FreeBSD/Linux Kernel Cross Reference
sys/uvm/uvm_fault.c

     /*      $NetBSD: uvm_fault.c,v 1.116 2006/12/01 19:15:22 yamt 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.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Charles D. Cranor and
     *      Washington University.
     * 4. The name of the author may not be used to endorse or promote products
     *    derived from this software without specific prior written permission.
     *
     * 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 1.116 2006/12/01 19:15:22 yamt Exp $");
    
    #include "opt_uvmhist.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/proc.h>
    #include <sys/malloc.h>
    #include <sys/mman.h>
    #include <sys/user.h>
    
    #include <uvm/uvm.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 top 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:
    *     - 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...).
    *
    * given that we are not currently multiprocessor or multithreaded we might
    * as well choose alternative 2 now.   maybe alternative 3 would be useful
    * in the future.    XXX keep in mind for future consideration//rechecking.
    */
   
   /*
    * 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[] = {
           { MADV_NORMAL, 3, 4 },
           { MADV_RANDOM, 0, 0 },
           { MADV_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;
                   simple_lock(&anons[lcv]->an_lock);
                   pg = anons[lcv]->an_page;
                   if (pg && (pg->flags & PG_BUSY) == 0 && pg->loan_count == 0) {
                           uvm_lock_pageq();
                           if (pg->wire_count == 0) {
                                   pmap_clear_reference(pg);
                                   uvm_pagedeactivate(pg);
                           }
                           uvm_unlock_pageq();
                   }
                   simple_unlock(&anons[lcv]->an_lock);
           }
   }
   
   /*
    * 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.
    *
    * => maps, amap, and anon locked by caller.
    * => if we fail (result != 0) we unlock everything.
    * => if we are successful, we return with everything still locked.
    * => we don't 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, we 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)
   {
           boolean_t we_own;       /* we own anon's page? */
           boolean_t locked;       /* did we relock? */
           struct vm_page *pg;
           int error;
           UVMHIST_FUNC("uvmfault_anonget"); UVMHIST_CALLED(maphist);
   
           LOCK_ASSERT(simple_lock_held(&anon->an_lock));
   
           error = 0;
           uvmexp.fltanget++;
           /* bump rusage counters */
           if (anon->an_page)
                   curproc->p_stats->p_ru.ru_minflt++;
           else
                   curproc->p_stats->p_ru.ru_majflt++;
   
           /*
            * loop until we get it, or fail.
            */
   
           for (;;) {
                   we_own = FALSE;         /* TRUE if we set PG_BUSY on a page */
                   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_lockpage() to ensure
                    * the real owner of the page has been identified and locked.
                    */
   
                   if (pg && pg->loan_count)
                           pg = uvm_anon_lockloanpg(anon);
   
                   /*
                    * page there?   make sure it is not busy/released.
                    */
   
                   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);
                           }
                           pg->flags |= PG_WANTED;
                           uvmexp.fltpgwait++;
   
                           /*
                            * the last unlock must be an atomic unlock+wait on
                            * the owner of page
                            */
   
                           if (pg->uobject) {      /* owner is uobject ? */
                                   uvmfault_unlockall(ufi, amap, NULL, anon);
                                   UVMHIST_LOG(maphist, " unlock+wait on uobj",0,
                                       0,0,0);
                                   UVM_UNLOCK_AND_WAIT(pg,
                                       &pg->uobject->vmobjlock,
                                       FALSE, "anonget1",0);
                           } else {
                                   /* anon owns page */
                                   uvmfault_unlockall(ufi, amap, NULL, NULL);
                                   UVMHIST_LOG(maphist, " unlock+wait on anon",0,
                                       0,0,0);
                                   UVM_UNLOCK_AND_WAIT(pg,&anon->an_lock,0,
                                       "anonget2",0);
                           }
                   } else {
   #if defined(VMSWAP)
   
                           /*
                            * no page, we must try and bring it in.
                            */
   
                           pg = uvm_pagealloc(NULL, 0, anon, 0);
                           if (pg == NULL) {               /* out of RAM.  */
                                   uvmfault_unlockall(ufi, amap, NULL, anon);
                                   uvmexp.fltnoram++;
                                   UVMHIST_LOG(maphist, "  noram -- UVM_WAIT",0,
                                       0,0,0);
                                   if (!uvm_reclaimable()) {
                                           return ENOMEM;
                                   }
                                   uvm_wait("flt_noram1");
                           } else {
                                   /* we set the PG_BUSY bit */
                                   we_own = TRUE;
                                   uvmfault_unlockall(ufi, amap, NULL, anon);
   
                                   /*
                                    * we are passing a PG_BUSY+PG_FAKE+PG_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.
                                    */
                                   uvmexp.pageins++;
                                   error = uvm_swap_get(pg, anon->an_swslot,
                                       PGO_SYNCIO);
   
                                   /*
                                    * we clean up after the i/o below in the
                                    * "we_own" case
                                    */
                           }
   #else /* defined(VMSWAP) */
                           panic("%s: no page", __func__);
   #endif /* defined(VMSWAP) */
                   }
   
                   /*
                    * now relock and try again
                    */
   
                   locked = uvmfault_relock(ufi);
                   if (locked && amap != NULL) {
                           amap_lock(amap);
                   }
                   if (locked || we_own)
                           simple_lock(&anon->an_lock);
   
                   /*
                    * 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 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) {
   #if defined(VMSWAP)
                           if (pg->flags & PG_WANTED) {
                                   wakeup(pg);
                           }
                           if (error) {
   
                                   /*
                                    * remove the swap slot from the anon
                                    * and mark the anon as having no real slot.
                                    * don't 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
                                    * can't be mapped and thus no need to
                                    * pmap_page_protect it...
                                    */
   
                                   uvm_lock_pageq();
                                   uvm_pagefree(pg);
                                   uvm_unlock_pageq();
   
                                   if (locked)
                                           uvmfault_unlockall(ufi, amap, NULL,
                                               anon);
                                   else
                                           simple_unlock(&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 unlocked amap.
                                    */
   
                                   if (locked)
                                           uvmfault_unlockall(ufi, amap, 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've successfully read the page, activate it.
                            */
   
                           uvm_lock_pageq();
                           uvm_pageactivate(pg);
                           uvm_unlock_pageq();
                           pg->flags &= ~(PG_WANTED|PG_BUSY|PG_FAKE);
                           UVM_PAGE_OWN(pg, NULL);
                           if (!locked)
                                   simple_unlock(&anon->an_lock);
   #else /* defined(VMSWAP) */
                           panic("%s: we_own", __func__);
   #endif /* defined(VMSWAP) */
                   }
   
                   /*
                    * we were not able to relock.   restart fault.
                    */
   
                   if (!locked) {
                           UVMHIST_LOG(maphist, "<- REFAULT", 0,0,0,0);
                           return (ERESTART);
                   }
   
                   /*
                    * verify 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, anon);
                           UVMHIST_LOG(maphist, "<- REFAULT", 0,0,0,0);
                           return (ERESTART);
                   }
   
                   /*
                    * try it again!
                    */
   
                   uvmexp.fltanretry++;
                   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.
    */
   
   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;
           } else {
                   /* ZFOD */
                   opg = NULL;
           }
           if (opg != NULL) {
                   uobj = opg->uobject;
           } else {
                   uobj = NULL;
           }
   
           KASSERT(amap != NULL);
           KASSERT(uobjpage != NULL);
           KASSERT(uobjpage == PGO_DONTCARE || (uobjpage->flags & PG_BUSY) != 0);
           LOCK_ASSERT(simple_lock_held(&amap->am_l));
           LOCK_ASSERT(oanon == NULL || simple_lock_held(&oanon->an_lock));
           LOCK_ASSERT(uobj == NULL || simple_lock_held(&uobj->vmobjlock));
           LOCK_ASSERT(*spare == NULL || !simple_lock_held(&(*spare)->an_lock));
   
           if (*spare != NULL) {
                   anon = *spare;
                   *spare = NULL;
                   simple_lock(&anon->an_lock);
           } else if (ufi->map != kernel_map) {
                   anon = uvm_analloc();
           } else {
                   UVMHIST_LOG(maphist, "kernel_map, unlock and retry", 0,0,0,0);
   
                   /*
                    * we can't allocate anons with kernel_map locked.
                    */
   
                   uvm_page_unbusy(&uobjpage, 1);
                   uvmfault_unlockall(ufi, amap, uobj, oanon);
   
                   *spare = uvm_analloc();
                   if (*spare == NULL) {
                           goto nomem;
                   }
                   simple_unlock(&(*spare)->an_lock);
                   error = ERESTART;
                   goto done;
           }
           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.
                    */
   
                   pg = uvm_pagealloc(NULL, 0, anon,
                       (opg == NULL) ? UVM_PGA_ZERO : 0);
           } else {
                   pg = NULL;
           }
   
           /*
            * out of memory resources?
            */
   
           if (pg == NULL) {
                   /* save anon for the next try. */
                   if (anon != NULL) {
                           simple_unlock(&anon->an_lock);
                           *spare = anon;
                   }
   
                   /* unlock and fail ... */
                   uvm_page_unbusy(&uobjpage, 1);
                   uvmfault_unlockall(ufi, amap, uobj, oanon);
   nomem:
                   if (!uvm_reclaimable()) {
                           UVMHIST_LOG(maphist, "out of VM", 0,0,0,0);
                           uvmexp.fltnoanon++;
                           error = ENOMEM;
                           goto done;
                   }
   
                   UVMHIST_LOG(maphist, "out of RAM, waiting for more", 0,0,0,0);
                   uvmexp.fltnoram++;
                   uvm_wait("flt_noram5");
                   error = ERESTART;
                   goto done;
           }
   
           /* copy page [pg now dirty] */
           if (opg) {
                   uvm_pagecopy(opg, pg);
           }
   
           amap_add(&ufi->entry->aref, ufi->orig_rvaddr - ufi->entry->start, anon,
               oanon != NULL);
   
           *nanon = anon;
           error = 0;
   done:
           return error;
   }
   
   
   /*
    *   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 recusive, 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
   #define UVM_FAULT_WIREMAX 2
   
   int
   uvm_fault_internal(struct vm_map *orig_map, vaddr_t vaddr,
       vm_prot_t access_type, int fault_flag)
   {
           struct uvm_faultinfo ufi;
           vm_prot_t enter_prot, check_prot;
           boolean_t wired, narrow, promote, locked, shadowed, wire_fault, cow_now;
           int npages, nback, nforw, centeridx, error, lcv, gotpages;
           vaddr_t startva, currva;
           voff_t uoff;
           struct vm_amap *amap;
           struct uvm_object *uobj;
           struct vm_anon *anons_store[UVM_MAXRANGE], **anons, *anon, *oanon;
           struct vm_anon *anon_spare;
           struct vm_page *pages[UVM_MAXRANGE], *pg, *uobjpage;
           UVMHIST_FUNC("uvm_fault"); UVMHIST_CALLED(maphist);
   
           UVMHIST_LOG(maphist, "(map=0x%x, vaddr=0x%x, at=%d, ff=%d)",
                 orig_map, vaddr, access_type, fault_flag);
   
           anon = anon_spare = NULL;
           pg = NULL;
   
           uvmexp.faults++;        /* XXX: locking? */
   
           /*
            * 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 */
           wire_fault = (fault_flag > 0);
           if (wire_fault)
                   narrow = TRUE;          /* don't look for neighborhood
                                            * pages on wire */
           else
                   narrow = FALSE;         /* normal fault */
   
           /*
            * "goto ReFault" means restart the page fault from ground zero.
            */
   ReFault:
   
           /*
            * lookup and lock the maps
            */
   
           if (uvmfault_lookup(&ufi, FALSE) == FALSE) {
                   UVMHIST_LOG(maphist, "<- no mapping @ 0x%x", vaddr, 0,0,0);
                   error = EFAULT;
                   goto done;
           }
           /* 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 = 0x%lx\n", (u_long) ufi.orig_rvaddr);
                   panic("uvm_fault: (ufi.map->flags & VM_MAP_PAGEABLE) == 0");
           }
   #endif
   
           /*
            * check protection
            */
   
           check_prot = fault_flag == UVM_FAULT_WIREMAX ?
               ufi.entry->max_protection : ufi.entry->protection;
           if ((check_prot & access_type) != access_type) {
                   UVMHIST_LOG(maphist,
                       "<- protection failure (prot=0x%x, access=0x%x)",
                       ufi.entry->protection, access_type, 0, 0);
                   uvmfault_unlockmaps(&ufi, FALSE);
                   error = EACCES;
                   goto done;
           }
   
           /*
            * "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.
            */
   
           enter_prot = ufi.entry->protection;
           wired = VM_MAPENT_ISWIRED(ufi.entry) || wire_fault;
           if (wired) {
                   access_type = enter_prot; /* full access for wired */
                   cow_now = (check_prot & VM_PROT_WRITE) != 0;
           } else {
                   cow_now = (access_type & VM_PROT_WRITE) != 0;
           }
   
           /*
            * 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 (cow_now || (ufi.entry->object.uvm_obj == NULL)) {
                           KASSERT(fault_flag != UVM_FAULT_WIREMAX);
                           /* need to clear */
                           UVMHIST_LOG(maphist,
                               "  need to clear needs_copy and refault",0,0,0,0);
                           uvmfault_unlockmaps(&ufi, FALSE);
                           uvmfault_amapcopy(&ufi);
                           uvmexp.fltamcopy++;
                           goto ReFault;
   
                   } else {
   
                           /*
                            * ensure that we pmap_enter page R/O since
                            * needs_copy is still true
                            */
   
                           enter_prot &= ~VM_PROT_WRITE;
                   }
           }
   
           /*
            * identify the players
            */
   
           amap = ufi.entry->aref.ar_amap;         /* top layer */
           uobj = ufi.entry->object.uvm_obj;       /* bottom 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);
                   error = EFAULT;
                   goto done;
           }
   
           /*
            * 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 (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);
                   startva = ufi.orig_rvaddr - (nback << PAGE_SHIFT);
                   nforw = MIN(uvmadvice[ufi.entry->advice].nforw,
                               ((ufi.entry->end - ufi.orig_rvaddr) >>
                                PAGE_SHIFT) - 1);
                   /*
                    * note: "-1" because we don't want to count the
                    * faulting page as forw
                    */
                   npages = nback + nforw + 1;
                   centeridx = nback;
   
                   narrow = TRUE;  /* ensure only once per-fault */
   
           } else {
   
                   /* narrow fault! */
                   nback = nforw = 0;
                   startva = ufi.orig_rvaddr;
                   npages = 1;
                   centeridx = 0;
   
           }
   
           /* locked: maps(read) */
           UVMHIST_LOG(maphist, "  narrow=%d, back=%d, forw=%d, startva=0x%x",
                       narrow, nback, nforw, startva);
           UVMHIST_LOG(maphist, "  entry=0x%x, amap=0x%x, obj=0x%x", ufi.entry,
                       amap, uobj, 0);
   
           /*
            * if we've got an amap, lock it and extract current anons.
            */
   
           if (amap) {
                   amap_lock(amap);
                   anons = anons_store;
                   amap_lookups(&ufi.entry->aref, startva - ufi.entry->start,
                       anons, npages);
           } else {
                   anons = NULL;   /* to be safe */
           }
   
           /* locked: maps(read), amap(if there) */
           LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
   
           /*
            * 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(anons, nback);
   
                   /* flush object? */
                   if (uobj) {
                           uoff = (startva - ufi.entry->start) + ufi.entry->offset;
                           simple_lock(&uobj->vmobjlock);
                           (void) (uobj->pgops->pgo_put)(uobj, uoff, uoff +
                                       (nback << PAGE_SHIFT), PGO_DEACTIVATE);
                   }
   
                   /* now forget about the backpages */
                   if (amap)
                           anons += nback;
                   startva += (nback << PAGE_SHIFT);
                   npages -= nback;
                   nback = centeridx = 0;
           }
   
           /* locked: maps(read), amap(if there) */
           LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
   
           /*
            * 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 = startva;
           shadowed = FALSE;
           for (lcv = 0 ; lcv < npages ; lcv++, currva += PAGE_SIZE) {
   
                   /*
                    * dont play with VAs that are already mapped
                    * except for center)
                    */
                   if (lcv != centeridx &&
                       pmap_extract(ufi.orig_map->pmap, currva, NULL)) {
                           pages[lcv] = PGO_DONTCARE;
                           continue;
                   }
   
                   /*
                    * 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.   re-activate it.
                    */
   
                   pages[lcv] = PGO_DONTCARE;
                   if (lcv == centeridx) {         /* save center for later! */
                           shadowed = TRUE;
                           continue;
                   }
                   anon = anons[lcv];
                   simple_lock(&anon->an_lock);
                   /* ignore loaned pages */
                   if (anon->an_page && anon->an_page->loan_count == 0 &&
                       (anon->an_page->flags & PG_BUSY) == 0) {
                           uvm_lock_pageq();
                           uvm_pageenqueue(anon->an_page);
                           uvm_unlock_pageq();
                           UVMHIST_LOG(maphist,
                               "  MAPPING: n anon: pm=0x%x, va=0x%x, pg=0x%x",
                               ufi.orig_map->pmap, currva, anon->an_page, 0);
                           uvmexp.fltnamap++;
   
                           /*
                            * Since this 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(anon->an_page),
                               (anon->an_ref > 1) ? (enter_prot & ~VM_PROT_WRITE) :
                               enter_prot,
                               PMAP_CANFAIL |
                                (VM_MAPENT_ISWIRED(ufi.entry) ? PMAP_WIRED : 0));
                   }
                   simple_unlock(&anon->an_lock);
                   pmap_update(ufi.orig_map->pmap);
           }
   
           /* locked: maps(read), amap(if there) */
           LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
          /* (shadowed == TRUE) if there is an anon at the faulting address */
          UVMHIST_LOG(maphist, "  shadowed=%d, will_get=%d", shadowed,
              (uobj && shadowed == FALSE),0,0);
  
          /*
           * note that if we are really short of RAM we could sleep in the above
           * call to pmap_enter with everything locked.   bad?
           *
           * XXX Actually, that is bad; pmap_enter() should just fail in that
           * XXX case.  --thorpej
           */
  
          /*
           * if the desired page is not shadowed by the amap and we have a
           * backing object, then we check to see if the backing object would
           * prefer to handle the fault itself (rather than letting us do it
           * with the usual pgo_get hook).  the backing object signals this by
           * providing a pgo_fault routine.
           */
  
          if (uobj && shadowed == FALSE && uobj->pgops->pgo_fault != NULL) {
                  simple_lock(&uobj->vmobjlock);
  
                  /* locked: maps(read), amap (if there), uobj */
                  error = uobj->pgops->pgo_fault(&ufi, startva, pages, npages,
                      centeridx, access_type, PGO_LOCKED|PGO_SYNCIO);
  
                  /* locked: nothing, pgo_fault has unlocked everything */
  
                  if (error == ERESTART)
                          goto ReFault;           /* try again! */
                  /*
                   * object fault routine responsible for pmap_update().
                   */
                  goto done;
          }
  
          /*
           * 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 && shadowed == FALSE) {
                  simple_lock(&uobj->vmobjlock);
  
                  /* locked (!shadowed): maps(read), amap (if there), uobj */
                  /*
                   * the following call to pgo_get does _not_ change locking state
                   */
  
                  uvmexp.fltlget++;
                  gotpages = npages;
                  (void) uobj->pgops->pgo_get(uobj, ufi.entry->offset +
                                  (startva - ufi.entry->start),
                                  pages, &gotpages, centeridx,
                                  access_type & MASK(ufi.entry),
                                  ufi.entry->advice, PGO_LOCKED);
  
                  /*
                   * check for pages to map, if we got any
                   */
  
                  uobjpage = NULL;
  
                  if (gotpages) {
                          currva = startva;
                          for (lcv = 0; lcv < npages;
                               lcv++, currva += PAGE_SIZE) {
                                  struct vm_page *curpg;
                                  boolean_t readonly;
  
                                  curpg = pages[lcv];
                                  if (curpg == NULL || curpg == PGO_DONTCARE) {
                                          continue;
                                  }
                                  KASSERT(curpg->uobject == uobj);
  
                                  /*
                                   * if center page is resident and not
                                   * PG_BUSY|PG_RELEASED then pgo_get
                                   * made it PG_BUSY for us and gave
                                   * us a handle to it.   remember this
                                   * page as "uobjpage." (for later use).
                                   */
  
                                  if (lcv == centeridx) {
                                          uobjpage = curpg;
                                          UVMHIST_LOG(maphist, "  got uobjpage "
                                              "(0x%x) with locked get",
                                              uobjpage, 0,0,0);
                                          continue;
                                  }
  
                                  /*
                                   * 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.
                                   */
  
                                  uvm_lock_pageq();
                                  uvm_pageenqueue(curpg);
                                  uvm_unlock_pageq();
                                  UVMHIST_LOG(maphist,
                                    "  MAPPING: n obj: pm=0x%x, va=0x%x, pg=0x%x",
                                    ufi.orig_map->pmap, currva, curpg, 0);
                                  uvmexp.fltnomap++;
  
                                  /*
                                   * 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.
                                   */
                                  KASSERT((curpg->flags & PG_PAGEOUT) == 0);
                                  KASSERT((curpg->flags & PG_RELEASED) == 0);
                                  KASSERT(!UVM_OBJ_IS_CLEAN(curpg->uobject) ||
                                      (curpg->flags & PG_CLEAN) != 0);
                                  readonly = (curpg->flags & PG_RDONLY)
                                      || (curpg->loan_count > 0)
                                      || UVM_OBJ_NEEDS_WRITEFAULT(curpg->uobject);
  
                                  (void) pmap_enter(ufi.orig_map->pmap, currva,
                                      VM_PAGE_TO_PHYS(curpg),
                                      readonly ?
                                      enter_prot & ~VM_PROT_WRITE :
                                      enter_prot & MASK(ufi.entry),
                                      PMAP_CANFAIL |
                                       (wired ? PMAP_WIRED : 0));
  
                                  /*
                                   * NOTE: page can't be PG_WANTED or PG_RELEASED
                                   * because we've held the lock the whole time
                                   * we've had the handle.
                                   */
                                  KASSERT((curpg->flags & PG_WANTED) == 0);
                                  KASSERT((curpg->flags & PG_RELEASED) == 0);
  
                                  curpg->flags &= ~(PG_BUSY);
                                  UVM_PAGE_OWN(curpg, NULL);
                          }
                          pmap_update(ufi.orig_map->pmap);
                  }
          } else {
                  uobjpage = NULL;
          }
  
          /* locked (shadowed): maps(read), amap */
          /* locked (!shadowed): maps(read), amap(if there),
                   uobj(if !null), uobjpage(if !null) */
          if (shadowed) {
                  LOCK_ASSERT(simple_lock_held(&amap->am_l));
          } else {
                  LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
                  LOCK_ASSERT(uobj == NULL || simple_lock_held(&uobj->vmobjlock));
                  KASSERT(uobjpage == NULL || (uobjpage->flags & PG_BUSY) != 0);
          }
  
          /*
           * 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 top (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.
           */
  
          /*
           * there are four possible cases we must address: 1A, 1B, 2A, and 2B
           */
  
          /*
           * redirect case 2: if we are not shadowed, go to case 2.
           */
  
          if (shadowed == FALSE)
                  goto Case2;
  
          /* locked: maps(read), amap */
  
          /*
           * handle case 1: fault on an anon in our amap
           */
  
          anon = anons[centeridx];
          UVMHIST_LOG(maphist, "  case 1 fault: anon=0x%x", anon, 0,0,0);
          simple_lock(&anon->an_lock);
  
          /* locked: maps(read), amap, anon */
          LOCK_ASSERT(simple_lock_held(&amap->am_l));
          LOCK_ASSERT(simple_lock_held(&anon->an_lock));
  
          /*
           * 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.
           */
  
          error = uvmfault_anonget(&ufi, amap, anon);
          switch (error) {
          case 0:
                  break;
  
          case ERESTART:
                  goto ReFault;
  
          case EAGAIN:
                  tsleep(&lbolt, PVM, "fltagain1", 0);
                  goto ReFault;
  
          default:
                  goto done;
          }
  
          /*
           * 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) */
          LOCK_ASSERT(simple_lock_held(&amap->am_l));
          LOCK_ASSERT(simple_lock_held(&anon->an_lock));
          LOCK_ASSERT(uobj == NULL || simple_lock_held(&uobj->vmobjlock));
  
          /*
           * special handling for loaned pages
           */
  
          if (anon->an_page->loan_count) {
  
                  if (!cow_now) {
  
                          /*
                           * for read faults on loaned pages we just cap the
                           * protection at read-only.
                           */
  
                          enter_prot = 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) {
  
                                  /* get new un-owned replacement page */
                                  pg = uvm_pagealloc(NULL, 0, NULL, 0);
                                  if (pg == NULL) {
                                          uvmfault_unlockall(&ufi, amap, uobj,
                                              anon);
                                          uvm_wait("flt_noram2");
                                          goto ReFault;
                                  }
  
                                  /*
                                   * copy data, kill loan, and drop uobj lock
                                   * (if any)
                                   */
                                  /* copy old -> new */
                                  uvm_pagecopy(anon->an_page, pg);
  
                                  /* force reload */
                                  pmap_page_protect(anon->an_page, VM_PROT_NONE);
                                  uvm_lock_pageq();         /* KILL loan */
  
                                  anon->an_page->uanon = NULL;
                                  /* in case we owned */
                                  anon->an_page->pqflags &= ~PQ_ANON;
  
                                  if (uobj) {
                                          /* if we were receiver of loan */
                                          anon->an_page->loan_count--;
                                  } else {
                                          /*
                                           * we were the lender (A->K); need
                                           * to remove the page from pageq's.
                                           */
                                          uvm_pagedequeue(anon->an_page);
                                  }
  
                                  if (uobj) {
                                          simple_unlock(&uobj->vmobjlock);
                                          uobj = NULL;
                                  }
  
                                  /* install new page in anon */
                                  anon->an_page = pg;
                                  pg->uanon = anon;
                                  pg->pqflags |= PQ_ANON;
  
                                  uvm_pageactivate(pg);
                                  uvm_unlock_pageq();
  
                                  pg->flags &= ~(PG_BUSY|PG_FAKE);
                                  UVM_PAGE_OWN(pg, NULL);
  
                                  /* done! */
                          }     /* ref == 1 */
                  }       /* write fault */
          }         /* loan count */
  
          /*
           * 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 (cow_now && anon->an_ref > 1) {
  
                  UVMHIST_LOG(maphist, "  case 1B: COW fault",0,0,0,0);
                  uvmexp.flt_acow++;
                  oanon = anon;           /* oanon = old, locked anon */
  
                  error = uvmfault_promote(&ufi, oanon, PGO_DONTCARE,
                      &anon, &anon_spare);
                  switch (error) {
                  case 0:
                          break;
                  case ERESTART:
                          goto ReFault;
                  default:
                          goto done;
                  }
  
                  pg = anon->an_page;
                  uvm_lock_pageq();
                  uvm_pageactivate(pg);
                  uvm_unlock_pageq();
                  pg->flags &= ~(PG_BUSY|PG_FAKE);
                  UVM_PAGE_OWN(pg, NULL);
  
                  /* deref: can not drop to zero here by defn! */
                  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.
                   */
  
          } else {
  
                  uvmexp.flt_anon++;
                  oanon = anon;           /* old, locked anon is same as anon */
                  pg = anon->an_page;
                  if (anon->an_ref > 1)     /* disallow writes to ref > 1 anons */
                          enter_prot = enter_prot & ~VM_PROT_WRITE;
  
          }
  
          /* locked: maps(read), amap, oanon, anon (if different from oanon) */
          LOCK_ASSERT(simple_lock_held(&amap->am_l));
          LOCK_ASSERT(simple_lock_held(&anon->an_lock));
          LOCK_ASSERT(simple_lock_held(&oanon->an_lock));
  
          /*
           * now map the page in.
           */
  
          UVMHIST_LOG(maphist, "  MAPPING: anon: pm=0x%x, va=0x%x, pg=0x%x",
              ufi.orig_map->pmap, ufi.orig_rvaddr, pg, 0);
          if (pmap_enter(ufi.orig_map->pmap, ufi.orig_rvaddr, VM_PAGE_TO_PHYS(pg),
              enter_prot, access_type | PMAP_CANFAIL | (wired ? 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.
                   */
  
                  if (anon != oanon)
                          simple_unlock(&anon->an_lock);
                  uvmfault_unlockall(&ufi, amap, uobj, oanon);
                  if (!uvm_reclaimable()) {
                          UVMHIST_LOG(maphist,
                              "<- failed.  out of VM",0,0,0,0);
                          /* XXX instrumentation */
                          error = ENOMEM;
                          goto done;
                  }
                  /* XXX instrumentation */
                  uvm_wait("flt_pmfail1");
                  goto ReFault;
          }
  
          /*
           * ... update the page queues.
           */
  
          uvm_lock_pageq();
          if (wire_fault) {
                  uvm_pagewire(pg);
  
                  /*
                   * since the now-wired page cannot be paged out,
                   * release its swap resources for others to use.
                   * since an anon with no swap cannot be PG_CLEAN,
                   * clear its clean flag now.
                   */
  
                  pg->flags &= ~(PG_CLEAN);
                  uvm_anon_dropswap(anon);
          } else {
                  uvm_pageactivate(pg);
          }
          uvm_unlock_pageq();
  
          /*
           * done case 1!  finish up by unlocking everything and returning success
           */
  
          if (anon != oanon)
                  simple_unlock(&anon->an_lock);
          uvmfault_unlockall(&ufi, amap, uobj, oanon);
          pmap_update(ufi.orig_map->pmap);
          error = 0;
          goto done;
  
  Case2:
          /*
           * handle case 2: faulting on backing object or zero fill
           */
  
          /*
           * locked:
           * maps(read), amap(if there), uobj(if !null), uobjpage(if !null)
           */
          LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
          LOCK_ASSERT(uobj == NULL || simple_lock_held(&uobj->vmobjlock));
          LOCK_ASSERT(uobjpage == NULL || (uobjpage->flags & PG_BUSY) != 0);
  
          /*
           * 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;
                  promote = TRUE;         /* always need anon here */
          } else {
                  KASSERT(uobjpage != PGO_DONTCARE);
                  promote = cow_now && UVM_ET_ISCOPYONWRITE(ufi.entry);
          }
          UVMHIST_LOG(maphist, "  case 2 fault: promote=%d, zfill=%d",
              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 */
                  curproc->p_stats->p_ru.ru_minflt++;
          } else {
                  /* update rusage counters */
                  curproc->p_stats->p_ru.ru_majflt++;
  
                  /* locked: maps(read), amap(if there), uobj */
                  uvmfault_unlockall(&ufi, amap, NULL, NULL);
                  /* locked: uobj */
  
                  uvmexp.fltget++;
                  gotpages = 1;
                  uoff = (ufi.orig_rvaddr - ufi.entry->start) + ufi.entry->offset;
                  error = uobj->pgops->pgo_get(uobj, uoff, &uobjpage, &gotpages,
                      0, access_type & MASK(ufi.entry), ufi.entry->advice,
                      PGO_SYNCIO);
                  /* locked: uobjpage(if no error) */
                  LOCK_ASSERT(error != 0 || (uobjpage->flags & PG_BUSY) != 0);
  
                  /*
                   * recover from I/O
                   */
  
                  if (error) {
                          if (error == EAGAIN) {
                                  UVMHIST_LOG(maphist,
                                      "  pgo_get says TRY AGAIN!",0,0,0,0);
                                  tsleep(&lbolt, PVM, "fltagain2", 0);
                                  goto ReFault;
                          }
  
                          UVMHIST_LOG(maphist, "<- pgo_get failed (code %d)",
                              error, 0,0,0);
                          goto done;
                  }
  
                  /* locked: uobjpage */
  
                  uvm_lock_pageq();
                  uvm_pageactivate(uobjpage);
                  uvm_unlock_pageq();
  
                  /*
                   * 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);
                  uobj = uobjpage->uobject;
                  simple_lock(&uobj->vmobjlock);
  
                  /* locked(locked): maps(read), amap(if !null), uobj, uobjpage */
                  /* locked(!locked): uobj, uobjpage */
  
                  /*
                   * 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 ((uobjpage->flags & PG_RELEASED) != 0 ||
                      (locked && amap &&
                      amap_lookup(&ufi.entry->aref,
                        ufi.orig_rvaddr - ufi.entry->start))) {
                          if (locked)
                                  uvmfault_unlockall(&ufi, amap, NULL, NULL);
                          locked = FALSE;
                  }
  
                  /*
                   * didn't get the lock?   release the page and retry.
                   */
  
                  if (locked == FALSE) {
                          UVMHIST_LOG(maphist,
                              "  wasn't able to relock after fault: retry",
                              0,0,0,0);
                          if (uobjpage->flags & PG_WANTED)
                                  wakeup(uobjpage);
                          if (uobjpage->flags & PG_RELEASED) {
                                  uvmexp.fltpgrele++;
                                  uvm_pagefree(uobjpage);
                                  goto ReFault;
                          }
                          uobjpage->flags &= ~(PG_BUSY|PG_WANTED);
                          UVM_PAGE_OWN(uobjpage, NULL);
                          simple_unlock(&uobj->vmobjlock);
                          goto ReFault;
                  }
  
                  /*
                   * we have the data in uobjpage which is busy and
                   * not released.  we are holding object lock (so the page
                   * can't be released on us).
                   */
  
                  /* locked: maps(read), amap(if !null), uobj, uobjpage */
          }
  
          /*
           * locked:
           * maps(read), amap(if !null), uobj(if !null), uobjpage(if uobj)
           */
          LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
          LOCK_ASSERT(uobj == NULL || simple_lock_held(&uobj->vmobjlock));
          LOCK_ASSERT(uobj == NULL || (uobjpage->flags & PG_BUSY) != 0);
  
          /*
           * 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 PG_WANTED (handle later)
           */
  
          KASSERT(uobj == NULL || uobj == uobjpage->uobject);
          KASSERT(uobj == NULL || !UVM_OBJ_IS_CLEAN(uobjpage->uobject) ||
              (uobjpage->flags & PG_CLEAN) != 0);
          if (promote == FALSE) {
  
                  /*
                   * 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)
                   */
  
                  /* no anon in this case. */
                  anon = NULL;
  
                  uvmexp.flt_obj++;
                  if (UVM_ET_ISCOPYONWRITE(ufi.entry) ||
                      UVM_OBJ_NEEDS_WRITEFAULT(uobjpage->uobject))
                          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) {
                          if (!cow_now) {
                                  /* read fault: cap the protection at readonly */
                                  /* cap! */
                                  enter_prot = enter_prot & ~VM_PROT_WRITE;
                          } else {
                                  /* write fault: must break the loan here */
  
                                  pg = uvm_loanbreak(uobjpage);
                                  if (pg == NULL) {
  
                                          /*
                                           * drop ownership of page, it can't
                                           * be released
                                           */
  
                                          if (uobjpage->flags & PG_WANTED)
                                                  wakeup(uobjpage);
                                          uobjpage->flags &= ~(PG_BUSY|PG_WANTED);
                                          UVM_PAGE_OWN(uobjpage, NULL);
  
                                          uvmfault_unlockall(&ufi, amap, uobj,
                                            NULL);
                                          UVMHIST_LOG(maphist,
                                            "  out of RAM breaking loan, waiting",
                                            0,0,0,0);
                                          uvmexp.fltnoram++;
                                          uvm_wait("flt_noram4");
                                          goto ReFault;
                                  }
                                  uobjpage = pg;
                          }
                  }
          } else {
  
                  /*
                   * if we are going to promote the data to an anon we
                   * allocate a blank anon here and plug it into our amap.
                   */
  #if DIAGNOSTIC
                  if (amap == NULL)
                          panic("uvm_fault: want to promote data, but no anon");
  #endif
                  error = uvmfault_promote(&ufi, NULL, uobjpage,
                      &anon, &anon_spare);
                  switch (error) {
                  case 0:
                          break;
                  case ERESTART:
                          goto ReFault;
                  default:
                          goto done;
                  }
  
                  pg = anon->an_page;
  
                  /*
                   * fill in the data
                   */
  
                  if (uobjpage != PGO_DONTCARE) {
                          uvmexp.flt_prcopy++;
  
                          /*
                           * 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!
                                   */
                          }
  
                          /*
                           * dispose of uobjpage.  it can't be PG_RELEASED
                           * since we still hold the object lock.
                           * drop handle to uobj as well.
                           */
  
                          if (uobjpage->flags & PG_WANTED)
                                  /* still have the obj lock */
                                  wakeup(uobjpage);
                          uobjpage->flags &= ~(PG_BUSY|PG_WANTED);
                          UVM_PAGE_OWN(uobjpage, NULL);
                          simple_unlock(&uobj->vmobjlock);
                          uobj = NULL;
  
                          UVMHIST_LOG(maphist,
                              "  promote uobjpage 0x%x to anon/page 0x%x/0x%x",
                              uobjpage, anon, pg, 0);
  
                  } else {
                          uvmexp.flt_przero++;
  
                          /*
                           * Page is zero'd and marked dirty by
                           * uvmfault_promote().
                           */
  
                          UVMHIST_LOG(maphist,"  zero fill anon/page 0x%x/0%x",
                              anon, pg, 0, 0);
                  }
          }
  
          /*
           * locked:
           * maps(read), amap(if !null), uobj(if !null), uobjpage(if uobj),
           *   anon(if !null), pg(if anon)
           *
           * note: pg is either the uobjpage or the new page in the new anon
           */
          LOCK_ASSERT(amap == NULL || simple_lock_held(&amap->am_l));
          LOCK_ASSERT(uobj == NULL || simple_lock_held(&uobj->vmobjlock));
          LOCK_ASSERT(uobj == NULL || (uobjpage->flags & PG_BUSY) != 0);
          LOCK_ASSERT(anon == NULL || simple_lock_held(&anon->an_lock));
          LOCK_ASSERT((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=0x%x, va=0x%x, pg=0x%x, promote=%d",
              ufi.orig_map->pmap, ufi.orig_rvaddr, pg, promote);
          KASSERT((access_type & VM_PROT_WRITE) == 0 ||
                  (pg->flags & PG_RDONLY) == 0);
          if (pmap_enter(ufi.orig_map->pmap, ufi.orig_rvaddr, VM_PAGE_TO_PHYS(pg),
              pg->flags & PG_RDONLY ? enter_prot & ~VM_PROT_WRITE : enter_prot,
              access_type | PMAP_CANFAIL | (wired ? 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.
                   */
  
                  if (pg->flags & PG_WANTED)
                          wakeup(pg);
  
                  /*
                   * note that pg can't be PG_RELEASED since we did not drop
                   * the object lock since the last time we checked.
                   */
                  KASSERT((pg->flags & PG_RELEASED) == 0);
  
                  pg->flags &= ~(PG_BUSY|PG_FAKE|PG_WANTED);
                  UVM_PAGE_OWN(pg, NULL);
                  uvmfault_unlockall(&ufi, amap, uobj, anon);
                  if (!uvm_reclaimable()) {
                          UVMHIST_LOG(maphist,
                              "<- failed.  out of VM",0,0,0,0);
                          /* XXX instrumentation */
                          error = ENOMEM;
                          goto done;
                  }
                  /* XXX instrumentation */
                  uvm_wait("flt_pmfail2");
                  goto ReFault;
          }
  
          uvm_lock_pageq();
          if (wire_fault) {
                  uvm_pagewire(pg);
                  if (pg->pqflags & PQ_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 PG_CLEAN,
                           * clear its clean flag now.
                           */
  
                          KASSERT(uobj != NULL);
                          pg->flags &= ~(PG_CLEAN);
                          uao_dropswap(uobj, pg->offset >> PAGE_SHIFT);
                  }
          } else {
                  uvm_pageactivate(pg);
          }
          uvm_unlock_pageq();
          if (pg->flags & PG_WANTED)
                  wakeup(pg);
  
          /*
           * note that pg can't be PG_RELEASED since we did not drop the object
           * lock since the last time we checked.
           */
          KASSERT((pg->flags & PG_RELEASED) == 0);
  
          pg->flags &= ~(PG_BUSY|PG_FAKE|PG_WANTED);
          UVM_PAGE_OWN(pg, NULL);
          uvmfault_unlockall(&ufi, amap, uobj, anon);
          pmap_update(ufi.orig_map->pmap);
          UVMHIST_LOG(maphist, "<- done (SUCCESS!)",0,0,0,0);
          error = 0;
  done:
          if (anon_spare != NULL) {
                  anon_spare->an_ref--;
                  uvm_anfree(anon_spare);
          }
          return error;
  }
  
  
  /*
   * 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 wiremax)
  {
          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,
                                  wiremax ? UVM_FAULT_WIREMAX : 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;
          pmap_t pmap = vm_map_pmap(map);
          vaddr_t va;
          paddr_t pa;
          struct vm_page *pg;
  
          KASSERT((map->flags & VM_MAP_INTRSAFE) == 0);
  
          /*
           * 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.
           */
  
          uvm_lock_pageq();
  
          /*
           * find the beginning map entry for the region.
           */
  
          KASSERT(start >= vm_map_min(map) && end <= vm_map_max(map));
          if (uvm_map_lookup_entry(map, start, &entry) == FALSE)
                  panic("uvm_fault_unwire_locked: address not in map");
  
          for (va = start; va < end; va += PAGE_SIZE) {
                  if (pmap_extract(pmap, va, &pa) == FALSE)
                          continue;
  
                  /*
                   * find the map entry for the current address.
                   */
  
                  KASSERT(va >= entry->start);
                  while (va >= entry->end) {
                          KASSERT(entry->next != &map->header &&
                                  entry->next->start <= entry->end);
                          entry = entry->next;
                  }
  
                  /*
                   * if the entry is no longer wired, tell the pmap.
                   */
  
                  if (VM_MAPENT_ISWIRED(entry) == 0)
                          pmap_unwire(pmap, va);
  
                  pg = PHYS_TO_VM_PAGE(pa);
                  if (pg)
                          uvm_pageunwire(pg);
          }
  
          uvm_unlock_pageq();
  }

Cache object: b92a06ec3a4fe451db89dc4e0cb71572