/*      $NetBSD: uvm_fault.c,v 1.239 2026/06/23 19:29:12 skrll Exp $    */

/*
 * Copyright (c) 1997 Charles D. Cranor and Washington University.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * from: Id: uvm_fault.c,v 1.1.2.23 1998/02/06 05:29:05 chs Exp
 */

/*
 * uvm_fault.c: fault handler
 */

#include <sys/cdefs.h>
__KERNEL_RCSID(0, "$NetBSD: uvm_fault.c,v 1.239 2026/06/23 19:29:12 skrll Exp $");

#include "opt_uvmhist.h"

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/atomic.h>
#include <sys/kernel.h>
#include <sys/mman.h>

#include <uvm/uvm.h>
#include <uvm/uvm_pdpolicy.h>
#include <uvm/uvm_rndsource.h>

/*
 *
 * a word on page faults:
 *
 * types of page faults we handle:
 *
 * CASE 1: upper layer faults                   CASE 2: lower layer faults
 *
 *    CASE 1A         CASE 1B                  CASE 2A        CASE 2B
 *    read/write1     write>1                  read/write   +-cow_write/zero
 *         |             |                         |        |
 *      +--|--+       +--|--+     +-----+       +  |  +     | +-----+
 * amap |  V  |       |  ---------> new |          |        | |  ^  |
 *      +-----+       +-----+     +-----+       +  |  +     | +--|--+
 *                                                 |        |    |
 *      +-----+       +-----+                   +--|--+     | +--|--+
 * uobj | d/c |       | d/c |                   |  V  |     +----+  |
 *      +-----+       +-----+                   +-----+       +-----+
 *
 * d/c = don't care
 *
 *   case [0]: layerless fault
 *      no amap or uobj is present.   this is an error.
 *
 *   case [1]: upper layer fault [anon active]
 *     1A: [read] or [write with anon->an_ref == 1]
 *              I/O takes place in upper level anon and uobj is not touched.
 *     1B: [write with anon->an_ref > 1]
 *              new anon is alloc'd and data is copied off ["COW"]
 *
 *   case [2]: lower layer fault [uobj]
 *     2A: [read on non-NULL uobj] or [write to non-copy_on_write area]
 *              I/O takes place directly in object.
 *     2B: [write to copy_on_write] or [read on NULL uobj]
 *              data is "promoted" from uobj to a new anon.
 *              if uobj is null, then we zero fill.
 *
 * we follow the standard UVM locking protocol ordering:
 *
 * MAPS => AMAP => UOBJ => ANON => PAGE QUEUES (PQ)
 * we hold a PG_BUSY page if we unlock for I/O
 *
 *
 * the code is structured as follows:
 *
 *     - init the "IN" params in the ufi structure
 *   ReFault: (ERESTART returned to the loop in uvm_fault_internal)
 *     - do lookups [locks maps], check protection, handle needs_copy
 *     - check for case 0 fault (error)
 *     - establish "range" of fault
 *     - if we have an amap lock it and extract the anons
 *     - if sequential advice deactivate pages behind us
 *     - at the same time check pmap for unmapped areas and anon for pages
 *       that we could map in (and do map it if found)
 *     - check object for resident pages that we could map in
 *     - if (case 2) goto Case2
 *     - >>> handle case 1
 *           - ensure source anon is resident in RAM
 *           - if case 1B alloc new anon and copy from source
 *           - map the correct page in
 *   Case2:
 *     - >>> handle case 2
 *           - ensure source page is resident (if uobj)
 *           - if case 2B alloc new anon and copy from source (could be zero
 *              fill if uobj == NULL)
 *           - map the correct page in
 *     - done!
 *
 * note on paging:
 *   if we have to do I/O we place a PG_BUSY page in the correct object,
 * unlock everything, and do the I/O.   when I/O is done we must reverify
 * the state of the world before assuming that our data structures are
 * valid.   [because mappings could change while the map is unlocked]
 *
 *  alternative 1: unbusy the page in question and restart the page fault
 *    from the top (ReFault).   this is easy but does not take advantage
 *    of the information that we already have from our previous lookup,
 *    although it is possible that the "hints" in the vm_map will help here.
 *
 * alternative 2: the system already keeps track of a "version" number of
 *    a map.   [i.e. every time you write-lock a map (e.g. to change a
 *    mapping) you bump the version number up by one...]   so, we can save
 *    the version number of the map before we release the lock and start I/O.
 *    then when I/O is done we can relock and check the version numbers
 *    to see if anything changed.    this might save us some over 1 because
 *    we don't have to unbusy the page and may be less compares(?).
 *
 * alternative 3: put in backpointers or a way to "hold" part of a map
 *    in place while I/O is in progress.   this could be complex to
 *    implement (especially with structures like amap that can be referenced
 *    by multiple map entries, and figuring out what should wait could be
 *    complex as well...).
 *
 * we use alternative 2.  given that we are multi-threaded now we may want
 * to reconsider the choice.
 */

/*
 * local data structures
 */

struct uvm_advice {
        int advice;
        int nback;
        int nforw;
};

/*
 * page range array:
 * note: index in array must match "advice" value
 * XXX: borrowed numbers from freebsd.   do they work well for us?
 */

static const struct uvm_advice uvmadvice[] = {
        { UVM_ADV_NORMAL, 3, 4 },
        { UVM_ADV_RANDOM, 0, 0 },
        { UVM_ADV_SEQUENTIAL, 8, 7},
};

#define UVM_MAXRANGE 16 /* must be MAX() of nback+nforw+1 */

/*
 * private prototypes
 */

/*
 * inline functions
 */

/*
 * uvmfault_anonflush: try and deactivate pages in specified anons
 *
 * => does not have to deactivate page if it is busy
 */

static inline void
uvmfault_anonflush(struct vm_anon **anons, int n)
{
        int lcv;
        struct vm_page *pg;

        for (lcv = 0; lcv < n; lcv++) {
                if (anons[lcv] == NULL)
                        continue;
                KASSERT(rw_lock_held(anons[lcv]->an_lock));
                pg = anons[lcv]->an_page;
                if (pg && (pg->flags & PG_BUSY) == 0) {
                        uvm_pagelock(pg);
                        uvm_pagedeactivate(pg);
                        uvm_pageunlock(pg);
                }
        }
}

/*
 * normal functions
 */

/*
 * uvmfault_amapcopy: clear "needs_copy" in a map.
 *
 * => called with VM data structures unlocked (usually, see below)
 * => we get a write lock on the maps and clear needs_copy for a VA
 * => if we are out of RAM we sleep (waiting for more)
 */

static void
uvmfault_amapcopy(struct uvm_faultinfo *ufi)
{
        for (;;) {

                /*
                 * no mapping?  give up.
                 */

                if (uvmfault_lookup(ufi, true) == false)
                        return;

                /*
                 * copy if needed.
                 */

                if (UVM_ET_ISNEEDSCOPY(ufi->entry))
                        amap_copy(ufi->map, ufi->entry, AMAP_COPY_NOWAIT,
                                ufi->orig_rvaddr, ufi->orig_rvaddr + 1);

                /*
                 * didn't work?  must be out of RAM.   unlock and sleep.
                 */

                if (UVM_ET_ISNEEDSCOPY(ufi->entry)) {
                        uvmfault_unlockmaps(ufi, true);
                        uvm_wait("fltamapcopy");
                        continue;
                }

                /*
                 * got it!   unlock and return.
                 */

                uvmfault_unlockmaps(ufi, true);
                return;
        }
        /*NOTREACHED*/
}

/*
 * uvmfault_anonget: get data in an anon into a non-busy, non-released
 * page in that anon.
 *
 * => Map, amap and thus anon should be locked by caller.
 * => If we fail, we unlock everything and error is returned.
 * => If we are successful, return with everything still locked.
 * => We do not move the page on the queues [gets moved later].  If we
 *    allocate a new page [we_own], it gets put on the queues.  Either way,
 *    the result is that the page is on the queues at return time
 * => For pages which are on loan from a uvm_object (and thus are not owned
 *    by the anon): if successful, return with the owning object locked.
 *    The caller must unlock this object when it unlocks everything else.
 */

int
uvmfault_anonget(struct uvm_faultinfo *ufi, struct vm_amap *amap,
    struct vm_anon *anon)
{
        struct vm_page *pg;
        krw_t lock_type;
        int error __unused; /* used for VMSWAP */

        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);
        KASSERT(rw_lock_held(anon->an_lock));
        KASSERT(anon->an_lock == amap->am_lock);

        /* Increment the counters.*/
        cpu_count(CPU_COUNT_FLTANGET, 1);
        if (anon->an_page) {
                curlwp->l_ru.ru_minflt++;
        } else {
                curlwp->l_ru.ru_majflt++;
        }
        error = 0;

        /*
         * Loop until we get the anon data, or fail.
         */

        for (;;) {
                bool we_own, locked;
                /*
                 * Note: 'we_own' will become true if we set PG_BUSY on a page.
                 */
                we_own = false;
                pg = anon->an_page;

                /*
                 * If there is a resident page and it is loaned, then anon
                 * may not own it.  Call out to uvm_anon_lockloanpg() to
                 * identify and lock the real owner of the page.
                 */

                if (pg && pg->loan_count)
                        pg = uvm_anon_lockloanpg(anon);

                /*
                 * Is page resident?  Make sure it is not busy/released.
                 */

                lock_type = rw_lock_op(anon->an_lock);
                if (pg) {

                        /*
                         * at this point, if the page has a uobject [meaning
                         * we have it on loan], then that uobject is locked
                         * by us!   if the page is busy, we drop all the
                         * locks (including uobject) and try again.
                         */

                        if ((pg->flags & PG_BUSY) == 0) {
                                UVMHIST_LOG(maphist, "<- OK",0,0,0,0);
                                return 0;
                        }
                        cpu_count(CPU_COUNT_FLTPGWAIT, 1);

                        /*
                         * The last unlock must be an atomic unlock and wait
                         * on the owner of page.
                         */

                        if (pg->uobject) {
                                /* Owner of page is UVM object. */
                                uvmfault_unlockall(ufi, amap, NULL);
                                UVMHIST_LOG(maphist, " unlock+wait on uobj",0,
                                    0,0,0);
                                uvm_pagewait(pg, pg->uobject->vmobjlock, "anonget1");
                        } else {
                                /* Owner of page is anon. */
                                uvmfault_unlockall(ufi, NULL, NULL);
                                UVMHIST_LOG(maphist, " unlock+wait on anon",0,
                                    0,0,0);
                                uvm_pagewait(pg, anon->an_lock, "anonget2");
                        }
                } else {
#if defined(VMSWAP)
                        /*
                         * No page, therefore allocate one.  A write lock is
                         * required for this.  If the caller didn't supply
                         * one, fail now and have them retry.
                         */

                        if (lock_type == RW_READER) {
                                return ENOLCK;
                        }
                        pg = uvm_pagealloc(NULL,
                            ufi != NULL ? ufi->orig_rvaddr : 0,
                            anon, ufi != NULL ? UVM_FLAG_COLORMATCH : 0);
                        if (pg == NULL) {
                                /* Out of memory.  Wait a little. */
                                uvmfault_unlockall(ufi, amap, NULL);
                                cpu_count(CPU_COUNT_FLTNORAM, 1);
                                UVMHIST_LOG(maphist, "  noram -- UVM_WAIT",0,
                                    0,0,0);
                                if (!uvm_reclaimable()) {
                                        return ENOMEM;
                                }
                                uvm_wait("flt_noram1");
                        } else {
                                /* PG_BUSY bit is set. */
                                we_own = true;
                                uvmfault_unlockall(ufi, amap, NULL);

                                /*
                                 * Pass a PG_BUSY+PG_FAKE clean page into
                                 * the uvm_swap_get() function with all data
                                 * structures unlocked.  Note that it is OK
                                 * to read an_swslot here, because we hold
                                 * PG_BUSY on the page.
                                 */
                                cpu_count(CPU_COUNT_PAGEINS, 1);
                                error = uvm_swap_get(pg, anon->an_swslot,
                                    PGO_SYNCIO);

                                /*
                                 * We clean up after the I/O below in the
                                 * 'we_own' case.
                                 */
                        }
#else
                        panic("%s: no page", __func__);
#endif /* defined(VMSWAP) */
                }

                /*
                 * Re-lock the map and anon.
                 */

                locked = uvmfault_relock(ufi);
                if (locked || we_own) {
                        rw_enter(anon->an_lock, lock_type);
                }

                /*
                 * If we own the page (i.e. we set PG_BUSY), then we need
                 * to clean up after the I/O.  There are three cases to
                 * consider:
                 *
                 * 1) Page was released during I/O: free anon and ReFault.
                 * 2) I/O not OK.  Free the page and cause the fault to fail.
                 * 3) I/O OK!  Activate the page and sync with the non-we_own
                 *    case (i.e. drop anon lock if not locked).
                 */

                if (we_own) {
                        KASSERT(lock_type == RW_WRITER);
#if defined(VMSWAP)
                        if (error) {

                                /*
                                 * Remove the swap slot from the anon and
                                 * mark the anon as having no real slot.
                                 * Do not free the swap slot, thus preventing
                                 * it from being used again.
                                 */

                                if (anon->an_swslot > 0) {
                                        uvm_swap_markbad(anon->an_swslot, 1);
                                }
                                anon->an_swslot = SWSLOT_BAD;

                                if ((pg->flags & PG_RELEASED) != 0) {
                                        goto released;
                                }

                                /*
                                 * Note: page was never !PG_BUSY, so it
                                 * cannot be mapped and thus no need to
                                 * pmap_page_protect() it.
                                 */

                                uvm_pagefree(pg);

                                if (locked) {
                                        uvmfault_unlockall(ufi, NULL, NULL);
                                }
                                rw_exit(anon->an_lock);
                                UVMHIST_LOG(maphist, "<- ERROR", 0,0,0,0);
                                return error;
                        }

                        if ((pg->flags & PG_RELEASED) != 0) {
released:
                                KASSERT(anon->an_ref == 0);

                                /*
                                 * Released while we had unlocked amap.
                                 */

                                if (locked) {
                                        uvmfault_unlockall(ufi, NULL, NULL);
                                }
                                uvm_anon_release(anon);

                                if (error) {
                                        UVMHIST_LOG(maphist,
                                            "<- ERROR/RELEASED", 0,0,0,0);
                                        return error;
                                }

                                UVMHIST_LOG(maphist, "<- RELEASED", 0,0,0,0);
                                return ERESTART;
                        }

                        /*
                         * We have successfully read the page, activate it.
                         */

                        uvm_pagelock(pg);
                        uvm_pageactivate(pg);
                        uvm_pagewakeup(pg);
                        uvm_pageunlock(pg);
                        pg->flags &= ~(PG_BUSY|PG_FAKE);
                        uvm_pagemarkdirty(pg, UVM_PAGE_STATUS_UNKNOWN);
                        UVM_PAGE_OWN(pg, NULL);
#else
                        panic("%s: we_own", __func__);
#endif /* defined(VMSWAP) */
                }

                /*
                 * We were not able to re-lock the map - restart the fault.
                 */

                if (!locked) {
                        if (we_own) {
                                rw_exit(anon->an_lock);
                        }
                        UVMHIST_LOG(maphist, "<- REFAULT", 0,0,0,0);
                        return ERESTART;
                }

                /*
                 * Verify that no one has touched the amap and moved
                 * the anon on us.
                 */

                if (ufi != NULL && amap_lookup(&ufi->entry->aref,
                    ufi->orig_rvaddr - ufi->entry->start) != anon) {

                        uvmfault_unlockall(ufi, amap, NULL);
                        UVMHIST_LOG(maphist, "<- REFAULT", 0,0,0,0);
                        return ERESTART;
                }

                /*
                 * Retry..
                 */

                cpu_count(CPU_COUNT_FLTANRETRY, 1);
                continue;
        }
        /*NOTREACHED*/
}

/*
 * uvmfault_promote: promote data to a new anon.  used for 1B and 2B.
 *
 *      1. allocate an anon and a page.
 *      2. fill its contents.
 *      3. put it into amap.
 *
 * => if we fail (result != 0) we unlock everything.
 * => on success, return a new locked anon via 'nanon'.
 *    (*nanon)->an_page will be a resident, locked, dirty page.
 * => it's caller's responsibility to put the promoted nanon->an_page to the
 *    page queue.
 */

static int
uvmfault_promote(struct uvm_faultinfo *ufi,
    struct vm_anon *oanon,
    struct vm_page *uobjpage,
    struct vm_anon **nanon, /* OUT: allocated anon */
    struct vm_anon **spare)
{
        struct vm_amap *amap = ufi->entry->aref.ar_amap;
        struct uvm_object *uobj;
        struct vm_anon *anon;
        struct vm_page *pg;
        struct vm_page *opg;
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        if (oanon) {
                /* anon COW */
                opg = oanon->an_page;
                KASSERT(opg != NULL);
                KASSERT(opg->uobject == NULL || opg->loan_count > 0);
        } else if (uobjpage != PGO_DONTCARE) {
                /* object-backed COW */
                opg = uobjpage;
                KASSERT(rw_lock_held(opg->uobject->vmobjlock));
        } else {
                /* ZFOD */
                opg = NULL;
        }
        if (opg != NULL) {
                uobj = opg->uobject;
        } else {
                uobj = NULL;
        }

        KASSERT(amap != NULL);
        KASSERT(uobjpage != NULL);
        KASSERT(rw_write_held(amap->am_lock));
        KASSERT(oanon == NULL || amap->am_lock == oanon->an_lock);
        KASSERT(uobj == NULL || rw_lock_held(uobj->vmobjlock));

        if (*spare != NULL) {
                anon = *spare;
                *spare = NULL;
        } else {
                anon = uvm_analloc();
        }
        if (anon) {

                /*
                 * The new anon is locked.
                 *
                 * if opg == NULL, we want a zero'd, dirty page,
                 * so have uvm_pagealloc() do that for us.
                 */

                KASSERT(anon->an_lock == NULL);
                anon->an_lock = amap->am_lock;
                pg = uvm_pagealloc(NULL, ufi->orig_rvaddr, anon,
                    UVM_FLAG_COLORMATCH | (opg == NULL ? UVM_PGA_ZERO : 0));
                if (pg == NULL) {
                        anon->an_lock = NULL;
                }
        } else {
                pg = NULL;
        }

        /*
         * out of memory resources?
         */

        if (pg == NULL) {
                /* save anon for the next try. */
                if (anon != NULL) {
                        *spare = anon;
                }

                /* unlock and fail ... */
                uvmfault_unlockall(ufi, amap, uobj);
                if (!uvm_reclaimable()) {
                        UVMHIST_LOG(maphist, "out of VM", 0,0,0,0);
                        cpu_count(CPU_COUNT_FLTNOANON, 1);
                        error = ENOMEM;
                        goto done;
                }

                UVMHIST_LOG(maphist, "out of RAM, waiting for more", 0,0,0,0);
                cpu_count(CPU_COUNT_FLTNORAM, 1);
                uvm_wait("flt_noram5");
                error = ERESTART;
                goto done;
        }

        /*
         * copy the page [pg now dirty]
         *
         * Remove the pmap entry now for the old page at this address
         * so that no thread can modify the new page while any thread
         * might still see the old page.
         */
        if (opg) {
                pmap_remove(vm_map_pmap(ufi->orig_map), ufi->orig_rvaddr,
                             ufi->orig_rvaddr + PAGE_SIZE);
                pmap_update(vm_map_pmap(ufi->orig_map));
                uvm_pagecopy(opg, pg);
        }
        KASSERT(uvm_pagegetdirty(pg) == UVM_PAGE_STATUS_DIRTY);

        amap_add(&ufi->entry->aref, ufi->orig_rvaddr - ufi->entry->start, anon,
            oanon != NULL);

        /*
         * from this point on am_lock won't be dropped until the page is
         * entered, so it's safe to unbusy the page up front.
         *
         * uvm_fault_{upper,lower}_done will activate or enqueue the page.
         */

        pg = anon->an_page;
        pg->flags &= ~(PG_BUSY|PG_FAKE);
        UVM_PAGE_OWN(pg, NULL);

        *nanon = anon;
        error = 0;
done:
        return error;
}

/*
 * Update statistics after fault resolution.
 * - maxrss
 */
void
uvmfault_update_stats(struct uvm_faultinfo *ufi)
{
        struct vm_map           *map;
        struct vmspace          *vm;
        struct proc             *p;
        vsize_t                  res;

        map = ufi->orig_map;

        p = curproc;
        KASSERT(p != NULL);
        vm = p->p_vmspace;

        if (&vm->vm_map != map)
                return;

        res = pmap_resident_count(map->pmap);
        if (vm->vm_rssmax < res)
                vm->vm_rssmax = res;
}

/*
 *   F A U L T   -   m a i n   e n t r y   p o i n t
 */

/*
 * uvm_fault: page fault handler
 *
 * => called from MD code to resolve a page fault
 * => VM data structures usually should be unlocked.   however, it is
 *      possible to call here with the main map locked if the caller
 *      gets a write lock, sets it recursive, and then calls us (c.f.
 *      uvm_map_pageable).   this should be avoided because it keeps
 *      the map locked off during I/O.
 * => MUST NEVER BE CALLED IN INTERRUPT CONTEXT
 */

#define MASK(entry)     (UVM_ET_ISCOPYONWRITE(entry) ? \
                         ~VM_PROT_WRITE : VM_PROT_ALL)

/* fault_flag values passed from uvm_fault_wire to uvm_fault_internal */
#define UVM_FAULT_WIRE          (1 << 0)
#define UVM_FAULT_MAXPROT       (1 << 1)

struct uvm_faultctx {

        /*
         * the following members are set up by uvm_fault_check() and
         * read-only after that.
         *
         * note that narrow is used by uvm_fault_check() to change
         * the behaviour after ERESTART.
         *
         * most of them might change after RESTART if the underlying
         * map entry has been changed behind us.  an exception is
         * wire_paging, which does never change.
         */
        vm_prot_t access_type;
        vaddr_t startva;
        int npages;
        int centeridx;
        bool narrow;            /* work on a single requested page only */
        bool wire_mapping;      /* request a PMAP_WIRED mapping
                                   (UVM_FAULT_WIRE or VM_MAPENT_ISWIRED) */
        bool wire_paging;       /* request uvm_pagewire
                                   (true for UVM_FAULT_WIRE) */
        bool cow_now;           /* VM_PROT_WRITE is actually requested
                                   (ie. should break COW and page loaning) */

        /*
         * enter_prot is set up by uvm_fault_check() and clamped
         * (ie. drop the VM_PROT_WRITE bit) in various places in case
         * of !cow_now.
         */
        vm_prot_t enter_prot;   /* prot at which we want to enter pages in */

        /*
         * the following member is for uvmfault_promote() and ERESTART.
         */
        struct vm_anon *anon_spare;

        /*
         * the following is actually a uvm_fault_lower() internal.
         * it's here merely for debugging.
         * (or due to the mechanical separation of the function?)
         */
        bool promote;

        /*
         * type of lock to acquire on objects in both layers.
         */
        krw_t lower_lock_type;
        krw_t upper_lock_type;
};

static inline int       uvm_fault_check(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct vm_anon ***, bool);

static int              uvm_fault_upper(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct vm_anon **);
static inline int       uvm_fault_upper_lookup(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            struct vm_anon **, struct vm_page **);
static inline void      uvm_fault_upper_neighbor(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            vaddr_t, struct vm_page *, bool);
static inline int       uvm_fault_upper_loan(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct vm_anon *, struct uvm_object **);
static inline int       uvm_fault_upper_promote(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct uvm_object *, struct vm_anon *);
static inline int       uvm_fault_upper_direct(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct uvm_object *, struct vm_anon *);
static int              uvm_fault_upper_enter(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            struct uvm_object *, struct vm_anon *,
                            struct vm_page *, struct vm_anon *);
static inline void      uvm_fault_upper_done(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            struct vm_anon *, struct vm_page *);

static int              uvm_fault_lower(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct vm_page **);
static inline void      uvm_fault_lower_lookup(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            struct vm_page **);
static inline void      uvm_fault_lower_neighbor(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            vaddr_t, struct vm_page *);
static inline int       uvm_fault_lower_io(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct uvm_object **, struct vm_page **);
static inline int       uvm_fault_lower_direct(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct uvm_object *, struct vm_page *);
static inline int       uvm_fault_lower_direct_loan(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct uvm_object *, struct vm_page **,
                            struct vm_page **);
static inline int       uvm_fault_lower_promote(
                            struct uvm_faultinfo *, struct uvm_faultctx *,
                            struct uvm_object *, struct vm_page *);
static int              uvm_fault_lower_enter(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            struct uvm_object *,
                            struct vm_anon *, struct vm_page *);
static inline void      uvm_fault_lower_done(
                            struct uvm_faultinfo *, const struct uvm_faultctx *,
                            struct uvm_object *, struct vm_page *);

int
uvm_fault_internal(struct vm_map *orig_map, vaddr_t vaddr,
    vm_prot_t access_type, int fault_flag)
{
        struct uvm_faultinfo ufi;
        struct uvm_faultctx flt = {
                .access_type = access_type,

                /* don't look for neighborhood * pages on "wire" fault */
                .narrow = (fault_flag & UVM_FAULT_WIRE) != 0,

                /* "wire" fault causes wiring of both mapping and paging */
                .wire_mapping = (fault_flag & UVM_FAULT_WIRE) != 0,
                .wire_paging = (fault_flag & UVM_FAULT_WIRE) != 0,

                /*
                 * default lock type to acquire on upper & lower layer
                 * objects: reader.  this can be upgraded at any point
                 * during the fault from read -> write and uvm_faultctx
                 * changed to match, but is never downgraded write -> read.
                 */
#ifdef __HAVE_UNLOCKED_PMAP /* XXX temporary */
                .upper_lock_type = RW_WRITER,
                .lower_lock_type = RW_WRITER,
#else
                .upper_lock_type = RW_READER,
                .lower_lock_type = RW_READER,
#endif
        };
        const bool maxprot = (fault_flag & UVM_FAULT_MAXPROT) != 0;
        struct vm_anon *anons_store[UVM_MAXRANGE], **anons;
        struct vm_page *pages_store[UVM_MAXRANGE], **pages;
        int error;

        UVMHIST_FUNC(__func__);
        UVMHIST_CALLARGS(maphist, "(map=%#jx, vaddr=%#jx, at=%jd, ff=%jd)",
              (uintptr_t)orig_map, vaddr, access_type, fault_flag);

        /* Don't count anything until user interaction is possible */
        kpreempt_disable();
        if (__predict_true(start_init_exec)) {
                struct cpu_info *ci = curcpu();
                CPU_COUNT(CPU_COUNT_NFAULT, 1);
                /* Don't flood RNG subsystem with samples. */
                if (++(ci->ci_faultrng) == 503) {
                        ci->ci_faultrng = 0;
                        rnd_add_uint32(&uvm_fault_rndsource,
                            sizeof(vaddr_t) == sizeof(uint32_t) ?
                            (uint32_t)vaddr : sizeof(vaddr_t) ==
                            sizeof(uint64_t) ?
                            (uint32_t)vaddr :
                            (uint32_t)ci->ci_counts[CPU_COUNT_NFAULT]);
                }
        }
        kpreempt_enable();

        /*
         * init the IN parameters in the ufi
         */

        ufi.orig_map = orig_map;
        ufi.orig_rvaddr = trunc_page(vaddr);
        ufi.orig_size = PAGE_SIZE;      /* can't get any smaller than this */

        error = ERESTART;
        while (error == ERESTART) { /* ReFault: */
                anons = anons_store;
                pages = pages_store;

                error = uvm_fault_check(&ufi, &flt, &anons, maxprot);
                if (error != 0)
                        continue;

                error = uvm_fault_upper_lookup(&ufi, &flt, anons, pages);
                if (error != 0)
                        continue;

                if (pages[flt.centeridx] == PGO_DONTCARE)
                        error = uvm_fault_upper(&ufi, &flt, anons);
                else {
                        struct uvm_object * const uobj =
                            ufi.entry->object.uvm_obj;

                        if (uobj && uobj->pgops->pgo_fault != NULL) {
                                /*
                                 * invoke "special" fault routine.
                                 */
                                rw_enter(uobj->vmobjlock, RW_WRITER);
                                /* locked: maps(read), amap(if there), uobj */
                                error = uobj->pgops->pgo_fault(&ufi,
                                    flt.startva, pages, flt.npages,
                                    flt.centeridx, flt.access_type,
                                    PGO_LOCKED|PGO_SYNCIO);

                                /*
                                 * locked: nothing, pgo_fault has unlocked
                                 * everything
                                 */

                                /*
                                 * object fault routine responsible for
                                 * pmap_update().
                                 */

                                /*
                                 * Wake up the pagedaemon if the fault method
                                 * failed for lack of memory but some can be
                                 * reclaimed.
                                 */
                                if (error == ENOMEM && uvm_reclaimable()) {
                                        uvm_wait("pgo_fault");
                                        error = ERESTART;
                                }
                        } else {
                                error = uvm_fault_lower(&ufi, &flt, pages);
                        }
                }
        }

        if (flt.anon_spare != NULL) {
                flt.anon_spare->an_ref--;
                KASSERT(flt.anon_spare->an_ref == 0);
                KASSERT(flt.anon_spare->an_lock == NULL);
                uvm_anfree(flt.anon_spare);
        }
        return error;
}

/*
 * uvm_fault_check: check prot, handle needs-copy, etc.
 *
 *      1. lookup entry.
 *      2. check protection.
 *      3. adjust fault condition (mainly for simulated fault).
 *      4. handle needs-copy (lazy amap copy).
 *      5. establish range of interest for neighbor fault (aka pre-fault).
 *      6. look up anons (if amap exists).
 *      7. flush pages (if MADV_SEQUENTIAL)
 *
 * => called with nothing locked.
 * => if we fail (result != 0) we unlock everything.
 * => initialize/adjust many members of flt.
 */

static int
uvm_fault_check(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct vm_anon ***ranons, bool maxprot)
{
        struct vm_amap *amap;
        struct uvm_object *uobj;
        vm_prot_t check_prot;
        int nback, nforw;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /*
         * lookup and lock the maps
         */

        if (uvmfault_lookup(ufi, false) == false) {
                UVMHIST_LOG(maphist, "<- no mapping @ %#jx", ufi->orig_rvaddr,
                    0,0,0);
                return EFAULT;
        }
        /* locked: maps(read) */

#ifdef DIAGNOSTIC
        if ((ufi->map->flags & VM_MAP_PAGEABLE) == 0) {
                printf("Page fault on non-pageable map:\n");
                printf("ufi->map = %p\n", ufi->map);
                printf("ufi->orig_map = %p\n", ufi->orig_map);
                printf("ufi->orig_rvaddr = %#lx\n", (u_long) ufi->orig_rvaddr);
                panic("uvm_fault: (ufi->map->flags & VM_MAP_PAGEABLE) == 0");
        }
#endif

        /*
         * check protection
         */

        check_prot = maxprot ?
            ufi->entry->max_protection : ufi->entry->protection;
        if ((check_prot & flt->access_type) != flt->access_type) {
                UVMHIST_LOG(maphist,
                    "<- protection failure (prot=%#jx, access=%#jx)",
                    ufi->entry->protection, flt->access_type, 0, 0);
                uvmfault_unlockmaps(ufi, false);
                return EFAULT;
        }

        /*
         * "enter_prot" is the protection we want to enter the page in at.
         * for certain pages (e.g. copy-on-write pages) this protection can
         * be more strict than ufi->entry->protection.  "wired" means either
         * the entry is wired or we are fault-wiring the pg.
         */

        flt->enter_prot = ufi->entry->protection;
        if (VM_MAPENT_ISWIRED(ufi->entry)) {
                flt->wire_mapping = true;
                flt->wire_paging = true;
                flt->narrow = true;
        }

        if (flt->wire_mapping) {
                flt->access_type = flt->enter_prot; /* full access for wired */
                flt->cow_now = (check_prot & VM_PROT_WRITE) != 0;
        } else {
                flt->cow_now = (flt->access_type & VM_PROT_WRITE) != 0;
        }

        if (flt->wire_paging) {
                /* wiring pages requires a write lock. */
                flt->upper_lock_type = RW_WRITER;
                flt->lower_lock_type = RW_WRITER;
        }

        flt->promote = false;

        /*
         * handle "needs_copy" case.   if we need to copy the amap we will
         * have to drop our readlock and relock it with a write lock.  (we
         * need a write lock to change anything in a map entry [e.g.
         * needs_copy]).
         */

        if (UVM_ET_ISNEEDSCOPY(ufi->entry)) {
                if (flt->cow_now || (ufi->entry->object.uvm_obj == NULL)) {
                        KASSERT(!maxprot);
                        /* need to clear */
                        UVMHIST_LOG(maphist,
                            "  need to clear needs_copy and refault",0,0,0,0);
                        uvmfault_unlockmaps(ufi, false);
                        uvmfault_amapcopy(ufi);
                        cpu_count(CPU_COUNT_FLTAMCOPY, 1);
                        return ERESTART;

                } else {

                        /*
                         * ensure that we pmap_enter page R/O since
                         * needs_copy is still true
                         */

                        flt->enter_prot &= ~VM_PROT_WRITE;
                }
        }

        /*
         * identify the players
         */

        amap = ufi->entry->aref.ar_amap;        /* upper layer */
        uobj = ufi->entry->object.uvm_obj;      /* lower layer */

        /*
         * check for a case 0 fault.  if nothing backing the entry then
         * error now.
         */

        if (amap == NULL && uobj == NULL) {
                uvmfault_unlockmaps(ufi, false);
                UVMHIST_LOG(maphist,"<- no backing store, no overlay",0,0,0,0);
                return EFAULT;
        }

        /*
         * for a case 2B fault waste no time on adjacent pages because
         * they are likely already entered.
         */

        if (uobj != NULL && amap != NULL &&
            (flt->access_type & VM_PROT_WRITE) != 0) {
                /* wide fault (!narrow) */
                flt->narrow = true;
        }

        /*
         * establish range of interest based on advice from mapper
         * and then clip to fit map entry.   note that we only want
         * to do this the first time through the fault.   if we
         * ReFault we will disable this by setting "narrow" to true.
         */

        if (flt->narrow == false) {

                /* wide fault (!narrow) */
                KASSERT(uvmadvice[ufi->entry->advice].advice ==
                         ufi->entry->advice);
                nback = MIN(uvmadvice[ufi->entry->advice].nback,
                    (ufi->orig_rvaddr - ufi->entry->start) >> PAGE_SHIFT);
                flt->startva = ufi->orig_rvaddr - (nback << PAGE_SHIFT);
                /*
                 * note: "-1" because we don't want to count the
                 * faulting page as forw
                 */
                nforw = MIN(uvmadvice[ufi->entry->advice].nforw,
                            ((ufi->entry->end - ufi->orig_rvaddr) >>
                             PAGE_SHIFT) - 1);
                flt->npages = nback + nforw + 1;
                flt->centeridx = nback;

                flt->narrow = true;     /* ensure only once per-fault */

        } else {

                /* narrow fault! */
                nback = nforw = 0;
                flt->startva = ufi->orig_rvaddr;
                flt->npages = 1;
                flt->centeridx = 0;

        }
        /* offset from entry's start to pgs' start */
        const voff_t eoff = flt->startva - ufi->entry->start;

        /* locked: maps(read) */
        UVMHIST_LOG(maphist, "  narrow=%jd, back=%jd, forw=%jd, startva=%#jx",
                    flt->narrow, nback, nforw, flt->startva);
        UVMHIST_LOG(maphist, "  entry=%#jx, amap=%#jx, obj=%#jx",
            (uintptr_t)ufi->entry, (uintptr_t)amap, (uintptr_t)uobj, 0);

        /*
         * guess at the most suitable lock types to acquire.
         * if we've got an amap then lock it and extract current anons.
         */

        if (amap) {
                if ((amap_flags(amap) & AMAP_SHARED) == 0) {
                        /*
                         * the amap isn't shared.  get a writer lock to
                         * avoid the cost of upgrading the lock later if
                         * needed.
                         *
                         * XXX nice for PostgreSQL, but consider threads.
                         */
                        flt->upper_lock_type = RW_WRITER;
                } else if ((flt->access_type & VM_PROT_WRITE) != 0) {
                        /*
                         * assume we're about to COW.
                         */
                        flt->upper_lock_type = RW_WRITER;
                }
                amap_lock(amap, flt->upper_lock_type);
                amap_lookups(&ufi->entry->aref, eoff, *ranons, flt->npages);
        } else {
                if ((flt->access_type & VM_PROT_WRITE) != 0) {
                        /*
                         * we are about to dirty the object and that
                         * requires a write lock.
                         */
                        flt->lower_lock_type = RW_WRITER;
                }
                *ranons = NULL; /* to be safe */
        }

        /* locked: maps(read), amap(if there) */
        KASSERT(amap == NULL ||
            rw_lock_op(amap->am_lock) == flt->upper_lock_type);

        /*
         * for MADV_SEQUENTIAL mappings we want to deactivate the back pages
         * now and then forget about them (for the rest of the fault).
         */

        if (ufi->entry->advice == MADV_SEQUENTIAL && nback != 0) {

                UVMHIST_LOG(maphist, "  MADV_SEQUENTIAL: flushing backpages",
                    0,0,0,0);
                /* flush back-page anons? */
                if (amap)
                        uvmfault_anonflush(*ranons, nback);

                /*
                 * flush object?  change lock type to RW_WRITER, to avoid
                 * excessive competition between read/write locks if many
                 * threads doing "sequential access".
                 */
                if (uobj) {
                        voff_t uoff;

                        flt->lower_lock_type = RW_WRITER;
                        uoff = ufi->entry->offset + eoff;
                        rw_enter(uobj->vmobjlock, RW_WRITER);
                        (void) (uobj->pgops->pgo_put)(uobj, uoff, uoff +
                                    (nback << PAGE_SHIFT), PGO_DEACTIVATE);
                }

                /* now forget about the backpages */
                if (amap)
                        *ranons += nback;
                flt->startva += (nback << PAGE_SHIFT);
                flt->npages -= nback;
                flt->centeridx = 0;
        }
        /*
         * => startva is fixed
         * => npages is fixed
         */
        KASSERT(flt->startva <= ufi->orig_rvaddr);
        KASSERT(ufi->orig_rvaddr + ufi->orig_size <=
            flt->startva + (flt->npages << PAGE_SHIFT));
        return 0;
}

/*
 * uvm_fault_upper_upgrade: upgrade upper lock, reader -> writer
 */

static inline int
uvm_fault_upper_upgrade(struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
    struct vm_amap *amap, struct uvm_object *uobj)
{
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        KASSERT(amap != NULL);
        KASSERT(flt->upper_lock_type == rw_lock_op(amap->am_lock));

        /*
         * fast path.
         */

        if (__predict_true(flt->upper_lock_type == RW_WRITER)) {
                return 0;
        }

        /*
         * otherwise try for the upgrade.  if we don't get it, unlock
         * everything, restart the fault and next time around get a writer
         * lock.
         */

        flt->upper_lock_type = RW_WRITER;
        if (__predict_false(!rw_tryupgrade(amap->am_lock))) {
                uvmfault_unlockall(ufi, amap, uobj);
                cpu_count(CPU_COUNT_FLTNOUP, 1);
                UVMHIST_LOG(maphist, "  !upgrade upper", 0, 0,0,0);
                return ERESTART;
        }
        cpu_count(CPU_COUNT_FLTUP, 1);
        KASSERT(flt->upper_lock_type == rw_lock_op(amap->am_lock));
        return 0;
}

/*
 * uvm_fault_upper_lookup: look up existing h/w mapping and amap.
 *
 * iterate range of interest:
 *      1. check if h/w mapping exists.  if yes, we don't care
 *      2. check if anon exists.  if not, page is lower.
 *      3. if anon exists, enter h/w mapping for neighbors.
 *
 * => called with amap locked (if exists).
 */

static int
uvm_fault_upper_lookup(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        struct vm_anon **anons, struct vm_page **pages)
{
        struct vm_amap *amap = ufi->entry->aref.ar_amap;
        int lcv;
        vaddr_t currva;
        bool shadowed __unused;
        bool entered;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /* locked: maps(read), amap(if there) */
        KASSERT(amap == NULL ||
            rw_lock_op(amap->am_lock) == flt->upper_lock_type);

        /*
         * map in the backpages and frontpages we found in the amap in hopes
         * of preventing future faults.    we also init the pages[] array as
         * we go.
         */

        currva = flt->startva;
        shadowed = false;
        entered = false;
        for (lcv = 0; lcv < flt->npages; lcv++, currva += PAGE_SIZE) {
                /*
                 * unmapped or center page.   check if any anon at this level.
                 */
                if (amap == NULL || anons[lcv] == NULL) {
                        pages[lcv] = NULL;
                        continue;
                }

                /*
                 * check for present page and map if possible.
                 */

                pages[lcv] = PGO_DONTCARE;
                if (lcv == flt->centeridx) {    /* save center for later! */
                        shadowed = true;
                        continue;
                }

                struct vm_anon *anon = anons[lcv];
                struct vm_page *pg = anon->an_page;

                KASSERT(anon->an_lock == amap->am_lock);

                /*
                 * ignore loaned and busy pages.
                 * don't play with VAs that are already mapped.
                 */

                if (pg && pg->loan_count == 0 && (pg->flags & PG_BUSY) == 0 &&
                    !pmap_extract(ufi->orig_map->pmap, currva, NULL)) {
                        uvm_fault_upper_neighbor(ufi, flt, currva,
                            pg, anon->an_ref > 1);
                        entered = true;
                }
        }
        if (entered) {
                pmap_update(ufi->orig_map->pmap);
        }

        /* locked: maps(read), amap(if there) */
        KASSERT(amap == NULL ||
            rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        /* (shadowed == true) if there is an anon at the faulting address */
        UVMHIST_LOG(maphist, "  shadowed=%jd, will_get=%jd", shadowed,
            (ufi->entry->object.uvm_obj && shadowed != false),0,0);

        return 0;
}

/*
 * uvm_fault_upper_neighbor: enter single upper neighbor page.
 *
 * => called with amap and anon locked.
 */

static void
uvm_fault_upper_neighbor(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        vaddr_t currva, struct vm_page *pg, bool readonly)
{
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /* locked: amap, anon */

        KASSERT(pg->uobject == NULL);
        KASSERT(pg->uanon != NULL);
        KASSERT(rw_lock_op(pg->uanon->an_lock) == flt->upper_lock_type);
        KASSERT(uvm_pagegetdirty(pg) != UVM_PAGE_STATUS_CLEAN);

        /*
         * there wasn't a direct fault on the page, so avoid the cost of
         * activating it.
         */

        if (!uvmpdpol_pageisqueued_p(pg) && pg->wire_count == 0) {
                uvm_pagelock(pg);
                uvm_pageenqueue(pg);
                uvm_pageunlock(pg);
        }

        UVMHIST_LOG(maphist,
            "  MAPPING: n anon: pm=%#jx, va=%#jx, pg=%#jx",
            (uintptr_t)ufi->orig_map->pmap, currva, (uintptr_t)pg, 0);
        cpu_count(CPU_COUNT_FLTNAMAP, 1);

        /*
         * Since this page isn't the page that's actually faulting,
         * ignore pmap_enter() failures; it's not critical that we
         * enter these right now.
         */

        (void) pmap_enter(ufi->orig_map->pmap, currva,
            VM_PAGE_TO_PHYS(pg),
            readonly ? (flt->enter_prot & ~VM_PROT_WRITE) :
            flt->enter_prot,
            PMAP_CANFAIL | (flt->wire_mapping ? PMAP_WIRED : 0));
}

/*
 * uvm_fault_upper: handle upper fault.
 *
 *      1. acquire anon lock.
 *      2. get anon.  let uvmfault_anonget do the dirty work.
 *      3. handle loan.
 *      4. dispatch direct or promote handlers.
 */

static int
uvm_fault_upper(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct vm_anon **anons)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        struct vm_anon * const anon = anons[flt->centeridx];
        struct uvm_object *uobj;
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /* locked: maps(read), amap, anon */
        KASSERT(rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        KASSERT(anon->an_lock == amap->am_lock);

        /*
         * handle case 1: fault on an anon in our amap
         */

        UVMHIST_LOG(maphist, "  case 1 fault: anon=%#jx",
            (uintptr_t)anon, 0, 0, 0);

        /*
         * no matter if we have case 1A or case 1B we are going to need to
         * have the anon's memory resident.   ensure that now.
         */

        /*
         * let uvmfault_anonget do the dirty work.
         * if it fails (!OK) it will unlock everything for us.
         * if it succeeds, locks are still valid and locked.
         * also, if it is OK, then the anon's page is on the queues.
         * if the page is on loan from a uvm_object, then anonget will
         * lock that object for us if it does not fail.
         */
 retry:
        error = uvmfault_anonget(ufi, amap, anon);
        switch (error) {
        case 0:
                break;

        case ERESTART:
                return ERESTART;

        case EAGAIN:
                kpause("fltagain1", false, hz/2, NULL);
                return ERESTART;

        case ENOLCK:
                /* it needs a write lock: retry */
                error = uvm_fault_upper_upgrade(ufi, flt, amap, NULL);
                if (error != 0) {
                        return error;
                }
                KASSERT(rw_write_held(amap->am_lock));
                goto retry;

        default:
                return error;
        }

        /*
         * uobj is non null if the page is on loan from an object (i.e. uobj)
         */

        uobj = anon->an_page->uobject;  /* locked by anonget if !NULL */

        /* locked: maps(read), amap, anon, uobj(if one) */
        KASSERT(rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        KASSERT(anon->an_lock == amap->am_lock);
        KASSERT(uobj == NULL ||
            rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);

        /*
         * special handling for loaned pages
         */

        if (anon->an_page->loan_count) {
                error = uvm_fault_upper_loan(ufi, flt, anon, &uobj);
                if (error != 0)
                        return error;
        }

        /*
         * if we are case 1B then we will need to allocate a new blank
         * anon to transfer the data into.   note that we have a lock
         * on anon, so no one can busy or release the page until we are done.
         * also note that the ref count can't drop to zero here because
         * it is > 1 and we are only dropping one ref.
         *
         * in the (hopefully very rare) case that we are out of RAM we
         * will unlock, wait for more RAM, and refault.
         *
         * if we are out of anon VM we kill the process (XXX: could wait?).
         */

        if (flt->cow_now && anon->an_ref > 1) {
                flt->promote = true;
                error = uvm_fault_upper_promote(ufi, flt, uobj, anon);
        } else {
                error = uvm_fault_upper_direct(ufi, flt, uobj, anon);
        }
        return error;
}

/*
 * uvm_fault_upper_loan: handle loaned upper page.
 *
 *      1. if not cow'ing now, simply adjust flt->enter_prot.
 *      2. if cow'ing now, and if ref count is 1, break loan.
 */

static int
uvm_fault_upper_loan(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct vm_anon *anon, struct uvm_object **ruobj)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        int error = 0;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        if (!flt->cow_now) {

                /*
                 * for read faults on loaned pages we just cap the
                 * protection at read-only.
                 */

                flt->enter_prot = flt->enter_prot & ~VM_PROT_WRITE;

        } else {
                /*
                 * note that we can't allow writes into a loaned page!
                 *
                 * if we have a write fault on a loaned page in an
                 * anon then we need to look at the anon's ref count.
                 * if it is greater than one then we are going to do
                 * a normal copy-on-write fault into a new anon (this
                 * is not a problem).  however, if the reference count
                 * is one (a case where we would normally allow a
                 * write directly to the page) then we need to kill
                 * the loan before we continue.
                 */

                /* >1 case is already ok */
                if (anon->an_ref == 1) {
                        /* breaking loan requires a write lock. */
                        error = uvm_fault_upper_upgrade(ufi, flt, amap, NULL);
                        if (error != 0) {
                                return error;
                        }
                        KASSERT(rw_write_held(amap->am_lock));

                        error = uvm_loanbreak_anon(anon, *ruobj);
                        if (error != 0) {
                                uvmfault_unlockall(ufi, amap, *ruobj);
                                uvm_wait("flt_noram2");
                                return ERESTART;
                        }
                        /* if we were a loan receiver uobj is gone */
                        if (*ruobj)
                                *ruobj = NULL;
                }
        }
        return error;
}

/*
 * uvm_fault_upper_promote: promote upper page.
 *
 *      1. call uvmfault_promote.
 *      2. enqueue page.
 *      3. deref.
 *      4. pass page to uvm_fault_upper_enter.
 */

static int
uvm_fault_upper_promote(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_anon *anon)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        struct vm_anon * const oanon = anon;
        struct vm_page *pg;
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        UVMHIST_LOG(maphist, "  case 1B: COW fault",0,0,0,0);

        /* promoting requires a write lock. */
        error = uvm_fault_upper_upgrade(ufi, flt, amap, NULL);
        if (error != 0) {
                return error;
        }
        KASSERT(rw_write_held(amap->am_lock));

        cpu_count(CPU_COUNT_FLT_ACOW, 1);

        error = uvmfault_promote(ufi, oanon, PGO_DONTCARE, &anon,
            &flt->anon_spare);
        switch (error) {
        case 0:
                break;
        case ERESTART:
                return ERESTART;
        default:
                return error;
        }
        pg = anon->an_page;

        KASSERT(anon->an_lock == oanon->an_lock);
        KASSERT((pg->flags & (PG_BUSY | PG_FAKE)) == 0);

        /* deref: can not drop to zero here by defn! */
        KASSERT(oanon->an_ref > 1);
        oanon->an_ref--;

        /*
         * note: oanon is still locked, as is the new anon.  we
         * need to check for this later when we unlock oanon; if
         * oanon != anon, we'll have to unlock anon, too.
         */

        return uvm_fault_upper_enter(ufi, flt, uobj, anon, pg, oanon);
}

/*
 * uvm_fault_upper_direct: handle direct fault.
 */

static int
uvm_fault_upper_direct(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_anon *anon)
{
        struct vm_anon * const oanon = anon;
        struct vm_page *pg;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        cpu_count(CPU_COUNT_FLT_ANON, 1);
        pg = anon->an_page;
        if (anon->an_ref > 1)     /* disallow writes to ref > 1 anons */
                flt->enter_prot = flt->enter_prot & ~VM_PROT_WRITE;

        return uvm_fault_upper_enter(ufi, flt, uobj, anon, pg, oanon);
}

/*
 * uvm_fault_upper_enter: enter h/w mapping of upper page.
 */

static int
uvm_fault_upper_enter(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_anon *anon, struct vm_page *pg,
        struct vm_anon *oanon)
{
        struct pmap *pmap = ufi->orig_map->pmap;
        vaddr_t va = ufi->orig_rvaddr;
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /* locked: maps(read), amap, oanon, anon(if different from oanon) */
        KASSERT(rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        KASSERT(anon->an_lock == amap->am_lock);
        KASSERT(oanon->an_lock == amap->am_lock);
        KASSERT(uobj == NULL ||
            rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);
        KASSERT(uvm_pagegetdirty(pg) != UVM_PAGE_STATUS_CLEAN);

        /*
         * now map the page in.
         */

        UVMHIST_LOG(maphist,
            "  MAPPING: anon: pm=%#jx, va=%#jx, pg=%#jx, promote=%jd",
            (uintptr_t)pmap, va, (uintptr_t)pg, flt->promote);
        if (pmap_enter(pmap, va, VM_PAGE_TO_PHYS(pg),
            flt->enter_prot, flt->access_type | PMAP_CANFAIL |
            (flt->wire_mapping ? PMAP_WIRED : 0)) != 0) {

                /*
                 * If pmap_enter() fails, it must not leave behind an existing
                 * pmap entry.  In particular, a now-stale entry for a different
                 * page would leave the pmap inconsistent with the vm_map.
                 * This is not to imply that pmap_enter() should remove an
                 * existing mapping in such a situation (since that could create
                 * different problems, eg. if the existing mapping is wired),
                 * but rather that the pmap should be designed such that it
                 * never needs to fail when the new mapping is replacing an
                 * existing mapping and the new page has no existing mappings.
                 *
                 * XXX This can't be asserted safely any more because many
                 * LWPs and/or many processes could simultaneously fault on
                 * the same VA and some might succeed.
                 */

                /* KASSERT(!pmap_extract(pmap, va, NULL)); */

                /*
                 * ensure that the page is queued in the case that
                 * we just promoted.
                 */

                uvm_pagelock(pg);
                uvm_pageenqueue(pg);
                uvm_pageunlock(pg);

                /*
                 * No need to undo what we did; we can simply think of
                 * this as the pmap throwing away the mapping information.
                 *
                 * We do, however, have to go through the ReFault path,
                 * as the map may change while we're asleep.
                 */

                uvmfault_unlockall(ufi, amap, uobj);
                if (!uvm_reclaimable()) {
                        UVMHIST_LOG(maphist,
                            "<- failed.  out of VM",0,0,0,0);
                        /* XXX instrumentation */
                        return ENOMEM;
                }
                /* XXX instrumentation */
                uvm_wait("flt_pmfail1");
                return ERESTART;
        }

        uvm_fault_upper_done(ufi, flt, anon, pg);

        /*
         * done case 1!  finish up by unlocking everything and returning success
         */

        pmap_update(pmap);
        uvmfault_unlockall(ufi, amap, uobj);
        return 0;
}

/*
 * uvm_fault_upper_done: queue upper center page.
 */

static void
uvm_fault_upper_done(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        struct vm_anon *anon, struct vm_page *pg)
{
        const bool wire_paging = flt->wire_paging;

        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /*
         * ... update the page queues.
         */

        if (wire_paging) {
                uvm_pagelock(pg);
                uvm_pagewire(pg);
                uvm_pageunlock(pg);

                /*
                 * since the now-wired page cannot be paged out,
                 * release its swap resources for others to use.
                 * and since an anon with no swap cannot be clean,
                 * mark it dirty now.
                 */

                uvm_pagemarkdirty(pg, UVM_PAGE_STATUS_DIRTY);
                uvm_anon_dropswap(anon);
        } else if (uvmpdpol_pageactivate_p(pg)) {
                /*
                 * avoid re-activating the page unless needed,
                 * to avoid false sharing on multiprocessor.
                 */

                uvm_pagelock(pg);
                uvm_pageactivate(pg);
                uvm_pageunlock(pg);
        }
}

/*
 * uvm_fault_lower_upgrade: upgrade lower lock, reader -> writer
 */

static inline int
uvm_fault_lower_upgrade(struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
    struct vm_amap *amap, struct uvm_object *uobj, struct vm_page *uobjpage)
{

        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        KASSERT(uobj != NULL);
        KASSERT(flt->lower_lock_type == rw_lock_op(uobj->vmobjlock));

        /*
         * fast path.
         */

        if (__predict_true(flt->lower_lock_type == RW_WRITER)) {
                return 0;
        }

        /*
         * otherwise try for the upgrade.  if we don't get it, unlock
         * everything, restart the fault and next time around get a writer
         * lock.
         */

        flt->lower_lock_type = RW_WRITER;
        if (__predict_false(!rw_tryupgrade(uobj->vmobjlock))) {
                uvmfault_unlockall(ufi, amap, uobj);
                cpu_count(CPU_COUNT_FLTNOUP, 1);
                UVMHIST_LOG(maphist, "  !upgrade lower", 0, 0,0,0);
                return ERESTART;
        }
        cpu_count(CPU_COUNT_FLTUP, 1);
        KASSERT(flt->lower_lock_type == rw_lock_op(uobj->vmobjlock));
        return 0;
}

/*
 * uvm_fault_lower: handle lower fault.
 *
 *      1. check uobj
 *      1.1. if null, ZFOD.
 *      1.2. if not null, look up unmapped neighbor pages.
 *      2. for center page, check if promote.
 *      2.1. ZFOD always needs promotion.
 *      2.2. other uobjs, when entry is marked COW (usually MAP_PRIVATE vnode).
 *      3. if uobj is not ZFOD and page is not found, do i/o.
 *      4. dispatch either direct / promote fault.
 */

static int
uvm_fault_lower(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct vm_page **pages)
{
        struct vm_amap *amap __diagused = ufi->entry->aref.ar_amap;
        struct uvm_object *uobj = ufi->entry->object.uvm_obj;
        struct vm_page *uobjpage;
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /*
         * now, if the desired page is not shadowed by the amap and we have
         * a backing object that does not have a special fault routine, then
         * we ask (with pgo_get) the object for resident pages that we care
         * about and attempt to map them in.  we do not let pgo_get block
         * (PGO_LOCKED).
         */

        if (uobj == NULL) {
                /* zero fill; don't care neighbor pages */
                uobjpage = NULL;
        } else {
                uvm_fault_lower_lookup(ufi, flt, pages);
                uobjpage = pages[flt->centeridx];
        }

        /*
         * note that at this point we are done with any front or back pages.
         * we are now going to focus on the center page (i.e. the one we've
         * faulted on).  if we have faulted on the upper (anon) layer
         * [i.e. case 1], then the anon we want is anons[centeridx] (we have
         * not touched it yet).  if we have faulted on the bottom (uobj)
         * layer [i.e. case 2] and the page was both present and available,
         * then we've got a pointer to it as "uobjpage" and we've already
         * made it BUSY.
         */

        /*
         * locked:
         * maps(read), amap(if there), uobj(if !null), uobjpage(if !null)
         */
        KASSERT(amap == NULL ||
            rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        KASSERT(uobj == NULL ||
            rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);

        /*
         * note that uobjpage can not be PGO_DONTCARE at this point.  we now
         * set uobjpage to PGO_DONTCARE if we are doing a zero fill.  if we
         * have a backing object, check and see if we are going to promote
         * the data up to an anon during the fault.
         */

        if (uobj == NULL) {
                uobjpage = PGO_DONTCARE;
                flt->promote = true;            /* always need anon here */
        } else {
                KASSERT(uobjpage != PGO_DONTCARE);
                flt->promote = flt->cow_now && UVM_ET_ISCOPYONWRITE(ufi->entry);
        }
        UVMHIST_LOG(maphist, "  case 2 fault: promote=%jd, zfill=%jd",
            flt->promote, (uobj == NULL), 0,0);

        /*
         * if uobjpage is not null then we do not need to do I/O to get the
         * uobjpage.
         *
         * if uobjpage is null, then we need to unlock and ask the pager to
         * get the data for us.   once we have the data, we need to reverify
         * the state the world.   we are currently not holding any resources.
         */

        if (uobjpage) {
                /* update rusage counters */
                curlwp->l_ru.ru_minflt++;
        } else {
                error = uvm_fault_lower_io(ufi, flt, &uobj, &uobjpage);
                if (error != 0)
                        return error;
        }

        /*
         * locked:
         * maps(read), amap(if !null), uobj(if !null), uobjpage(if uobj)
         */
        KASSERT(amap == NULL ||
            rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        KASSERT(uobj == NULL ||
            rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);

        /*
         * notes:
         *  - at this point uobjpage can not be NULL
         *  - at this point uobjpage can not be PG_RELEASED (since we checked
         *  for it above)
         *  - at this point uobjpage could be waited on (handle later)
         *  - uobjpage can be from a different object if tmpfs (vnode vs UAO)
         */

        KASSERT(uobjpage != NULL);
        KASSERT(uobj == NULL ||
            uobjpage->uobject->vmobjlock == uobj->vmobjlock);
        KASSERT(uobj == NULL || !UVM_OBJ_IS_CLEAN(uobjpage->uobject) ||
            uvm_pagegetdirty(uobjpage) == UVM_PAGE_STATUS_CLEAN);

        if (!flt->promote) {
                error = uvm_fault_lower_direct(ufi, flt, uobj, uobjpage);
        } else {
                error = uvm_fault_lower_promote(ufi, flt, uobj, uobjpage);
        }
        return error;
}

/*
 * uvm_fault_lower_lookup: look up on-memory uobj pages.
 *
 *      1. get on-memory pages.
 *      2. if failed, give up (get only center page later).
 *      3. if succeeded, enter h/w mapping of neighbor pages.
 */

static void
uvm_fault_lower_lookup(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        struct vm_page **pages)
{
        struct uvm_object *uobj = ufi->entry->object.uvm_obj;
        int lcv, gotpages;
        vaddr_t currva;
        bool entered;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        rw_enter(uobj->vmobjlock, flt->lower_lock_type);

        /*
         * Locked: maps(read), amap(if there), uobj
         */

        cpu_count(CPU_COUNT_FLTLGET, 1);
        gotpages = flt->npages;
        (void) uobj->pgops->pgo_get(uobj,
            ufi->entry->offset + flt->startva - ufi->entry->start,
            pages, &gotpages, flt->centeridx,
            flt->access_type & MASK(ufi->entry), ufi->entry->advice,
            PGO_LOCKED);

        KASSERT(rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);

        /*
         * check for pages to map, if we got any
         */

        if (gotpages == 0) {
                pages[flt->centeridx] = NULL;
                return;
        }

        entered = false;
        currva = flt->startva;
        for (lcv = 0; lcv < flt->npages; lcv++, currva += PAGE_SIZE) {
                struct vm_page *curpg;

                curpg = pages[lcv];
                if (curpg == NULL || curpg == PGO_DONTCARE) {
                        continue;
                }

                /*
                 * in the case of tmpfs, the pages might be from a different
                 * uvm_object.  just make sure that they have the same lock.
                 */

                KASSERT(curpg->uobject->vmobjlock == uobj->vmobjlock);
                KASSERT((curpg->flags & PG_BUSY) == 0);

                /*
                 * leave the centre page for later.  don't screw with
                 * existing mappings (needless & expensive).
                 */

                if (lcv == flt->centeridx) {
                        UVMHIST_LOG(maphist, "  got uobjpage (%#jx) "
                            "with locked get", (uintptr_t)curpg, 0, 0, 0);
                } else if (!pmap_extract(ufi->orig_map->pmap, currva, NULL)) {
                        uvm_fault_lower_neighbor(ufi, flt, currva, curpg);
                        entered = true;
                }
        }
        if (entered) {
                pmap_update(ufi->orig_map->pmap);
        }
}

/*
 * uvm_fault_lower_neighbor: enter h/w mapping of lower neighbor page.
 */

static void
uvm_fault_lower_neighbor(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        vaddr_t currva, struct vm_page *pg)
{
        const bool readonly = uvm_pagereadonly_p(pg) || pg->loan_count > 0;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /* locked: maps(read), amap(if there), uobj */

        /*
         * calling pgo_get with PGO_LOCKED returns us pages which
         * are neither busy nor released, so we don't need to check
         * for this.  we can just directly enter the pages.
         *
         * there wasn't a direct fault on the page, so avoid the cost of
         * activating it.
         */

        if (!uvmpdpol_pageisqueued_p(pg) && pg->wire_count == 0) {
                uvm_pagelock(pg);
                uvm_pageenqueue(pg);
                uvm_pageunlock(pg);
        }

        UVMHIST_LOG(maphist,
            "  MAPPING: n obj: pm=%#jx, va=%#jx, pg=%#jx",
            (uintptr_t)ufi->orig_map->pmap, currva, (uintptr_t)pg, 0);
        cpu_count(CPU_COUNT_FLTNOMAP, 1);

        /*
         * Since this page isn't the page that's actually faulting,
         * ignore pmap_enter() failures; it's not critical that we
         * enter these right now.
         * NOTE: page can't be waited on or PG_RELEASED because we've
         * held the lock the whole time we've had the handle.
         */
        KASSERT((pg->flags & PG_PAGEOUT) == 0);
        KASSERT((pg->flags & PG_RELEASED) == 0);
        KASSERT(!UVM_OBJ_IS_CLEAN(pg->uobject) ||
            uvm_pagegetdirty(pg) == UVM_PAGE_STATUS_CLEAN);
        KASSERT((pg->flags & PG_BUSY) == 0);
        KASSERT(rw_lock_op(pg->uobject->vmobjlock) == flt->lower_lock_type);

        const vm_prot_t mapprot =
            readonly ? (flt->enter_prot & ~VM_PROT_WRITE) :
            flt->enter_prot & MASK(ufi->entry);
        const u_int mapflags =
            PMAP_CANFAIL | (flt->wire_mapping ? (mapprot | PMAP_WIRED) : 0);
        (void) pmap_enter(ufi->orig_map->pmap, currva,
            VM_PAGE_TO_PHYS(pg), mapprot, mapflags);
}

/*
 * uvm_fault_lower_io: get lower page from backing store.
 *
 *      1. unlock everything, because i/o will block.
 *      2. call pgo_get.
 *      3. if failed, recover.
 *      4. if succeeded, relock everything and verify things.
 */

static int
uvm_fault_lower_io(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct uvm_object **ruobj, struct vm_page **ruobjpage)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        struct uvm_object *uobj = *ruobj;
        struct vm_page *pg;
        bool locked;
        int gotpages;
        int error;
        voff_t uoff;
        vm_prot_t access_type;
        int advice;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /* grab everything we need from the entry before we unlock */
        uoff = (ufi->orig_rvaddr - ufi->entry->start) + ufi->entry->offset;
        access_type = flt->access_type & MASK(ufi->entry);
        advice = ufi->entry->advice;

        /* Locked: maps(read), amap(if there), uobj */
        KASSERT(rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);

        /* Upgrade to a write lock if needed. */
        error = uvm_fault_lower_upgrade(ufi, flt, amap, uobj, NULL);
        if (error != 0) {
                return error;
        }
        uvmfault_unlockall(ufi, amap, NULL);

        /* update rusage counters */
        curlwp->l_ru.ru_majflt++;

        /* Locked: uobj(write) */
        KASSERT(rw_write_held(uobj->vmobjlock));

        cpu_count(CPU_COUNT_FLTGET, 1);
        gotpages = 1;
        pg = NULL;
        error = uobj->pgops->pgo_get(uobj, uoff, &pg, &gotpages,
            0, access_type, advice, PGO_SYNCIO);
        /* locked: pg(if no error) */

        /*
         * recover from I/O
         */

        if (error) {
                if (error == EAGAIN) {
                        UVMHIST_LOG(maphist,
                            "  pgo_get says TRY AGAIN!",0,0,0,0);
                        kpause("fltagain2", false, hz/2, NULL);
                        return ERESTART;
                }

#if 0
                KASSERT(error != ERESTART);
#else
                /* XXXUEBS don't re-fault? */
                if (error == ERESTART)
                        error = EIO;
#endif

                UVMHIST_LOG(maphist, "<- pgo_get failed (code %jd)",
                    error, 0,0,0);
                return error;
        }

        /*
         * re-verify the state of the world by first trying to relock
         * the maps.  always relock the object.
         */

        locked = uvmfault_relock(ufi);
        if (locked && amap)
                amap_lock(amap, flt->upper_lock_type);

        /* might be changed */
        uobj = pg->uobject;

        rw_enter(uobj->vmobjlock, flt->lower_lock_type);
        KASSERT((pg->flags & PG_BUSY) != 0);
        KASSERT(flt->lower_lock_type == RW_WRITER);

        uvm_pagelock(pg);
        uvm_pageactivate(pg);
        uvm_pageunlock(pg);

        /* locked(locked): maps(read), amap(if !null), uobj, pg */
        /* locked(!locked): uobj, pg */

        /*
         * verify that the page has not be released and re-verify
         * that amap slot is still free.   if there is a problem,
         * we unlock and clean up.
         */

        if ((pg->flags & PG_RELEASED) != 0 ||
            (locked && amap && amap_lookup(&ufi->entry->aref,
              ufi->orig_rvaddr - ufi->entry->start))) {
                if (locked)
                        uvmfault_unlockall(ufi, amap, NULL);
                locked = false;
        }

        /*
         * unbusy/release the page.
         */

        if ((pg->flags & PG_RELEASED) == 0) {
                pg->flags &= ~PG_BUSY;
                uvm_pagelock(pg);
                uvm_pagewakeup(pg);
                uvm_pageunlock(pg);
                UVM_PAGE_OWN(pg, NULL);
        } else {
                cpu_count(CPU_COUNT_FLTPGRELE, 1);
                uvm_pagefree(pg);
        }

        /*
         * didn't get the lock?   retry.
         */

        if (locked == false) {
                UVMHIST_LOG(maphist,
                    "  wasn't able to relock after fault: retry",
                    0,0,0,0);
                rw_exit(uobj->vmobjlock);
                return ERESTART;
        }

        /*
         * we have the data in pg.  we are holding object lock (so the page
         * can't be released on us).
         */

        /* locked: maps(read), amap(if !null), uobj */

        *ruobj = uobj;
        *ruobjpage = pg;
        return 0;
}

/*
 * uvm_fault_lower_direct: fault lower center page
 *
 *      1. adjust flt->enter_prot.
 *      2. if page is loaned, resolve.
 */

int
uvm_fault_lower_direct(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_page *uobjpage)
{
        struct vm_page *pg;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /*
         * we are not promoting.   if the mapping is COW ensure that we
         * don't give more access than we should (e.g. when doing a read
         * fault on a COPYONWRITE mapping we want to map the COW page in
         * R/O even though the entry protection could be R/W).
         *
         * set "pg" to the page we want to map in (uobjpage, usually)
         */

        cpu_count(CPU_COUNT_FLT_OBJ, 1);
        if (UVM_ET_ISCOPYONWRITE(ufi->entry) ||
            UVM_OBJ_NEEDS_WRITEFAULT(uobjpage->uobject))
                flt->enter_prot &= ~VM_PROT_WRITE;
        pg = uobjpage;          /* map in the actual object */

        KASSERT(uobjpage != PGO_DONTCARE);

        /*
         * we are faulting directly on the page.   be careful
         * about writing to loaned pages...
         */

        if (uobjpage->loan_count) {
                uvm_fault_lower_direct_loan(ufi, flt, uobj, &pg, &uobjpage);
        }
        KASSERT(pg == uobjpage);
        KASSERT((pg->flags & PG_BUSY) == 0);
        return uvm_fault_lower_enter(ufi, flt, uobj, NULL, pg);
}

/*
 * uvm_fault_lower_direct_loan: resolve loaned page.
 *
 *      1. if not cow'ing, adjust flt->enter_prot.
 *      2. if cow'ing, break loan.
 */

static int
uvm_fault_lower_direct_loan(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_page **rpg,
        struct vm_page **ruobjpage)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        struct vm_page *pg;
        struct vm_page *uobjpage = *ruobjpage;
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        if (!flt->cow_now) {
                /* read fault: cap the protection at readonly */
                /* cap! */
                flt->enter_prot = flt->enter_prot & ~VM_PROT_WRITE;
        } else {
                /*
                 * write fault: must break the loan here.  to do this
                 * we need a write lock on the object.
                 */

                error = uvm_fault_lower_upgrade(ufi, flt, amap, uobj, uobjpage);
                if (error != 0) {
                        return error;
                }
                KASSERT(rw_write_held(uobj->vmobjlock));

                pg = uvm_loanbreak(uobjpage);
                if (pg == NULL) {

                        uvmfault_unlockall(ufi, amap, uobj);
                        UVMHIST_LOG(maphist,
                          "  out of RAM breaking loan, waiting",
                          0,0,0,0);
                        cpu_count(CPU_COUNT_FLTNORAM, 1);
                        uvm_wait("flt_noram4");
                        return ERESTART;
                }
                *rpg = pg;
                *ruobjpage = pg;

                /*
                 * drop ownership of page while still holding object lock,
                 * which won't be dropped until the page is entered.
                 */

                uvm_pagelock(pg);
                uvm_pagewakeup(pg);
                uvm_pageunlock(pg);
                pg->flags &= ~PG_BUSY;
                UVM_PAGE_OWN(pg, NULL);
        }
        return 0;
}

/*
 * uvm_fault_lower_promote: promote lower page.
 *
 *      1. call uvmfault_promote.
 *      2. fill in data.
 *      3. if not ZFOD, dispose old page.
 */

int
uvm_fault_lower_promote(
        struct uvm_faultinfo *ufi, struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_page *uobjpage)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        struct vm_anon *anon;
        struct vm_page *pg;
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        KASSERT(amap != NULL);

        /* promoting requires a write lock. */
        error = uvm_fault_upper_upgrade(ufi, flt, amap, uobj);
        if (error != 0) {
                return error;
        }
        KASSERT(rw_write_held(amap->am_lock));
        KASSERT(uobj == NULL ||
            rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);

        /*
         * If we are going to promote the data to an anon we
         * allocate a blank anon here and plug it into our amap.
         */
        error = uvmfault_promote(ufi, NULL, uobjpage, &anon, &flt->anon_spare);
        switch (error) {
        case 0:
                break;
        case ERESTART:
                return ERESTART;
        default:
                return error;
        }

        pg = anon->an_page;

        /*
         * Fill in the data.
         */

        if (uobjpage != PGO_DONTCARE) {
                cpu_count(CPU_COUNT_FLT_PRCOPY, 1);

                /*
                 * promote to shared amap?  make sure all sharing
                 * procs see it
                 */

                if ((amap_flags(amap) & AMAP_SHARED) != 0) {
                        pmap_page_protect(uobjpage, VM_PROT_NONE);
                        /*
                         * XXX: PAGE MIGHT BE WIRED!
                         */
                }

                UVMHIST_LOG(maphist,
                    "  promote uobjpage %#jx to anon/page %#jx/%#jx",
                    (uintptr_t)uobjpage, (uintptr_t)anon, (uintptr_t)pg, 0);

        } else {
                cpu_count(CPU_COUNT_FLT_PRZERO, 1);

                /*
                 * Page is zero'd and marked dirty by
                 * uvmfault_promote().
                 */

                UVMHIST_LOG(maphist,"  zero fill anon/page %#jx/%#jx",
                    (uintptr_t)anon, (uintptr_t)pg, 0, 0);
        }

        return uvm_fault_lower_enter(ufi, flt, uobj, anon, pg);
}

/*
 * uvm_fault_lower_enter: enter h/w mapping of lower page or anon page promoted
 * from the lower page.
 */

int
uvm_fault_lower_enter(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        struct uvm_object *uobj,
        struct vm_anon *anon, struct vm_page *pg)
{
        struct vm_amap * const amap = ufi->entry->aref.ar_amap;
        const bool readonly = uvm_pagereadonly_p(pg);
        int error;
        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        /*
         * Locked:
         *
         *      maps(read), amap(if !null), uobj(if !null),
         *      anon(if !null), pg(if anon), unlock_uobj(if !null)
         *
         * anon must be write locked (promotion).  uobj can be either.
         *
         * Note: pg is either the uobjpage or the new page in the new anon.
         */

        KASSERT(amap == NULL ||
            rw_lock_op(amap->am_lock) == flt->upper_lock_type);
        KASSERT(uobj == NULL ||
            rw_lock_op(uobj->vmobjlock) == flt->lower_lock_type);
        KASSERT(anon == NULL || anon->an_lock == amap->am_lock);

        /*
         * note that pg can't be PG_RELEASED or PG_BUSY since we did
         * not drop the object lock since the last time we checked.
         */

        KASSERT((pg->flags & PG_RELEASED) == 0);
        KASSERT((pg->flags & PG_BUSY) == 0);

        /*
         * all resources are present.   we can now map it in and free our
         * resources.
         */

        UVMHIST_LOG(maphist,
            "  MAPPING: case2: pm=%#jx, va=%#jx, pg=%#jx, promote=%jd",
            (uintptr_t)ufi->orig_map->pmap, ufi->orig_rvaddr,
            (uintptr_t)pg, flt->promote);
        KASSERTMSG((flt->access_type & VM_PROT_WRITE) == 0 || !readonly,
            "promote=%u cow_now=%u access_type=%x enter_prot=%x cow=%u "
            "entry=%p map=%p orig_rvaddr=%p pg=%p",
            flt->promote, flt->cow_now, flt->access_type, flt->enter_prot,
            UVM_ET_ISCOPYONWRITE(ufi->entry), ufi->entry, ufi->orig_map,
            (void *)ufi->orig_rvaddr, pg);
        KASSERT((flt->access_type & VM_PROT_WRITE) == 0 || !readonly);
        if (pmap_enter(ufi->orig_map->pmap, ufi->orig_rvaddr,
            VM_PAGE_TO_PHYS(pg),
            readonly ? flt->enter_prot & ~VM_PROT_WRITE : flt->enter_prot,
            flt->access_type | PMAP_CANFAIL |
            (flt->wire_mapping ? PMAP_WIRED : 0)) != 0) {

                /*
                 * No need to undo what we did; we can simply think of
                 * this as the pmap throwing away the mapping information.
                 *
                 * We do, however, have to go through the ReFault path,
                 * as the map may change while we're asleep.
                 */

                /*
                 * ensure that the page is queued in the case that
                 * we just promoted the page.
                 */

                if (anon != NULL) {
                        uvm_pagelock(pg);
                        uvm_pageenqueue(pg);
                        uvm_pagewakeup(pg);
                        uvm_pageunlock(pg);
                }

                uvmfault_unlockall(ufi, amap, uobj);
                if (!uvm_reclaimable()) {
                        UVMHIST_LOG(maphist,
                            "<- failed.  out of VM",0,0,0,0);
                        /* XXX instrumentation */
                        error = ENOMEM;
                        return error;
                }
                /* XXX instrumentation */
                uvm_wait("flt_pmfail2");
                return ERESTART;
        }

        uvm_fault_lower_done(ufi, flt, uobj, pg);
        pmap_update(ufi->orig_map->pmap);
        uvmfault_unlockall(ufi, amap, uobj);

        UVMHIST_LOG(maphist, "<- done (SUCCESS!)",0,0,0,0);
        return 0;
}

/*
 * uvm_fault_lower_done: queue lower center page.
 */

void
uvm_fault_lower_done(
        struct uvm_faultinfo *ufi, const struct uvm_faultctx *flt,
        struct uvm_object *uobj, struct vm_page *pg)
{

        UVMHIST_FUNC(__func__); UVMHIST_CALLED(maphist);

        if (flt->wire_paging) {
                uvm_pagelock(pg);
                uvm_pagewire(pg);
                uvm_pageunlock(pg);
                if (pg->flags & PG_AOBJ) {

                        /*
                         * since the now-wired page cannot be paged out,
                         * release its swap resources for others to use.
                         * since an aobj page with no swap cannot be clean,
                         * mark it dirty now.
                         *
                         * use pg->uobject here.  if the page is from a
                         * tmpfs vnode, the pages are backed by its UAO and
                         * not the vnode.
                         */

                        KASSERT(uobj != NULL);
                        KASSERT(uobj->vmobjlock == pg->uobject->vmobjlock);
                        uvm_pagemarkdirty(pg, UVM_PAGE_STATUS_DIRTY);
                        uao_dropswap(pg->uobject, pg->offset >> PAGE_SHIFT);
                }
        } else if (uvmpdpol_pageactivate_p(pg)) {
                /*
                 * avoid re-activating the page unless needed,
                 * to avoid false sharing on multiprocessor.
                 */

                uvm_pagelock(pg);
                uvm_pageactivate(pg);
                uvm_pageunlock(pg);
        }
}


/*
 * uvm_fault_wire: wire down a range of virtual addresses in a map.
 *
 * => map may be read-locked by caller, but MUST NOT be write-locked.
 * => if map is read-locked, any operations which may cause map to
 *      be write-locked in uvm_fault() must be taken care of by
 *      the caller.  See uvm_map_pageable().
 */

int
uvm_fault_wire(struct vm_map *map, vaddr_t start, vaddr_t end,
    vm_prot_t access_type, int maxprot)
{
        vaddr_t va;
        int error;

        /*
         * now fault it in a page at a time.   if the fault fails then we have
         * to undo what we have done.   note that in uvm_fault VM_PROT_NONE
         * is replaced with the max protection if fault_type is VM_FAULT_WIRE.
         */

        /*
         * XXX work around overflowing a vaddr_t.  this prevents us from
         * wiring the last page in the address space, though.
         */
        if (start > end) {
                return EFAULT;
        }

        for (va = start; va < end; va += PAGE_SIZE) {
                error = uvm_fault_internal(map, va, access_type,
                    (maxprot ? UVM_FAULT_MAXPROT : 0) | UVM_FAULT_WIRE);
                if (error) {
                        if (va != start) {
                                uvm_fault_unwire(map, start, va);
                        }
                        return error;
                }
        }
        return 0;
}

/*
 * uvm_fault_unwire(): unwire range of virtual space.
 */

void
uvm_fault_unwire(struct vm_map *map, vaddr_t start, vaddr_t end)
{
        vm_map_lock_read(map);
        uvm_fault_unwire_locked(map, start, end);
        vm_map_unlock_read(map);
}

/*
 * uvm_fault_unwire_locked(): the guts of uvm_fault_unwire().
 *
 * => map must be at least read-locked.
 */

void
uvm_fault_unwire_locked(struct vm_map *map, vaddr_t start, vaddr_t end)
{
        struct vm_map_entry *entry, *oentry;
        pmap_t pmap = vm_map_pmap(map);
        vaddr_t va;
        paddr_t pa;
        struct vm_page *pg;

        /*
         * we assume that the area we are unwiring has actually been wired
         * in the first place.   this means that we should be able to extract
         * the PAs from the pmap.   we also lock out the page daemon so that
         * we can call uvm_pageunwire.
         */

        /*
         * find the beginning map entry for the region.
         */

        KASSERT(start >= vm_map_min(map));
        KASSERT(end <= vm_map_max(map));
        if (uvm_map_lookup_entry(map, start, &entry) == false)
                panic("uvm_fault_unwire_locked: address not in map");

        oentry = NULL;
        for (va = start; va < end; va += PAGE_SIZE) {

                /*
                 * find the map entry for the current address.
                 */

                KASSERT(va >= entry->start);
                while (va >= entry->end) {
                        KASSERT(entry->next != &map->header);
                        KASSERT(entry->next->start <= entry->end);
                        entry = entry->next;
                }

                /*
                 * lock it.
                 */

                if (entry != oentry) {
                        if (oentry != NULL) {
                                uvm_map_unlock_entry(oentry);
                        }
                        uvm_map_lock_entry(entry, RW_WRITER);
                        oentry = entry;
                }

                /*
                 * if the entry is no longer wired, tell the pmap.
                 */

                if (!pmap_extract(pmap, va, &pa))
                        continue;

                if (VM_MAPENT_ISWIRED(entry) == 0)
                        pmap_unwire(pmap, va);

                pg = PHYS_TO_VM_PAGE(pa);
                if (pg) {
                        uvm_pagelock(pg);
                        uvm_pageunwire(pg);
                        uvm_pageunlock(pg);
                }
        }

        if (oentry != NULL) {
                uvm_map_unlock_entry(entry);
        }
}