
                         * steal and unload the same page table in competing
                         * threads.
                         */
                        while (hat != NULL &&
                            (hat->hat_flags &
                            (HAT_VICTIM | HAT_SHARED | HAT_FREEING)) != 0)
                                hat = hat->hat_next;

                        if (hat == NULL) {
                                mutex_exit(&hat_list_lock);
                                break;
                        }

                        /*
                         * Are we finished?
                         */
                        if (stolen == cnt) {
                                /*
                                 * Try to spread the pain of stealing,
                                 * move victim HAT to the end of the HAT list.
                                 */
                                if (pass >= 1 && cnt == 1 &&
                                    kas.a_hat->hat_prev != hat) {

                                        /* unlink victim hat */
                                        if (hat->hat_prev)
                                                hat->hat_prev->hat_next =
                                                    hat->hat_next;
                                        else
                                                kas.a_hat->hat_next =
                                                    hat->hat_next;
                                        if (hat->hat_next)
                                                hat->hat_next->hat_prev =
                                                    hat->hat_prev;
                                        else
                                                kas.a_hat->hat_prev =
                                                    hat->hat_prev;


                                        /* relink at end of hat list */
                                        hat->hat_next = NULL;
                                        hat->hat_prev = kas.a_hat->hat_prev;
                                        if (hat->hat_prev)
                                                hat->hat_prev->hat_next = hat;
                                        else
                                                kas.a_hat->hat_next = hat;
                                        kas.a_hat->hat_prev = hat;

                                }

                                mutex_exit(&hat_list_lock);
                                break;
                        }

                        /*
                         * Mark the HAT as a stealing victim.
                         */
                        hat->hat_flags |= HAT_VICTIM;
                        mutex_exit(&hat_list_lock);

                        /*
                         * Take any htables from the hat's cached "free" list.
                         */
                        hat_enter(hat);
                        while ((ht = hat->hat_ht_cached) != NULL &&
                            stolen < cnt) {
                                hat->hat_ht_cached = ht->ht_next;
                                ht->ht_next = list;
                                list = ht;
                                ++stolen;
                        }
                        hat_exit(hat);

                        /*
                         * Don't steal on first pass.
                         */
                        if (pass == 0 || stolen == cnt)
                                continue;

                        /*
                         * Search the active htables for one to steal.
                         * Start at a different hash bucket every time to
                         * help spread the pain of stealing.
                         */
                        h = h_start = h_seed++ % hat->hat_num_hash;
                        do {
                                higher = NULL;
                                HTABLE_ENTER(h);
                                for (ht = hat->hat_ht_hash[h]; ht;
                                    ht = ht->ht_next) {

                                        /*
                                         * Can we rule out reaping?
                                         */
                                        if (ht->ht_busy != 0 ||
                                            (ht->ht_flags & HTABLE_SHARED_PFN)||
                                            ht->ht_level > 0 ||
                                            ht->ht_valid_cnt > threshold ||
                                            ht->ht_lock_cnt != 0)
                                                continue;

                                        /*
                                         * Increment busy so the htable can't
                                         * disappear. We drop the htable mutex
                                         * to avoid deadlocks with
                                         * hat_pageunload() and the hment mutex
                                         * while we call hat_pte_unmap()
                                         */
                                        ++ht->ht_busy;
                                        HTABLE_EXIT(h);

                                        /*
                                         * Try stealing.
                                         * - unload and invalidate all PTEs
                                         */
                                        for (e = 0, va = ht->ht_vaddr;
                                            e < HTABLE_NUM_PTES(ht) &&
                                            ht->ht_valid_cnt > 0 &&
                                            ht->ht_busy == 1 &&
                                            ht->ht_lock_cnt == 0;
                                            ++e, va += MMU_PAGESIZE) {
                                                pte = x86pte_get(ht, e);
                                                if (!PTE_ISVALID(pte))
                                                        continue;
                                                hat_pte_unmap(ht, e,
                                                    HAT_UNLOAD, pte, NULL);
                                        }

                                        /*
                                         * Reacquire htable lock. If we didn't
                                         * remove all mappings in the table,
                                         * or another thread added a new mapping
                                         * behind us, give up on this table.
                                         */
                                        HTABLE_ENTER(h);
                                        if (ht->ht_busy != 1 ||
                                            ht->ht_valid_cnt != 0 ||
                                            ht->ht_lock_cnt != 0) {
                                                --ht->ht_busy;
                                                continue;
                                        }

                                        /*
                                         * Steal it and unlink the page table.
                                         */
                                        higher = ht->ht_parent;
                                        unlink_ptp(higher, ht, ht->ht_vaddr);

                                        /*
                                         * remove from the hash list
                                         */
                                        if (ht->ht_next)
                                                ht->ht_next->ht_prev =
                                                    ht->ht_prev;

                                        if (ht->ht_prev) {
                                                ht->ht_prev->ht_next =
                                                    ht->ht_next;
                                        } else {
                                                ASSERT(hat->hat_ht_hash[h] ==
                                                    ht);
                                                hat->hat_ht_hash[h] =
                                                    ht->ht_next;
                                        }

                                        /*
                                         * Break to outer loop to release the
                                         * higher (ht_parent) pagetable. This
                                         * spreads out the pain caused by
                                         * pagefaults.
                                         */
                                        ht->ht_next = list;
                                        list = ht;
                                        ++stolen;
                                        break;
                                }
                                HTABLE_EXIT(h);
                                if (higher != NULL)
                                        htable_release(higher);
                                if (++h == hat->hat_num_hash)
                                        h = 0;
                        } while (stolen < cnt && h != h_start);
                }
        }
        atomic_dec_32(&htable_dont_cache);
        return (list);
}

/*
 * This is invoked from kmem when the system is low on memory.  We try
 * to free hments, htables, and ptables to improve the memory situation.
 */
/*ARGSUSED*/
static void
htable_reap(void *handle)
{
        uint_t          reap_cnt;
        htable_t        *list;
        htable_t        *ht;

        HATSTAT_INC(hs_reap_attempts);
        if (!can_steal_post_boot)
                return;

        /*
         * Try to reap 5% of the page tables bounded by a maximum of
         * 5% of physmem and a minimum of 10.
         */
        reap_cnt = MAX(MIN(physmem / 20, active_ptables / 20), 10);

        /*
         * Let htable_steal() do the work, we just call htable_free()
         */
        XPV_DISALLOW_MIGRATE();
        list = htable_steal(reap_cnt);
        XPV_ALLOW_MIGRATE();
        while ((ht = list) != NULL) {
                list = ht->ht_next;
                HATSTAT_INC(hs_reaped);
                htable_free(ht);
        }

        /*
         * Free up excess reserves
         */
        htable_adjust_reserve();
        hment_adjust_reserve();
}

/*
 * Allocate an htable, stealing one or using the reserve if necessary
 */
static htable_t *
htable_alloc(
        hat_t           *hat,
        uintptr_t       vaddr,
        level_t         level,
        htable_t        *shared)
{
        htable_t        *ht = NULL;
        uint_t          is_vlp;
        uint_t          is_bare = 0;
        uint_t          need_to_zero = 1;
        int             kmflags = (can_steal_post_boot ? KM_NOSLEEP : KM_SLEEP);

        if (level < 0 || level > TOP_LEVEL(hat))
                panic("htable_alloc(): level %d out of range\n", level);

        is_vlp = (hat->hat_flags & HAT_VLP) && level == VLP_LEVEL;
        if (is_vlp || shared != NULL)
                is_bare = 1;

        /*
         * First reuse a cached htable from the hat_ht_cached field, this
         * avoids unnecessary trips through kmem/page allocators.
         */
        if (hat->hat_ht_cached != NULL && !is_bare) {
                hat_enter(hat);
                ht = hat->hat_ht_cached;
                if (ht != NULL) {
                        hat->hat_ht_cached = ht->ht_next;
                        need_to_zero = 0;
                        /* XX64 ASSERT() they're all zero somehow */
                        ASSERT(ht->ht_pfn != PFN_INVALID);
                }
                hat_exit(hat);
        }

        if (ht == NULL) {
                /*
                 * Allocate an htable, possibly refilling the reserves.
                 */
                if (USE_HAT_RESERVES()) {
                        ht = htable_get_reserve();
                } else {
                        /*
                         * Donate successful htable allocations to the reserve.
                         */
                        for (;;) {
                                ht = kmem_cache_alloc(htable_cache, kmflags);
                                if (ht == NULL)
                                        break;
                                ht->ht_pfn = PFN_INVALID;
                                if (USE_HAT_RESERVES() ||
                                    htable_reserve_cnt >= htable_reserve_amount)
                                        break;
                                htable_put_reserve(ht);
                        }
                }

                /*
                 * allocate a page for the hardware page table if needed
                 */
                if (ht != NULL && !is_bare) {
                        ht->ht_hat = hat;
                        ht->ht_pfn = ptable_alloc((uintptr_t)ht);
                        if (ht->ht_pfn == PFN_INVALID) {
                                if (USE_HAT_RESERVES())
                                        htable_put_reserve(ht);
                                else
                                        kmem_cache_free(htable_cache, ht);
                                ht = NULL;
                        }
                }
        }

        /*
         * If allocations failed, kick off a kmem_reap() and resort to
         * htable steal(). We may spin here if the system is very low on
         * memory. If the kernel itself has consumed all memory and kmem_reap()
         * can't free up anything, then we'll really get stuck here.
         * That should only happen in a system where the administrator has
         * misconfigured VM parameters via /etc/system.
         */
        while (ht == NULL && can_steal_post_boot) {
                kmem_reap();
                ht = htable_steal(1);
                HATSTAT_INC(hs_steals);

                /*
                 * If we stole for a bare htable, release the pagetable page.
                 */
                if (ht != NULL) {
                        if (is_bare) {
                                ptable_free(ht->ht_pfn);
                                ht->ht_pfn = PFN_INVALID;
#if defined(__xpv) && defined(__amd64)
                        /*
                         * make stolen page table writable again in kpm
                         */
                        } else if (kpm_vbase && xen_kpm_page(ht->ht_pfn,
                            PT_VALID | PT_WRITABLE) < 0) {
                                panic("failure making kpm r/w pfn=0x%lx",
                                    ht->ht_pfn);
#endif
                        }
                }
        }

        /*
         * All attempts to allocate or steal failed. This should only happen
         * if we run out of memory during boot, due perhaps to a huge
         * boot_archive. At this point there's no way to continue.
         */
        if (ht == NULL)
                panic("htable_alloc(): couldn't steal\n");

#if defined(__amd64) && defined(__xpv)
        /*
         * Under the 64-bit hypervisor, we have 2 top level page tables.
         * If this allocation fails, we'll resort to stealing.
         * We use the stolen page indirectly, by freeing the
         * stolen htable first.
         */
        if (level == mmu.max_level) {
                for (;;) {
                        htable_t *stolen;

                        hat->hat_user_ptable = ptable_alloc((uintptr_t)ht + 1);
                        if (hat->hat_user_ptable != PFN_INVALID)
                                break;
                        stolen = htable_steal(1);
                        if (stolen == NULL)
                                panic("2nd steal ptable failed\n");
                        htable_free(stolen);
                }
                block_zero_no_xmm(kpm_vbase + pfn_to_pa(hat->hat_user_ptable),
                    MMU_PAGESIZE);
        }
#endif

        /*
         * Shared page tables have all entries locked and entries may not
         * be added or deleted.
         */
        ht->ht_flags = 0;
        if (shared != NULL) {
                ASSERT(shared->ht_valid_cnt > 0);
                ht->ht_flags |= HTABLE_SHARED_PFN;
                ht->ht_pfn = shared->ht_pfn;
                ht->ht_lock_cnt = 0;
                ht->ht_valid_cnt = 0;           /* updated in hat_share() */
                ht->ht_shares = shared;
                need_to_zero = 0;
        } else {
                ht->ht_shares = NULL;
                ht->ht_lock_cnt = 0;
                ht->ht_valid_cnt = 0;
        }

        /*
         * setup flags, etc. for VLP htables
         */
        if (is_vlp) {
                ht->ht_flags |= HTABLE_VLP;
                ASSERT(ht->ht_pfn == PFN_INVALID);
                need_to_zero = 0;
        }

        /*
         * fill in the htable
         */
        ht->ht_hat = hat;
        ht->ht_parent = NULL;
        ht->ht_vaddr = vaddr;
        ht->ht_level = level;
        ht->ht_busy = 1;
        ht->ht_next = NULL;
        ht->ht_prev = NULL;

        /*
         * Zero out any freshly allocated page table
         */
        if (need_to_zero)
                x86pte_zero(ht, 0, mmu.ptes_per_table);

#if defined(__amd64) && defined(__xpv)
        if (!is_bare && kpm_vbase) {
                (void) xen_kpm_page(ht->ht_pfn, PT_VALID);
                if (level == mmu.max_level)
                        (void) xen_kpm_page(hat->hat_user_ptable, PT_VALID);
        }
#endif

        return (ht);
}

/*
 * Free up an htable, either to a hat's cached list, the reserves or
 * back to kmem.
 */
static void
htable_free(htable_t *ht)
{
        hat_t *hat = ht->ht_hat;

        /*
         * If the process isn't exiting, cache the free htable in the hat
         * structure. We always do this for the boot time reserve. We don't
         * do this if the hat is exiting or we are stealing/reaping htables.
         */
        if (hat != NULL &&
            !(ht->ht_flags & HTABLE_SHARED_PFN) &&
            (use_boot_reserve ||
            (!(hat->hat_flags & HAT_FREEING) && !htable_dont_cache))) {
                ASSERT((ht->ht_flags & HTABLE_VLP) == 0);
                ASSERT(ht->ht_pfn != PFN_INVALID);
                hat_enter(hat);
                ht->ht_next = hat->hat_ht_cached;
                hat->hat_ht_cached = ht;
                hat_exit(hat);
                return;
        }

        /*
         * If we have a hardware page table, free it.
         * We don't free page tables that are accessed by sharing.
         */
        if (ht->ht_flags & HTABLE_SHARED_PFN) {
                ASSERT(ht->ht_pfn != PFN_INVALID);
        } else if (!(ht->ht_flags & HTABLE_VLP)) {
                ptable_free(ht->ht_pfn);
#if defined(__amd64) && defined(__xpv)
                if (ht->ht_level == mmu.max_level) {
                        ptable_free(hat->hat_user_ptable);
                        hat->hat_user_ptable = PFN_INVALID;
                }
#endif
        }
        ht->ht_pfn = PFN_INVALID;

        /*
         * Free it or put into reserves.
         */
        if (USE_HAT_RESERVES() || htable_reserve_cnt < htable_reserve_amount) {
                htable_put_reserve(ht);
        } else {
                kmem_cache_free(htable_cache, ht);
                htable_adjust_reserve();
        }
}


/*
 * This is called when a hat is being destroyed or swapped out. We reap all
 * the remaining htables in the hat cache. If destroying all left over
 * htables are also destroyed.
 *
 * We also don't need to invalidate any of the PTPs nor do any demapping.
 */
void
htable_purge_hat(hat_t *hat)
{
        htable_t *ht;
        int h;

        /*
         * Purge the htable cache if just reaping.
         */
        if (!(hat->hat_flags & HAT_FREEING)) {
                atomic_inc_32(&htable_dont_cache);
                for (;;) {
                        hat_enter(hat);
                        ht = hat->hat_ht_cached;
                        if (ht == NULL) {
                                hat_exit(hat);
                                break;
                        }
                        hat->hat_ht_cached = ht->ht_next;
                        hat_exit(hat);
                        htable_free(ht);
                }
                atomic_dec_32(&htable_dont_cache);
                return;
        }

        /*
         * if freeing, no locking is needed
         */
        while ((ht = hat->hat_ht_cached) != NULL) {
                hat->hat_ht_cached = ht->ht_next;
                htable_free(ht);
        }

        /*
         * walk thru the htable hash table and free all the htables in it.
         */
        for (h = 0; h < hat->hat_num_hash; ++h) {
                while ((ht = hat->hat_ht_hash[h]) != NULL) {
                        if (ht->ht_next)
                                ht->ht_next->ht_prev = ht->ht_prev;

                        if (ht->ht_prev) {
                                ht->ht_prev->ht_next = ht->ht_next;
                        } else {
                                ASSERT(hat->hat_ht_hash[h] == ht);
                                hat->hat_ht_hash[h] = ht->ht_next;
                        }
                        htable_free(ht);
                }
        }
}

/*
 * Unlink an entry for a table at vaddr and level out of the existing table
 * one level higher. We are always holding the HASH_ENTER() when doing this.
 */
static void
unlink_ptp(htable_t *higher, htable_t *old, uintptr_t vaddr)
{
        uint_t          entry = htable_va2entry(vaddr, higher);
        x86pte_t        expect = MAKEPTP(old->ht_pfn, old->ht_level);
        x86pte_t        found;
        hat_t           *hat = old->ht_hat;

        ASSERT(higher->ht_busy > 0);
        ASSERT(higher->ht_valid_cnt > 0);
        ASSERT(old->ht_valid_cnt == 0);
        found = x86pte_cas(higher, entry, expect, 0);
#ifdef __xpv
        /*
         * This is weird, but Xen apparently automatically unlinks empty
         * pagetables from the upper page table. So allow PTP to be 0 already.
         */
        if (found != expect && found != 0)
#else
        if (found != expect)
#endif
                panic("Bad PTP found=" FMT_PTE ", expected=" FMT_PTE,
                    found, expect);

        /*
         * When a top level VLP page table entry changes, we must issue
         * a reload of cr3 on all processors.
         *
         * If we don't need do do that, then we still have to INVLPG against
         * an address covered by the inner page table, as the latest processors
         * have TLB-like caches for non-leaf page table entries.
         */
        if (!(hat->hat_flags & HAT_FREEING)) {
                hat_tlb_inval(hat, (higher->ht_flags & HTABLE_VLP) ?
                    DEMAP_ALL_ADDR : old->ht_vaddr);
        }

        HTABLE_DEC(higher->ht_valid_cnt);
}

/*
 * Link an entry for a new table at vaddr and level into the existing table
 * one level higher. We are always holding the HASH_ENTER() when doing this.
 */
static void
link_ptp(htable_t *higher, htable_t *new, uintptr_t vaddr)
{
        uint_t          entry = htable_va2entry(vaddr, higher);
        x86pte_t        newptp = MAKEPTP(new->ht_pfn, new->ht_level);
        x86pte_t        found;

        ASSERT(higher->ht_busy > 0);

        ASSERT(new->ht_level != mmu.max_level);

        HTABLE_INC(higher->ht_valid_cnt);

        found = x86pte_cas(higher, entry, 0, newptp);
        if ((found & ~PT_REF) != 0)
                panic("HAT: ptp not 0, found=" FMT_PTE, found);

        /*
         * When any top level VLP page table entry changes, we must issue
         * a reload of cr3 on all processors using it.
         * We also need to do this for the kernel hat on PAE 32 bit kernel.
         */
        if (
#ifdef __i386
            (higher->ht_hat == kas.a_hat && higher->ht_level == VLP_LEVEL) ||
#endif
            (higher->ht_flags & HTABLE_VLP))
                hat_tlb_inval(higher->ht_hat, DEMAP_ALL_ADDR);
}

/*
 * Release of hold on an htable. If this is the last use and the pagetable
 * is empty we may want to free it, then recursively look at the pagetable
 * above it. The recursion is handled by the outer while() loop.
 *
 * On the metal, during process exit, we don't bother unlinking the tables from
 * upper level pagetables. They are instead handled in bulk by hat_free_end().
 * We can't do this on the hypervisor as we need the page table to be
 * implicitly unpinnned before it goes to the free page lists. This can't
 * happen unless we fully unlink it from the page table hierarchy.
 */
void
htable_release(htable_t *ht)
{
        uint_t          hashval;
        htable_t        *shared;
        htable_t        *higher;
        hat_t           *hat;
        uintptr_t       va;
        level_t         level;

        while (ht != NULL) {
                shared = NULL;
                for (;;) {
                        hat = ht->ht_hat;
                        va = ht->ht_vaddr;
                        level = ht->ht_level;
                        hashval = HTABLE_HASH(hat, va, level);

                        /*
                         * The common case is that this isn't the last use of
                         * an htable so we don't want to free the htable.
                         */
                        HTABLE_ENTER(hashval);
                        ASSERT(ht->ht_valid_cnt >= 0);
                        ASSERT(ht->ht_busy > 0);
                        if (ht->ht_valid_cnt > 0)
                                break;
                        if (ht->ht_busy > 1)
                                break;
                        ASSERT(ht->ht_lock_cnt == 0);

#if !defined(__xpv)
                        /*
                         * we always release empty shared htables
                         */
                        if (!(ht->ht_flags & HTABLE_SHARED_PFN)) {

                                /*
                                 * don't release if in address space tear down
                                 */
                                if (hat->hat_flags & HAT_FREEING)
                                        break;

                                /*
                                 * At and above max_page_level, free if it's for
                                 * a boot-time kernel mapping below kernelbase.
                                 */
                                if (level >= mmu.max_page_level &&
                                    (hat != kas.a_hat || va >= kernelbase))
                                        break;
                        }
#endif /* __xpv */

                        /*
                         * Remember if we destroy an htable that shares its PFN
                         * from elsewhere.
                         */
                        if (ht->ht_flags & HTABLE_SHARED_PFN) {
                                ASSERT(shared == NULL);
                                shared = ht->ht_shares;
                                HATSTAT_INC(hs_htable_unshared);
                        }

                        /*
                         * Handle release of a table and freeing the htable_t.
                         * Unlink it from the table higher (ie. ht_parent).
                         */
                        higher = ht->ht_parent;
                        ASSERT(higher != NULL);

                        /*
                         * Unlink the pagetable.
                         */
                        unlink_ptp(higher, ht, va);

                        /*
                         * remove this htable from its hash list
                         */
                        if (ht->ht_next)
                                ht->ht_next->ht_prev = ht->ht_prev;

                        if (ht->ht_prev) {
                                ht->ht_prev->ht_next = ht->ht_next;
                        } else {
                                ASSERT(hat->hat_ht_hash[hashval] == ht);
                                hat->hat_ht_hash[hashval] = ht->ht_next;
                        }
                        HTABLE_EXIT(hashval);
                        htable_free(ht);
                        ht = higher;
                }

                ASSERT(ht->ht_busy >= 1);
                --ht->ht_busy;
                HTABLE_EXIT(hashval);

                /*
                 * If we released a shared htable, do a release on the htable
                 * from which it shared
                 */
                ht = shared;
        }
}

/*
 * Find the htable for the pagetable at the given level for the given address.
 * If found acquires a hold that eventually needs to be htable_release()d
 */
htable_t *
htable_lookup(hat_t *hat, uintptr_t vaddr, level_t level)
{
        uintptr_t       base;
        uint_t          hashval;
        htable_t        *ht = NULL;

        ASSERT(level >= 0);
        ASSERT(level <= TOP_LEVEL(hat));

        if (level == TOP_LEVEL(hat)) {
#if defined(__amd64)
                /*
                 * 32 bit address spaces on 64 bit kernels need to check
                 * for overflow of the 32 bit address space
                 */
                if ((hat->hat_flags & HAT_VLP) && vaddr >= ((uint64_t)1 << 32))
                        return (NULL);
#endif
                base = 0;
        } else {
                base = vaddr & LEVEL_MASK(level + 1);
        }

        hashval = HTABLE_HASH(hat, base, level);
        HTABLE_ENTER(hashval);
        for (ht = hat->hat_ht_hash[hashval]; ht; ht = ht->ht_next) {
                if (ht->ht_hat == hat &&
                    ht->ht_vaddr == base &&
                    ht->ht_level == level)
                        break;
        }
        if (ht)
                ++ht->ht_busy;

        HTABLE_EXIT(hashval);
        return (ht);
}

/*
 * Acquires a hold on a known htable (from a locked hment entry).
 */
void
htable_acquire(htable_t *ht)
{
        hat_t           *hat = ht->ht_hat;
        level_t         level = ht->ht_level;
        uintptr_t       base = ht->ht_vaddr;
        uint_t          hashval = HTABLE_HASH(hat, base, level);

        HTABLE_ENTER(hashval);
#ifdef DEBUG
        /*
         * make sure the htable is there
         */
        {
                htable_t        *h;

                for (h = hat->hat_ht_hash[hashval];
                    h && h != ht;
                    h = h->ht_next)
                        ;
                ASSERT(h == ht);
        }
#endif /* DEBUG */
        ++ht->ht_busy;
        HTABLE_EXIT(hashval);
}

/*
 * Find the htable for the pagetable at the given level for the given address.
 * If found acquires a hold that eventually needs to be htable_release()d
 * If not found the table is created.
 *
 * Since we can't hold a hash table mutex during allocation, we have to
 * drop it and redo the search on a create. Then we may have to free the newly
 * allocated htable if another thread raced in and created it ahead of us.
 */
htable_t *
htable_create(
        hat_t           *hat,
        uintptr_t       vaddr,
        level_t         level,
        htable_t        *shared)
{
        uint_t          h;
        level_t         l;
        uintptr_t       base;
        htable_t        *ht;
        htable_t        *higher = NULL;
        htable_t        *new = NULL;

        if (level < 0 || level > TOP_LEVEL(hat))
                panic("htable_create(): level %d out of range\n", level);

        /*
         * Create the page tables in top down order.
         */
        for (l = TOP_LEVEL(hat); l >= level; --l) {
                new = NULL;
                if (l == TOP_LEVEL(hat))
                        base = 0;
                else
                        base = vaddr & LEVEL_MASK(l + 1);

                h = HTABLE_HASH(hat, base, l);
try_again:
                /*
                 * look up the htable at this level
                 */
                HTABLE_ENTER(h);
                if (l == TOP_LEVEL(hat)) {
                        ht = hat->hat_htable;
                } else {
                        for (ht = hat->hat_ht_hash[h]; ht; ht = ht->ht_next) {
                                ASSERT(ht->ht_hat == hat);
                                if (ht->ht_vaddr == base &&
                                    ht->ht_level == l)
                                        break;
                        }
                }

                /*
                 * if we found the htable, increment its busy cnt
                 * and if we had allocated a new htable, free it.
                 */
                if (ht != NULL) {
                        /*
                         * If we find a pre-existing shared table, it must
                         * share from the same place.
                         */
                        if (l == level && shared && ht->ht_shares &&
                            ht->ht_shares != shared) {
                                panic("htable shared from wrong place "
                                    "found htable=%p shared=%p",
                                    (void *)ht, (void *)shared);
                        }
                        ++ht->ht_busy;
                        HTABLE_EXIT(h);
                        if (new)
                                htable_free(new);
                        if (higher != NULL)
                                htable_release(higher);
                        higher = ht;

                /*
                 * if we didn't find it on the first search
                 * allocate a new one and search again
                 */
                } else if (new == NULL) {
                        HTABLE_EXIT(h);
                        new = htable_alloc(hat, base, l,
                            l == level ? shared : NULL);
                        goto try_again;

                /*
                 * 2nd search and still not there, use "new" table
                 * Link new table into higher, when not at top level.
                 */
                } else {
                        ht = new;
                        if (higher != NULL) {
                                link_ptp(higher, ht, base);
                                ht->ht_parent = higher;
                        }
                        ht->ht_next = hat->hat_ht_hash[h];
                        ASSERT(ht->ht_prev == NULL);
                        if (hat->hat_ht_hash[h])
                                hat->hat_ht_hash[h]->ht_prev = ht;
                        hat->hat_ht_hash[h] = ht;
                        HTABLE_EXIT(h);

                        /*
                         * Note we don't do htable_release(higher).
                         * That happens recursively when "new" is removed by
                         * htable_release() or htable_steal().
                         */
                        higher = ht;

                        /*
                         * If we just created a new shared page table we
                         * increment the shared htable's busy count, so that
                         * it can't be the victim of a steal even if it's empty.
                         */
                        if (l == level && shared) {
                                (void) htable_lookup(shared->ht_hat,
                                    shared->ht_vaddr, shared->ht_level);
                                HATSTAT_INC(hs_htable_shared);
                        }
                }
        }

        return (ht);
}

/*
 * Inherit initial pagetables from the boot program. On the 64-bit
 * hypervisor we also temporarily mark the p_index field of page table
 * pages, so we know not to try making them writable in seg_kpm.
 */
void
htable_attach(
        hat_t *hat,
        uintptr_t base,
        level_t level,
        htable_t *parent,
        pfn_t pfn)
{
        htable_t        *ht;
        uint_t          h;
        uint_t          i;
        x86pte_t        pte;
        x86pte_t        *ptep;
        page_t          *pp;
        extern page_t   *boot_claim_page(pfn_t);

        ht = htable_get_reserve();
        if (level == mmu.max_level)
                kas.a_hat->hat_htable = ht;
        ht->ht_hat = hat;
        ht->ht_parent = parent;
        ht->ht_vaddr = base;
        ht->ht_level = level;
        ht->ht_busy = 1;
        ht->ht_next = NULL;
        ht->ht_prev = NULL;
        ht->ht_flags = 0;
        ht->ht_pfn = pfn;
        ht->ht_lock_cnt = 0;
        ht->ht_valid_cnt = 0;
        if (parent != NULL)
                ++parent->ht_busy;

        h = HTABLE_HASH(hat, base, level);
        HTABLE_ENTER(h);
        ht->ht_next = hat->hat_ht_hash[h];
        ASSERT(ht->ht_prev == NULL);
        if (hat->hat_ht_hash[h])
                hat->hat_ht_hash[h]->ht_prev = ht;
        hat->hat_ht_hash[h] = ht;
        HTABLE_EXIT(h);

        /*
         * make sure the page table physical page is not FREE
         */
        if (page_resv(1, KM_NOSLEEP) == 0)
                panic("page_resv() failed in ptable alloc");

        pp = boot_claim_page(pfn);
        ASSERT(pp != NULL);

        /*
         * Page table pages that were allocated by dboot or
         * in very early startup didn't go through boot_mapin()
         * and so won't have vnode/offsets. Fix that here.
         */
        if (pp->p_vnode == NULL) {
                /* match offset calculation in page_get_physical() */
                u_offset_t offset = (uintptr_t)ht;
                if (offset > kernelbase)
                        offset -= kernelbase;
                offset <<= MMU_PAGESHIFT;
#if defined(__amd64)
                offset += mmu.hole_start;       /* something in VA hole */
#else
                offset += 1ULL << 40;           /* something > 4 Gig */
#endif
                ASSERT(page_exists(&kvp, offset) == NULL);
                (void) page_hashin(pp, &kvp, offset, NULL);
        }
        page_downgrade(pp);
#if defined(__xpv) && defined(__amd64)
        /*
         * Record in the page_t that is a pagetable for segkpm setup.
         */
        if (kpm_vbase)
                pp->p_index = 1;
#endif

        /*
         * Count valid mappings and recursively attach lower level pagetables.
         */
        ptep = kbm_remap_window(pfn_to_pa(pfn), 0);
        for (i = 0; i < HTABLE_NUM_PTES(ht); ++i) {
                if (mmu.pae_hat)
                        pte = ptep[i];
                else
                        pte = ((x86pte32_t *)ptep)[i];
                if (!IN_HYPERVISOR_VA(base) && PTE_ISVALID(pte)) {
                        ++ht->ht_valid_cnt;
                        if (!PTE_ISPAGE(pte, level)) {
                                htable_attach(hat, base, level - 1,
                                    ht, PTE2PFN(pte, level));
                                ptep = kbm_remap_window(pfn_to_pa(pfn), 0);
                        }
                }
                base += LEVEL_SIZE(level);
                if (base == mmu.hole_start)
                        base = (mmu.hole_end + MMU_PAGEOFFSET) & MMU_PAGEMASK;
        }

        /*
         * As long as all the mappings we had were below kernel base
         * we can release the htable.
         */
        if (base < kernelbase)
                htable_release(ht);
}

/*
 * Walk through a given htable looking for the first valid entry.  This
 * routine takes both a starting and ending address.  The starting address
 * is required to be within the htable provided by the caller, but there is
 * no such restriction on the ending address.
 *
 * If the routine finds a valid entry in the htable (at or beyond the
 * starting address), the PTE (and its address) will be returned.
 * This PTE may correspond to either a page or a pagetable - it is the
 * caller's responsibility to determine which.  If no valid entry is
 * found, 0 (and invalid PTE) and the next unexamined address will be
 * returned.
 *
 * The loop has been carefully coded for optimization.
 */
static x86pte_t
htable_scan(htable_t *ht, uintptr_t *vap, uintptr_t eaddr)
{
        uint_t e;
        x86pte_t found_pte = (x86pte_t)0;
        caddr_t pte_ptr;
        caddr_t end_pte_ptr;
        int l = ht->ht_level;
        uintptr_t va = *vap & LEVEL_MASK(l);
        size_t pgsize = LEVEL_SIZE(l);

        ASSERT(va >= ht->ht_vaddr);
        ASSERT(va <= HTABLE_LAST_PAGE(ht));

        /*
         * Compute the starting index and ending virtual address
         */
        e = htable_va2entry(va, ht);

        /*
         * The following page table scan code knows that the valid
         * bit of a PTE is in the lowest byte AND that x86 is little endian!!
         */
        pte_ptr = (caddr_t)x86pte_access_pagetable(ht, 0);
        end_pte_ptr = (caddr_t)PT_INDEX_PTR(pte_ptr, HTABLE_NUM_PTES(ht));
        pte_ptr = (caddr_t)PT_INDEX_PTR((x86pte_t *)pte_ptr, e);
        while (!PTE_ISVALID(*pte_ptr)) {
                va += pgsize;
                if (va >= eaddr)
                        break;
                pte_ptr += mmu.pte_size;
                ASSERT(pte_ptr <= end_pte_ptr);
                if (pte_ptr == end_pte_ptr)
                        break;
        }

        /*
         * if we found a valid PTE, load the entire PTE
         */
        if (va < eaddr && pte_ptr != end_pte_ptr)
                found_pte = GET_PTE((x86pte_t *)pte_ptr);
        x86pte_release_pagetable(ht);

#if defined(__amd64)
        /*
         * deal with VA hole on amd64
         */
        if (l == mmu.max_level && va >= mmu.hole_start && va <= mmu.hole_end)
                va = mmu.hole_end + va - mmu.hole_start;
#endif /* __amd64 */

        *vap = va;
        return (found_pte);
}

/*
 * Find the address and htable for the first populated translation at or
 * above the given virtual address.  The caller may also specify an upper
 * limit to the address range to search.  Uses level information to quickly
 * skip unpopulated sections of virtual address spaces.
 *
 * If not found returns NULL. When found, returns the htable and virt addr
 * and has a hold on the htable.
 */
x86pte_t
htable_walk(
        struct hat *hat,
        htable_t **htp,
        uintptr_t *vaddr,
        uintptr_t eaddr)
{
        uintptr_t va = *vaddr;
        htable_t *ht;
        htable_t *prev = *htp;
        level_t l;
        level_t max_mapped_level;
        x86pte_t pte;

        ASSERT(eaddr > va);

        /*
         * If this is a user address, then we know we need not look beyond
         * kernelbase.
         */
        ASSERT(hat == kas.a_hat || eaddr <= kernelbase ||
            eaddr == HTABLE_WALK_TO_END);
        if (hat != kas.a_hat && eaddr == HTABLE_WALK_TO_END)
                eaddr = kernelbase;

        /*
         * If we're coming in with a previous page table, search it first
         * without doing an htable_lookup(), this should be frequent.
         */
        if (prev) {
                ASSERT(prev->ht_busy > 0);
                ASSERT(prev->ht_vaddr <= va);
                l = prev->ht_level;
                if (va <= HTABLE_LAST_PAGE(prev)) {
                        pte = htable_scan(prev, &va, eaddr);

                        if (PTE_ISPAGE(pte, l)) {
                                *vaddr = va;
                                *htp = prev;
                                return (pte);
                        }
                }

                /*
                 * We found nothing in the htable provided by the caller,
                 * so fall through and do the full search
                 */
                htable_release(prev);
        }

        /*
         * Find the level of the largest pagesize used by this HAT.
         */
        if (hat->hat_ism_pgcnt > 0) {
                max_mapped_level = mmu.umax_page_level;
        } else {
                max_mapped_level = 0;
                for (l = 1; l <= mmu.max_page_level; ++l)
                        if (hat->hat_pages_mapped[l] != 0)
                                max_mapped_level = l;
        }

        while (va < eaddr && va >= *vaddr) {
                ASSERT(!IN_VA_HOLE(va));

                /*
                 *  Find lowest table with any entry for given address.
                 */
                for (l = 0; l <= TOP_LEVEL(hat); ++l) {
                        ht = htable_lookup(hat, va, l);
                        if (ht != NULL) {
                                pte = htable_scan(ht, &va, eaddr);
                                if (PTE_ISPAGE(pte, l)) {
                                        *vaddr = va;
                                        *htp = ht;
                                        return (pte);
                                }
                                htable_release(ht);
                                break;
                        }

                        /*
                         * No htable at this level for the address. If there
                         * is no larger page size that could cover it, we can
                         * skip right to the start of the next page table.
                         */
                        ASSERT(l < TOP_LEVEL(hat));
                        if (l >= max_mapped_level) {
                                va = NEXT_ENTRY_VA(va, l + 1);
                                if (va >= eaddr)
                                        break;
                        }
                }
        }

        *vaddr = 0;
        *htp = NULL;
        return (0);
}

/*
 * Find the htable and page table entry index of the given virtual address
 * with pagesize at or below given level.
 * If not found returns NULL. When found, returns the htable, sets
 * entry, and has a hold on the htable.
 */
htable_t *
htable_getpte(
        struct hat *hat,
        uintptr_t vaddr,
        uint_t *entry,
        x86pte_t *pte,
        level_t level)
{
        htable_t        *ht;
        level_t         l;
        uint_t          e;

        ASSERT(level <= mmu.max_page_level);

        for (l = 0; l <= level; ++l) {
                ht = htable_lookup(hat, vaddr, l);
                if (ht == NULL)
                        continue;
                e = htable_va2entry(vaddr, ht);
                if (entry != NULL)
                        *entry = e;
                if (pte != NULL)
                        *pte = x86pte_get(ht, e);
                return (ht);
        }
        return (NULL);
}

/*
 * Find the htable and page table entry index of the given virtual address.
 * There must be a valid page mapped at the given address.
 * If not found returns NULL. When found, returns the htable, sets
 * entry, and has a hold on the htable.
 */
htable_t *
htable_getpage(struct hat *hat, uintptr_t vaddr, uint_t *entry)
{
        htable_t        *ht;
        uint_t          e;
        x86pte_t        pte;

        ht = htable_getpte(hat, vaddr, &e, &pte, mmu.max_page_level);
        if (ht == NULL)
                return (NULL);

        if (entry)
                *entry = e;

        if (PTE_ISPAGE(pte, ht->ht_level))
                return (ht);
        htable_release(ht);
        return (NULL);
}


void
htable_init()
{
        /*
         * To save on kernel VA usage, we avoid debug information in 32 bit
         * kernels.
         */
#if defined(__amd64)
        int     kmem_flags = KMC_NOHASH;
#elif defined(__i386)
        int     kmem_flags = KMC_NOHASH | KMC_NODEBUG;
#endif

        /*
         * initialize kmem caches
         */
        htable_cache = kmem_cache_create("htable_t",
            sizeof (htable_t), 0, NULL, NULL,
            htable_reap, NULL, hat_memload_arena, kmem_flags);
}

/*
 * get the pte index for the virtual address in the given htable's pagetable
 */
uint_t
htable_va2entry(uintptr_t va, htable_t *ht)
{
        level_t l = ht->ht_level;

        ASSERT(va >= ht->ht_vaddr);
        ASSERT(va <= HTABLE_LAST_PAGE(ht));
        return ((va >> LEVEL_SHIFT(l)) & (HTABLE_NUM_PTES(ht) - 1));
}

/*
 * Given an htable and the index of a pte in it, return the virtual address
 * of the page.
 */
uintptr_t
htable_e2va(htable_t *ht, uint_t entry)
{
        level_t l = ht->ht_level;
        uintptr_t va;

        ASSERT(entry < HTABLE_NUM_PTES(ht));
        va = ht->ht_vaddr + ((uintptr_t)entry << LEVEL_SHIFT(l));

        /*
         * Need to skip over any VA hole in top level table
         */
#if defined(__amd64)
        if (ht->ht_level == mmu.max_level && va >= mmu.hole_start)
                va += ((mmu.hole_end - mmu.hole_start) + 1);
#endif

        return (va);
}

/*
 * The code uses compare and swap instructions to read/write PTE's to
 * avoid atomicity problems, since PTEs can be 8 bytes on 32 bit systems.
 * will naturally be atomic.
 *
 * The combination of using kpreempt_disable()/_enable() and the hci_mutex
 * are used to ensure that an interrupt won't overwrite a temporary mapping
 * while it's in use. If an interrupt thread tries to access a PTE, it will
 * yield briefly back to the pinned thread which holds the cpu's hci_mutex.
 */
void
x86pte_cpu_init(cpu_t *cpu)
{
        struct hat_cpu_info *hci;

        hci = kmem_zalloc(sizeof (*hci), KM_SLEEP);
        mutex_init(&hci->hci_mutex, NULL, MUTEX_DEFAULT, NULL);
        cpu->cpu_hat_info = hci;
}

void
x86pte_cpu_fini(cpu_t *cpu)
{
        struct hat_cpu_info *hci = cpu->cpu_hat_info;

        kmem_free(hci, sizeof (*hci));
        cpu->cpu_hat_info = NULL;
}

#ifdef __i386
/*
 * On 32 bit kernels, loading a 64 bit PTE is a little tricky
 */
x86pte_t
get_pte64(x86pte_t *ptr)
{
        volatile uint32_t *p = (uint32_t *)ptr;
        x86pte_t t;

        ASSERT(mmu.pae_hat != 0);
        for (;;) {
                t = p[0];
                t |= (uint64_t)p[1] << 32;
                if ((t & 0xffffffff) == p[0])
                        return (t);
        }
}
#endif /* __i386 */

/*
 * Disable preemption and establish a mapping to the pagetable with the
 * given pfn. This is optimized for there case where it's the same
 * pfn as we last used referenced from this CPU.
 */
static x86pte_t *
x86pte_access_pagetable(htable_t *ht, uint_t index)
{
        /*
         * VLP pagetables are contained in the hat_t
         */
        if (ht->ht_flags & HTABLE_VLP)
                return (PT_INDEX_PTR(ht->ht_hat->hat_vlp_ptes, index));
        return (x86pte_mapin(ht->ht_pfn, index, ht));
}

/*
 * map the given pfn into the page table window.
 */
/*ARGSUSED*/
x86pte_t *
x86pte_mapin(pfn_t pfn, uint_t index, htable_t *ht)
{
        x86pte_t *pteptr;
        x86pte_t pte = 0;
        x86pte_t newpte;
        int x;

        ASSERT(pfn != PFN_INVALID);

        if (!khat_running) {
                caddr_t va = kbm_remap_window(pfn_to_pa(pfn), 1);
                return (PT_INDEX_PTR(va, index));
        }

        /*
         * If kpm is available, use it.
         */
        if (kpm_vbase)
                return (PT_INDEX_PTR(hat_kpm_pfn2va(pfn), index));

        /*
         * Disable preemption and grab the CPU's hci_mutex
         */
        kpreempt_disable();
        ASSERT(CPU->cpu_hat_info != NULL);
        mutex_enter(&CPU->cpu_hat_info->hci_mutex);
        x = PWIN_TABLE(CPU->cpu_id);
        pteptr = (x86pte_t *)PWIN_PTE_VA(x);
#ifndef __xpv
        if (mmu.pae_hat)
                pte = *pteptr;
        else
                pte = *(x86pte32_t *)pteptr;
#endif

        newpte = MAKEPTE(pfn, 0) | mmu.pt_global | mmu.pt_nx;

        /*
         * For hardware we can use a writable mapping.
         */
#ifdef __xpv
        if (IN_XPV_PANIC())
#endif
                newpte |= PT_WRITABLE;

        if (!PTE_EQUIV(newpte, pte)) {

#ifdef __xpv
                if (!IN_XPV_PANIC()) {
                        xen_map(newpte, PWIN_VA(x));
                } else
#endif
                {
                        XPV_ALLOW_PAGETABLE_UPDATES();
                        if (mmu.pae_hat)
                                *pteptr = newpte;
                        else
                                *(x86pte32_t *)pteptr = newpte;
                        XPV_DISALLOW_PAGETABLE_UPDATES();
                        mmu_tlbflush_entry((caddr_t)(PWIN_VA(x)));
                }
        }
        return (PT_INDEX_PTR(PWIN_VA(x), index));
}

/*
 * Release access to a page table.
 */
static void
x86pte_release_pagetable(htable_t *ht)
{
        /*
         * nothing to do for VLP htables
         */
        if (ht->ht_flags & HTABLE_VLP)
                return;

        x86pte_mapout();
}

void
x86pte_mapout(void)
{
        if (kpm_vbase != NULL || !khat_running)
                return;

        /*
         * Drop the CPU's hci_mutex and restore preemption.
         */
#ifdef __xpv
        if (!IN_XPV_PANIC()) {
                uintptr_t va;

                /*
                 * We need to always clear the mapping in case a page
                 * that was once a page table page is ballooned out.
                 */
                va = (uintptr_t)PWIN_VA(PWIN_TABLE(CPU->cpu_id));
                (void) HYPERVISOR_update_va_mapping(va, 0,
                    UVMF_INVLPG | UVMF_LOCAL);
        }
#endif
        mutex_exit(&CPU->cpu_hat_info->hci_mutex);
        kpreempt_enable();
}

/*
 * Atomic retrieval of a pagetable entry
 */
x86pte_t
x86pte_get(htable_t *ht, uint_t entry)
{
        x86pte_t        pte;
        x86pte_t        *ptep;

        /*
         * Be careful that loading PAE entries in 32 bit kernel is atomic.
         */
        ASSERT(entry < mmu.ptes_per_table);
        ptep = x86pte_access_pagetable(ht, entry);
        pte = GET_PTE(ptep);
        x86pte_release_pagetable(ht);
        return (pte);
}

/*
 * Atomic unconditional set of a page table entry, it returns the previous
 * value. For pre-existing mappings if the PFN changes, then we don't care
 * about the old pte's REF / MOD bits. If the PFN remains the same, we leave
 * the MOD/REF bits unchanged.
 *
 * If asked to overwrite a link to a lower page table with a large page
 * mapping, this routine returns the special value of LPAGE_ERROR. This
 * allows the upper HAT layers to retry with a smaller mapping size.
 */
x86pte_t
x86pte_set(htable_t *ht, uint_t entry, x86pte_t new, void *ptr)
{
        x86pte_t        old;
        x86pte_t        prev;
        x86pte_t        *ptep;
        level_t         l = ht->ht_level;
        x86pte_t        pfn_mask = (l != 0) ? PT_PADDR_LGPG : PT_PADDR;
        x86pte_t        n;
        uintptr_t       addr = htable_e2va(ht, entry);
        hat_t           *hat = ht->ht_hat;

        ASSERT(new != 0); /* don't use to invalidate a PTE, see x86pte_update */
        ASSERT(!(ht->ht_flags & HTABLE_SHARED_PFN));
        if (ptr == NULL)
                ptep = x86pte_access_pagetable(ht, entry);
        else
                ptep = ptr;

        /*
         * Install the new PTE. If remapping the same PFN, then
         * copy existing REF/MOD bits to new mapping.
         */
        do {
                prev = GET_PTE(ptep);
                n = new;
                if (PTE_ISVALID(n) && (prev & pfn_mask) == (new & pfn_mask))
                        n |= prev & (PT_REF | PT_MOD);

                /*
                 * Another thread may have installed this mapping already,
                 * flush the local TLB and be done.
                 */
                if (prev == n) {
                        old = new;
#ifdef __xpv
                        if (!IN_XPV_PANIC())
                                xen_flush_va((caddr_t)addr);
                        else
#endif
                                mmu_tlbflush_entry((caddr_t)addr);
                        goto done;
                }

                /*
                 * Detect if we have a collision of installing a large
                 * page mapping where there already is a lower page table.
                 */
                if (l > 0 && (prev & PT_VALID) && !(prev & PT_PAGESIZE)) {
                        old = LPAGE_ERROR;
                        goto done;
                }

                XPV_ALLOW_PAGETABLE_UPDATES();
                old = CAS_PTE(ptep, prev, n);
                XPV_DISALLOW_PAGETABLE_UPDATES();
        } while (old != prev);

        /*
         * Do a TLB demap if needed, ie. the old pte was valid.
         *
         * Note that a stale TLB writeback to the PTE here either can't happen
         * or doesn't matter. The PFN can only change for NOSYNC|NOCONSIST
         * mappings, but they were created with REF and MOD already set, so
         * no stale writeback will happen.
         *
         * Segmap is the only place where remaps happen on the same pfn and for
         * that we want to preserve the stale REF/MOD bits.
         */
        if (old & PT_REF)
                hat_tlb_inval(hat, addr);

done:
        if (ptr == NULL)
                x86pte_release_pagetable(ht);
        return (old);
}

/*
 * Atomic compare and swap of a page table entry. No TLB invalidates are done.
 * This is used for links between pagetables of different levels.
 * Note we always create these links with dirty/access set, so they should
 * never change.
 */
x86pte_t
x86pte_cas(htable_t *ht, uint_t entry, x86pte_t old, x86pte_t new)
{
        x86pte_t        pte;
        x86pte_t        *ptep;
#ifdef __xpv
        /*
         * We can't use writable pagetables for upper level tables, so fake it.
         */
        mmu_update_t t[2];
        int cnt = 1;
        int count;
        maddr_t ma;

        if (!IN_XPV_PANIC()) {
                ASSERT(!(ht->ht_flags & HTABLE_VLP));   /* no VLP yet */
                ma = pa_to_ma(PT_INDEX_PHYSADDR(pfn_to_pa(ht->ht_pfn), entry));
                t[0].ptr = ma | MMU_NORMAL_PT_UPDATE;
                t[0].val = new;

#if defined(__amd64)
                /*
                 * On the 64-bit hypervisor we need to maintain the user mode
                 * top page table too.
                 */
                if (ht->ht_level == mmu.max_level && ht->ht_hat != kas.a_hat) {
                        ma = pa_to_ma(PT_INDEX_PHYSADDR(pfn_to_pa(
                            ht->ht_hat->hat_user_ptable), entry));
                        t[1].ptr = ma | MMU_NORMAL_PT_UPDATE;
                        t[1].val = new;
                        ++cnt;
                }
#endif  /* __amd64 */

                if (HYPERVISOR_mmu_update(t, cnt, &count, DOMID_SELF))
                        panic("HYPERVISOR_mmu_update() failed");
                ASSERT(count == cnt);
                return (old);
        }
#endif
        ptep = x86pte_access_pagetable(ht, entry);
        XPV_ALLOW_PAGETABLE_UPDATES();
        pte = CAS_PTE(ptep, old, new);
        XPV_DISALLOW_PAGETABLE_UPDATES();
        x86pte_release_pagetable(ht);
        return (pte);
}

/*
 * Invalidate a page table entry as long as it currently maps something that
 * matches the value determined by expect.
 *
 * Also invalidates any TLB entries and returns the previous value of the PTE.
 */
x86pte_t
x86pte_inval(
        htable_t *ht,
        uint_t entry,
        x86pte_t expect,
        x86pte_t *pte_ptr)
{
        x86pte_t        *ptep;
        x86pte_t        oldpte;
        x86pte_t        found;

        ASSERT(!(ht->ht_flags & HTABLE_SHARED_PFN));
        ASSERT(ht->ht_level <= mmu.max_page_level);

        if (pte_ptr != NULL)
                ptep = pte_ptr;
        else
                ptep = x86pte_access_pagetable(ht, entry);

#if defined(__xpv)
        /*
         * If exit()ing just use HYPERVISOR_mmu_update(), as we can't be racing
         * with anything else.
         */
        if ((ht->ht_hat->hat_flags & HAT_FREEING) && !IN_XPV_PANIC()) {
                int count;
                mmu_update_t t[1];
                maddr_t ma;

                oldpte = GET_PTE(ptep);
                if (expect != 0 && (oldpte & PT_PADDR) != (expect & PT_PADDR))
                        goto done;
                ma = pa_to_ma(PT_INDEX_PHYSADDR(pfn_to_pa(ht->ht_pfn), entry));
                t[0].ptr = ma | MMU_NORMAL_PT_UPDATE;
                t[0].val = 0;
                if (HYPERVISOR_mmu_update(t, 1, &count, DOMID_SELF))
                        panic("HYPERVISOR_mmu_update() failed");
                ASSERT(count == 1);
                goto done;
        }
#endif /* __xpv */

        /*
         * Note that the loop is needed to handle changes due to h/w updating
         * of PT_MOD/PT_REF.
         */
        do {
                oldpte = GET_PTE(ptep);
                if (expect != 0 && (oldpte & PT_PADDR) != (expect & PT_PADDR))
                        goto done;
                XPV_ALLOW_PAGETABLE_UPDATES();
                found = CAS_PTE(ptep, oldpte, 0);
                XPV_DISALLOW_PAGETABLE_UPDATES();
        } while (found != oldpte);
        if (oldpte & (PT_REF | PT_MOD))
                hat_tlb_inval(ht->ht_hat, htable_e2va(ht, entry));

done:
        if (pte_ptr == NULL)
                x86pte_release_pagetable(ht);
        return (oldpte);
}

/*
 * Change a page table entry af it currently matches the value in expect.
 */
x86pte_t
x86pte_update(
        htable_t *ht,
        uint_t entry,
        x86pte_t expect,
        x86pte_t new)
{
        x86pte_t        *ptep;
        x86pte_t        found;

        ASSERT(new != 0);
        ASSERT(!(ht->ht_flags & HTABLE_SHARED_PFN));
        ASSERT(ht->ht_level <= mmu.max_page_level);

        ptep = x86pte_access_pagetable(ht, entry);
        XPV_ALLOW_PAGETABLE_UPDATES();
        found = CAS_PTE(ptep, expect, new);
        XPV_DISALLOW_PAGETABLE_UPDATES();
        if (found == expect) {
                hat_tlb_inval(ht->ht_hat, htable_e2va(ht, entry));

                /*
                 * When removing write permission *and* clearing the
                 * MOD bit, check if a write happened via a stale
                 * TLB entry before the TLB shootdown finished.
                 *
                 * If it did happen, simply re-enable write permission and
                 * act like the original CAS failed.
                 */
                if ((expect & (PT_WRITABLE | PT_MOD)) == PT_WRITABLE &&
                    (new & (PT_WRITABLE | PT_MOD)) == 0 &&
                    (GET_PTE(ptep) & PT_MOD) != 0) {
                        do {
                                found = GET_PTE(ptep);
                                XPV_ALLOW_PAGETABLE_UPDATES();
                                found =
                                    CAS_PTE(ptep, found, found | PT_WRITABLE);
                                XPV_DISALLOW_PAGETABLE_UPDATES();
                        } while ((found & PT_WRITABLE) == 0);
                }
        }
        x86pte_release_pagetable(ht);
        return (found);
}

#ifndef __xpv
/*
 * Copy page tables - this is just a little more complicated than the
 * previous routines. Note that it's also not atomic! It also is never
 * used for VLP pagetables.
 */
void
x86pte_copy(htable_t *src, htable_t *dest, uint_t entry, uint_t count)
{
        caddr_t src_va;
        caddr_t dst_va;
        size_t size;
        x86pte_t *pteptr;
        x86pte_t pte;

        ASSERT(khat_running);
        ASSERT(!(dest->ht_flags & HTABLE_VLP));
        ASSERT(!(src->ht_flags & HTABLE_VLP));
        ASSERT(!(src->ht_flags & HTABLE_SHARED_PFN));
        ASSERT(!(dest->ht_flags & HTABLE_SHARED_PFN));

        /*
         * Acquire access to the CPU pagetable windows for the dest and source.
         */
        dst_va = (caddr_t)x86pte_access_pagetable(dest, entry);
        if (kpm_vbase) {
                src_va = (caddr_t)
                    PT_INDEX_PTR(hat_kpm_pfn2va(src->ht_pfn), entry);
        } else {
                uint_t x = PWIN_SRC(CPU->cpu_id);

                /*
                 * Finish defining the src pagetable mapping
                 */
                src_va = (caddr_t)PT_INDEX_PTR(PWIN_VA(x), entry);
                pte = MAKEPTE(src->ht_pfn, 0) | mmu.pt_global | mmu.pt_nx;
                pteptr = (x86pte_t *)PWIN_PTE_VA(x);
                if (mmu.pae_hat)
                        *pteptr = pte;
                else
                        *(x86pte32_t *)pteptr = pte;
                mmu_tlbflush_entry((caddr_t)(PWIN_VA(x)));
        }

        /*
         * now do the copy
         */
        size = count << mmu.pte_size_shift;
        bcopy(src_va, dst_va, size);

        x86pte_release_pagetable(dest);
}

#else /* __xpv */

/*
 * The hypervisor only supports writable pagetables at level 0, so we have
 * to install these 1 by 1 the slow way.
 */
void
x86pte_copy(htable_t *src, htable_t *dest, uint_t entry, uint_t count)
{
        caddr_t src_va;
        x86pte_t pte;

        ASSERT(!IN_XPV_PANIC());
        src_va = (caddr_t)x86pte_access_pagetable(src, entry);
        while (count) {
                if (mmu.pae_hat)
                        pte = *(x86pte_t *)src_va;
                else
                        pte = *(x86pte32_t *)src_va;
                if (pte != 0) {
                        set_pteval(pfn_to_pa(dest->ht_pfn), entry,
                            dest->ht_level, pte);
#ifdef __amd64
                        if (dest->ht_level == mmu.max_level &&
                            htable_e2va(dest, entry) < HYPERVISOR_VIRT_END)
                                set_pteval(
                                    pfn_to_pa(dest->ht_hat->hat_user_ptable),
                                    entry, dest->ht_level, pte);
#endif
                }
                --count;
                ++entry;
                src_va += mmu.pte_size;
        }
        x86pte_release_pagetable(src);
}
#endif /* __xpv */

/*
 * Zero page table entries - Note this doesn't use atomic stores!
 */
static void
x86pte_zero(htable_t *dest, uint_t entry, uint_t count)
{
        caddr_t dst_va;
        size_t size;
#ifdef __xpv
        int x;
        x86pte_t newpte;
#endif

        /*
         * Map in the page table to be zeroed.
         */
        ASSERT(!(dest->ht_flags & HTABLE_SHARED_PFN));
        ASSERT(!(dest->ht_flags & HTABLE_VLP));

        /*
         * On the hypervisor we don't use x86pte_access_pagetable() since
         * in this case the page is not pinned yet.
         */
#ifdef __xpv
        if (kpm_vbase == NULL) {
                kpreempt_disable();
                ASSERT(CPU->cpu_hat_info != NULL);
                mutex_enter(&CPU->cpu_hat_info->hci_mutex);
                x = PWIN_TABLE(CPU->cpu_id);
                newpte = MAKEPTE(dest->ht_pfn, 0) | PT_WRITABLE;
                xen_map(newpte, PWIN_VA(x));
                dst_va = (caddr_t)PT_INDEX_PTR(PWIN_VA(x), entry);
        } else
#endif
                dst_va = (caddr_t)x86pte_access_pagetable(dest, entry);

        size = count << mmu.pte_size_shift;
        ASSERT(size > BLOCKZEROALIGN);
#ifdef __i386
        if (!is_x86_feature(x86_featureset, X86FSET_SSE2))
                bzero(dst_va, size);
        else
#endif
                block_zero_no_xmm(dst_va, size);

#ifdef __xpv
        if (kpm_vbase == NULL) {
                xen_map(0, PWIN_VA(x));
                mutex_exit(&CPU->cpu_hat_info->hci_mutex);
                kpreempt_enable();
        } else
#endif
                x86pte_release_pagetable(dest);
}

/*
 * Called to ensure that all pagetables are in the system dump
 */
void
hat_dump(void)
{
        hat_t *hat;
        uint_t h;
        htable_t *ht;

        /*
         * Dump all page tables
         */
        for (hat = kas.a_hat; hat != NULL; hat = hat->hat_next) {
                for (h = 0; h < hat->hat_num_hash; ++h) {
                        for (ht = hat->hat_ht_hash[h]; ht; ht = ht->ht_next) {
                                if ((ht->ht_flags & HTABLE_VLP) == 0)
                                        dump_page(ht->ht_pfn);
                        }
                }
        }
}