xref: /src/sys/uvm/uvm_fault.c

/*	$Id: uvm_fault.c,v 1.1 1998/02/05 06:25:10 mrg Exp $	*/

/*
 * XXXCDC: "ROUGH DRAFT" QUALITY UVM PRE-RELEASE FILE!
 *	   >>>USE AT YOUR OWN RISK, WORK IS NOT FINISHED<<<
 */
/*
 *
 * 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.
 */

/*
 * uvm_fault.c: fault handler
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/kernel.h>
#include <sys/mount.h>
#include <sys/proc.h>
#include <sys/malloc.h>
#include <sys/mman.h>

#include <vm/vm.h>
#include <vm/vm_page.h>
#include <vm/vm_kern.h>

#include <sys/syscallargs.h>

#include <uvm/uvm.h>

UVMHIST_DECL(maphist);

/*
 *
 * 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 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
 */

static void uvmfault_amapcopy __P((struct uvm_faultinfo *));
static __inline void uvmfault_anonflush __P((struct vm_anon **, int));

/*
 * 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(anons, n)

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]->u.an_page;
    if (pg && (pg->flags & PG_BUSY) == 0 && pg->loan_count == 0) {
      uvm_lock_pageq();
      if (pg->wire_count == 0) {
        pmap_page_protect(PMAP_PGARG(pg), VM_PROT_NONE);
        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(ufi)

struct uvm_faultinfo *ufi;

{

  /*
   * while we haven't done the job
   */

  while (1) {

    /*
     * 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, M_NOWAIT, TRUE, ufi->rvaddr,
		ufi->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 != VM_PAGER_OK) 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(ufi, amap, anon)

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 result;
  UVMHIST_FUNC("uvmfault_anonget"); UVMHIST_CALLED(maphist);

  result = 0;		/* XXX shut up gcc */
  uvmexp.fltanget++;	/* XXXDCD should this go here or below? */

  /*
   * loop until we get it, or fail.
   */

  while (1) {

    we_own = FALSE;		/* TRUE if we set PG_BUSY on a page */
    pg = anon->u.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|PG_RELEASED)) == 0) {
        UVMHIST_LOG(maphist, "<- OK",0,0,0,0);
	return(VM_PAGER_OK);
      }
      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);
      }
      /* ready to relock and try again */

    } else {

      /*
       * no page, we must try and bring it in.
       */
      pg = uvm_pagealloc(NULL, 0, anon);

      if (pg == NULL) {		/* out of RAM.  */

	uvmfault_unlockall(ufi, amap, NULL, anon);
	uvmexp.fltnoram++;
        UVMHIST_LOG(maphist, "  noram -- UVM_WAIT",0,0,0,0);
	uvm_wait("flt_noram1");
	/* ready to relock and try again */

      } else {

	we_own = TRUE;			/* we set the PG_BUSY bit */
	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.
	 */
	result = uvm_swap_get(pg, anon->an_swslot, PGO_SYNCIO);
	/* XXXMRG: we need a counter here! */

	/*
	 * we clean up after the i/o below in the "we_own" case
	 */
	/* ready to relock and try again */
      }

    }

    /*
     * now relock and try again
     */

    locked = uvmfault_relock(ufi);
    if (locked) {
      simple_lock(&amap->am_l);
    }
    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 (pg->flags & PG_WANTED) {
	thread_wakeup(pg);		/* still holding object lock */
      }
      pg->flags &= ~(PG_WANTED|PG_BUSY|PG_FAKE);	/* un-busy! */
      UVM_PAGE_OWN(pg, NULL);

      /*
       * if we were RELEASED during I/O, then our anon is no longer
       * part of an amap.   we need to free the anon and try again.
       */
      if (pg->flags & PG_RELEASED) {
        pmap_page_protect(PMAP_PGARG(pg), VM_PROT_NONE); /* to be safe */
	uvm_anfree(anon);	/* frees page for us */
	if (locked)
	  uvmfault_unlockall(ufi, amap, NULL, NULL);
	uvmexp.fltpgrele++;
        UVMHIST_LOG(maphist, "<- REFAULT", 0,0,0,0);
	return(VM_PAGER_REFAULT);		/* refault! */
      }

      if (result != VM_PAGER_OK) {
#ifdef DIAGNOSTIC
	if (result == VM_PAGER_PEND)
	  panic("uvmfault_anonget: got PENDING for non-async I/O");
#endif
	/* remove page from anon */
	anon->u.an_page = NULL;
	/*
	 * 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(VM_PAGER_ERROR);
      }

      /* must be OK, clear modify (already PG_CLEAN) and activate */
      pmap_clear_modify(PMAP_PGARG(pg));
      uvm_lock_pageq();
      uvm_pageactivate(pg);
      uvm_unlock_pageq();
      if (!locked)
	simple_unlock(&anon->an_lock);
    }

    /*
     * we were not able to relock.   restart fault.
     */

    if (!locked) {
      UVMHIST_LOG(maphist, "<- REFAULT", 0,0,0,0);
      return(VM_PAGER_REFAULT);
    }

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

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

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

    /*
     * try it again!
     */

    uvmexp.fltanretry++;
    continue;
  } /* while (1) */

  /*NOTREACHED*/
}

/*
 *   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.
 */

int uvm_fault(orig_map, vaddr, fault_type, access_type)

vm_map_t orig_map;
vm_offset_t vaddr;
vm_fault_t fault_type;
vm_prot_t access_type;

{
  struct uvm_faultinfo ufi;
  vm_prot_t enter_prot;
  boolean_t wired, narrow, promote, locked, shadowed;
  int npages, nback, nforw, centeridx, result, lcv, gotpages;
  vm_offset_t orig_startva, startva, objaddr, currva, pa, offset;
  struct vm_amap *amap;
  struct uvm_object *uobj;
  struct vm_anon *anons_store[UVM_MAXRANGE], **anons, *anon, *oanon;
  struct vm_page *pages[UVM_MAXRANGE], *pg, *uobjpage;
  UVMHIST_FUNC("uvm_fault"); UVMHIST_CALLED(maphist);

  UVMHIST_LOG(maphist, "(map=0x%x, vaddr=0x%x, ft=%d, at=%d)",
	      orig_map, vaddr, fault_type, access_type);

  anon = NULL; /* XXX: shut up gcc */

  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 */
  if (fault_type == VM_FAULT_WIRE)
    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);
    return(KERN_INVALID_ADDRESS);
  }
  /* locked: maps(read) */

  /*
   * check protection
   */

  if ((ufi.entry->protection & 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);
    return(KERN_PROTECTION_FAILURE);
  }

  /*
   * "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 = (ufi.entry->wired_count != 0) || (fault_type == VM_FAULT_WIRE);
  if (wired)
    access_type = enter_prot; /* full access for wired */

  /*
   * 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 ((access_type & VM_PROT_WRITE) || (ufi.entry->object.uvm_obj == NULL)) {

      /* 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 = 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);
    return(KERN_INVALID_ADDRESS);
  }

  /*
   * 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) */
#ifdef DIAGNOSTIC
    if (uvmadvice[ufi.entry->advice].advice != ufi.entry->advice)
      panic("fault: advice mismatch!");
#endif
    nback = min(uvmadvice[ufi.entry->advice].nback,
		(ufi.rvaddr - ufi.entry->start) / PAGE_SIZE);
    startva = ufi.rvaddr - (nback * PAGE_SIZE);
    orig_startva = ufi.orig_rvaddr - (nback * PAGE_SIZE);
    nforw = min(uvmadvice[ufi.entry->advice].nforw,
		((ufi.entry->end - ufi.rvaddr) / PAGE_SIZE) - 1);
    /* note: "-1" because we don't want to count the faulting page as forw */
    npages = nback + nforw + 1;
    centeridx = nback;

    narrow = FALSE;	/* ensure only once per-fault */

  } else {

    /* narrow fault! */
    nback = nforw = 0;
    startva = ufi.rvaddr;
    orig_startva = ufi.orig_rvaddr;
    npages = 1;
    centeridx = 0;

  }

  /* locked: maps(read) */
  UVMHIST_LOG(maphist, "  narrow=%d, back=%d, forw=%d, orig_startva=0x%x",
	narrow, nback, nforw, orig_startva);
  UVMHIST_LOG(maphist, "  entry=0x%x, amap=0x%x, obj=0x%x", ufi.entry,
	amap, uobj, 0);
#if 0
/* TEST TEST TEST ONLY ... DELETE  */
{/*XXXCDC:DBG*/
vm_map_t map = ufi.map;
UVMHIST_LOG(maphist, "  startva=0x%x, entrystart=0x%x", startva,
	ufi.entry->start,0,0); /*XXXCDC: tmp */
uvm_map_print(map, 1);
}/*XXXCDC:DBG*/
#endif

  /*
   * if we've got an amap, lock it and extract current anons.
   */

  if (amap) {
    simple_lock(&amap->am_l);
    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) */

  /*
   * 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) {

    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) {
      objaddr = (startva - ufi.entry->start) + ufi.entry->offset;
      simple_lock(&uobj->vmobjlock);
      (void) uobj->pgops->pgo_flush(uobj, objaddr, objaddr +
				    (nback * PAGE_SIZE), PGO_DEACTIVATE);
      simple_unlock(&uobj->vmobjlock);
    }

    /* now forget about the backpages */
    if (amap)
      anons += nback;
    startva = startva + (nback * PAGE_SIZE);
    orig_startva = orig_startva + (nback * PAGE_SIZE);
    npages -= nback;
    nback = centeridx = 0;
  }

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

  /*
   * 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 = orig_startva;
  shadowed = FALSE;
  for (lcv = 0 ; lcv < npages ; lcv++, currva += PAGE_SIZE) {

    /*
     * dont play with VAs that are already mapped (except for center)
     * XXX: return value of pmap_extract disallows PA 0
     */
    if (lcv != centeridx) {
      pa = pmap_extract(ufi.orig_map->pmap, currva);
      if (pa != 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->u.an_page && anon->u.an_page->loan_count == 0 &&
	(anon->u.an_page->flags & (PG_RELEASED|PG_BUSY)) == 0) {
      uvm_lock_pageq();
      uvm_pageactivate(anon->u.an_page);	/* reactivate */
      uvm_unlock_pageq();
      UVMHIST_LOG(maphist, "  MAPPING: n anon: pm=0x%x, va=0x%x, pg=0x%x",
	ufi.orig_map->pmap, currva, anon->u.an_page, 0);
      uvmexp.fltnamap++;
      pmap_enter(ufi.orig_map->pmap, currva, VM_PAGE_TO_PHYS(anon->u.an_page),
		 (anon->an_ref > 1) ? VM_PROT_READ : enter_prot,
		 (ufi.entry->wired_count != 0));
    }
    simple_unlock(&anon->an_lock);
  }

  /* locked: maps(read), amap(if there) */
  /* (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?
   * XXXCDC: this is fixed in PMAP_NEW (no sleep alloc's in pmap)
   */

  /*
   * 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.
   *
   * note: pgo_fault can obtain the correct VA for pmap_enter by using:
   *    real_va = [ ufi->orig_rvaddr + (startva - ufi->rvaddr)]
   */

  if (uobj && shadowed == FALSE && uobj->pgops->pgo_fault != NULL) {

    simple_lock(&uobj->vmobjlock);

    /* locked: maps(read), amap (if there), uobj */
    result = uobj->pgops->pgo_fault(&ufi, startva, pages, npages,
				    centeridx, fault_type, access_type,
				    PGO_LOCKED);
    /* locked: nothing, pgo_fault has unlocked everything */

    if (result == VM_PAGER_OK)
      return(KERN_SUCCESS);           /* pgo_fault did pmap enter */
    else if (result == VM_PAGER_REFAULT)
      goto ReFault;                   /* try again! */
    else
      return(KERN_PROTECTION_FAILURE);
  }

  /*
   * 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).
   *
   * ("get" has the option of doing a pmap_enter for us)
   */

  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;
    result = uobj->pgops->pgo_get(uobj, ufi.entry->offset +
				(startva - ufi.entry->start),
				pages, &gotpages, centeridx,
				UVM_ET_ISCOPYONWRITE(ufi.entry) ?
				VM_PROT_READ : access_type,
				ufi.entry->advice, PGO_LOCKED);

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

    uobjpage = NULL;

    if (gotpages) {
      currva = orig_startva;
      for (lcv = 0 ; lcv < npages ; lcv++, currva += PAGE_SIZE) {

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

#ifdef DIAGNOSTIC
        /*
         * pager sanity check: pgo_get with PGO_LOCKED should never
         * return a released page to us.
         */
        if (pages[lcv]->flags & PG_RELEASED)
	  panic("uvm_fault: pgo_get PGO_LOCKED gave us a RELEASED page");
#endif

        /*
         * 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 = pages[lcv];
	  UVMHIST_LOG(maphist, "  got uobjpage (0x%x) with locked get",
		  uobjpage, 0,0,0);
	  continue;
        }

        /*
         * note: calling pgo_get with locked data structures returns us
         * pages which are neither busy nor released, so we don't need to
         * check for this.   we can just directly enter the page (after
         * moving it to the head of the active queue [useful?]).
         */

        uvm_lock_pageq();
        uvm_pageactivate(pages[lcv]);	/* reactivate */
        uvm_unlock_pageq();
        UVMHIST_LOG(maphist, "  MAPPING: n obj: pm=0x%x, va=0x%x, pg=0x%x",
	  ufi.orig_map->pmap, currva, pages[lcv], 0);
        uvmexp.fltnomap++;
        pmap_enter(ufi.orig_map->pmap, currva, VM_PAGE_TO_PHYS(pages[lcv]),
	   UVM_ET_ISCOPYONWRITE(ufi.entry) ?  VM_PROT_READ : enter_prot, wired);

        /*
         * NOTE: page can't be PG_WANTED or PG_RELEASED because we've held
         * the lock the whole time we've had the handle.
         */
        pages[lcv]->flags &= ~(PG_BUSY);		/* un-busy! */
        UVM_PAGE_OWN(pages[lcv], NULL);

        /* done! */
      }	/* for "lcv" loop */
    }   /* "gotpages" != 0 */

    /* note: object still _locked_ */
  } else {

    uobjpage = NULL;

  }

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

  /*
   * 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 and tmpwired it.
   */

  /*
   * 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 */

  /*
   * 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 for us.   if it is OK, 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.
   */

  result = uvmfault_anonget(&ufi, amap, anon);

  if (result == VM_PAGER_REFAULT)
    goto ReFault;

  if (result == VM_PAGER_AGAIN) {
    tsleep((caddr_t)&lbolt, PVM, "fltagain1", 0);
    goto ReFault;
  }

  if (result != VM_PAGER_OK)
    return(KERN_PROTECTION_FAILURE);		/* XXX??? */

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

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

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

  /*
   * special handling for loaned pages
   */
  if (anon->u.an_page->loan_count) {

    if ((access_type & VM_PROT_WRITE) == 0) {

      /*
       * 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.
       */

      if (anon->an_ref == 1) {		/* >1 case is already ok */

	/* get new un-owned replacement page */
	pg = uvm_pagealloc(NULL, 0, NULL);
	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) */
	uvm_pagecopy(anon->u.an_page, pg);		  /* copy old -> new */
	/* force reload */
	pmap_page_protect(PMAP_PGARG(anon->u.an_page), VM_PROT_NONE);
	uvm_lock_pageq();				  /* KILL loan */
        if (uobj)
	  anon->u.an_page->loan_count--;		/* if we were loaning */
	anon->u.an_page->uanon = NULL;
	anon->u.an_page->pqflags &= ~PQ_ANON;		/* in case we owned */
	uvm_unlock_pageq();
	if (uobj) {
	  simple_unlock(&uobj->vmobjlock);
	  uobj = NULL;
	}

	/* install new page in anon */
	anon->u.an_page = pg;
	pg->uanon = anon;
	pg->pqflags |= PQ_ANON;
        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 ((access_type & VM_PROT_WRITE) != 0 && anon->an_ref > 1) {

    UVMHIST_LOG(maphist, "  case 1B: COW fault",0,0,0,0);
    uvmexp.flt_acow++;
    oanon = anon;		/* oanon = old, locked anon */
    anon = uvm_analloc();
    if (anon)
      pg = uvm_pagealloc(NULL, 0, anon);
#if defined(sparc)
    else
      pg = NULL; /* XXX: shut up gcc unused var warning on sparc */
#endif

    /* check for out of RAM */
    if (anon == NULL || pg == NULL) {
      if (anon)
	uvm_anfree(anon);
      uvmfault_unlockall(&ufi, amap, uobj, oanon);
      if (anon == NULL) {
	UVMHIST_LOG(maphist, "<- failed.  out of VM",0,0,0,0);
	uvmexp.fltnoanon++;
	return(KERN_RESOURCE_SHORTAGE); /* XXX: OUT OF VM, ??? */
      }
      uvmexp.fltnoram++;
      uvm_wait("flt_noram3");	/* out of RAM, wait for more */
      goto ReFault;
    }

    /* got all resources, replace anon with nanon */

    uvm_pagecopy(oanon->u.an_page, pg);	/* pg now !PG_CLEAN */
    pg->flags &= ~(PG_BUSY|PG_FAKE);	/* un-busy! new page */
    UVM_PAGE_OWN(pg, NULL);
    amap_add(&ufi.entry->aref, ufi.rvaddr - ufi.entry->start, anon, 1);
    oanon->an_ref--;   /* deref: can not drop to zero here by defn! */

    /*
     * note: oanon still locked.   anon is _not_ locked, but we have
     * the sole references to in from amap which _is_ locked.   thus,
     * no one can get at it until we are done with it.
     */

  } else {

    uvmexp.flt_anon++;
    oanon = anon;		/* old, locked anon is same as anon */
    pg = anon->u.an_page;
    if (anon->an_ref > 1)     /* never allow writes to ref > 1 anons */
      enter_prot = enter_prot & ~VM_PROT_WRITE;

  }

  /* locked: maps(read), amap, anon */

  /*
   * now map the page in ...
   * XXX: old fault unlocks object before pmap_enter.  this seems
   * suspect since some other thread could blast the page out from
   * under us between the unlock and the pmap_enter.
   */

  UVMHIST_LOG(maphist, "  MAPPING: anon: pm=0x%x, va=0x%x, pg=0x%x",
    ufi.orig_map->pmap, ufi.orig_rvaddr, pg, 0);
  pmap_enter(ufi.orig_map->pmap, ufi.orig_rvaddr, VM_PAGE_TO_PHYS(pg),
	     enter_prot, wired);

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

  uvm_lock_pageq();

  if (fault_type == VM_FAULT_WIRE) {

      uvm_pagewire(pg, FALSE);

  } else {

    /* tmpwire page to remove from q's if we didn't just allocate it */
    if (anon == oanon)
      uvm_pagewire(pg, TRUE);

    /* activate it */
    uvm_pageactivate(pg);

  }

  uvm_unlock_pageq();

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

  uvmfault_unlockall(&ufi, amap, uobj, oanon);
  return(KERN_SUCCESS);


Case2:
  /*
   * handle case 2: faulting on backing object or zero fill
   */

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

  /*
   * 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 {
    /* assert(uobjpage != PGO_DONTCARE) */
    promote = (access_type & VM_PROT_WRITE) && UVM_ET_ISCOPYONWRITE(ufi.entry);
  }
  UVMHIST_LOG(maphist, "  case 2 fault: promote=%d, zfill=%d",
	promote, (uobj == NULL), 0,0);

  /*
   * 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 == NULL) {

    /* locked: maps(read), amap(if there), uobj */
    uvmfault_unlockall(&ufi, amap, NULL, NULL);
    /* locked: uobj */

    uvmexp.fltget++;
    gotpages = 1;
    result = uobj->pgops->pgo_get(uobj, (ufi.rvaddr - ufi.entry->start) +
				ufi.entry->offset, &uobjpage, &gotpages,
				0, UVM_ET_ISCOPYONWRITE(ufi.entry) ?
				VM_PROT_READ : access_type,
				ufi.entry->advice, 0);

    /* locked: uobjpage(if result OK) */

    /*
     * recover from I/O
     */

    if (result != VM_PAGER_OK) {

#ifdef DIAGNOSTIC
      if (result == VM_PAGER_PEND)
	panic("uvm_fault: pgo_get got PENDing on non-async I/O");
#endif

      if (result == VM_PAGER_AGAIN) {
	UVMHIST_LOG(maphist, "  pgo_get says TRY AGAIN!",0,0,0,0);
        tsleep((caddr_t)&lbolt, PVM, "fltagain2", 0);
	goto ReFault;
      }

      UVMHIST_LOG(maphist, "<- pgo_get failed (code %d)", result, 0,0,0);
      return(KERN_PROTECTION_FAILURE); /* XXX i/o error */
    }

    /* locked: uobjpage */

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

    locked = uvmfault_relock(&ufi);
    if (locked)
      simple_lock(&amap->am_l);
    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.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)
	thread_wakeup(uobjpage);	/* still holding object lock */

      if (uobjpage->flags & PG_RELEASED) {
        uvmexp.fltpgrele++;
#ifdef DIAGNOSTIC
	if (uobj->pgops->pgo_releasepg == NULL)
	  panic("uvm_fault: object has no releasepg function");
#endif
        if (uobj->pgops->pgo_releasepg(uobjpage,NULL))  /* frees page */
          simple_unlock(&uobj->vmobjlock);  /* unlock if still alive */
        goto ReFault;
      }

      uvm_lock_pageq();
      uvm_pageactivate(uobjpage);	/* make sure it is in queues */
      uvm_unlock_pageq();
      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 PG_BUSY and !PG_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) */
  /*
   * 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)
   */

  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)
     */

    uvmexp.flt_obj++;
    if (UVM_ET_ISCOPYONWRITE(ufi.entry))
      enter_prot = enter_prot & ~VM_PROT_WRITE;
    pg = uobjpage;		/* map in the actual object */

    /* assert(uobjpage != PGO_DONTCARE) */

    /*
     * we are faulting directly on the page.   be careful about writing
     * to loaned pages...
     */
    if (uobjpage->loan_count) {

      if ((access_type & VM_PROT_WRITE) == 0) {
	/* read fault: cap the protection at read-only */
	enter_prot = enter_prot & ~VM_PROT_WRITE;	/* cap! */

      } else {
	/* write fault: must break the loan here */
	pg = uvm_pagealloc(NULL, 0, NULL);	/* alloc new un-owned page */
	if (pg == NULL) {
	  /* drop ownership of page, it can't be released */
	  if (uobjpage->flags & PG_WANTED)
	    thread_wakeup(uobjpage);
	  uobjpage->flags &= ~(PG_BUSY|PG_WANTED);
	  UVM_PAGE_OWN(uobjpage, NULL);

	  uvm_lock_pageq();
	  uvm_pageactivate(uobjpage); /* activate: we will need it later */
	  uvm_unlock_pageq();
	  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;
	}

	/*
	 * copy the data from the old page to the new one and clear
	 * the fake/clean flags on the new page (keep it busy).
	 * force a reload of the old page by clearing it from all
	 * pmaps.
	 *
	 * then lock the page queues to rename the pages.
	 */
	uvm_pagecopy(uobjpage, pg);		/* old -> new */
	pg->flags &= ~(PG_FAKE|PG_CLEAN);
	pmap_page_protect(PMAP_PGARG(uobjpage), VM_PROT_NONE);
	if (uobjpage->flags & PG_WANTED)
	  thread_wakeup(uobjpage);
	uobjpage->flags &= ~(PG_WANTED|PG_BUSY);  /* uobj still locked */
	UVM_PAGE_OWN(uobjpage, NULL);

	uvm_lock_pageq();
	offset = uobjpage->offset;
	uvm_pagerealloc(uobjpage, NULL, 0);	/* remove old page */
	/* at this point we have absolutely no control over uobjpage */
	uvm_pagerealloc(pg, uobj, offset);	/* install new page */
	uvm_unlock_pageq();

	/*
	 * done!  loan is broken and "pg" is PG_BUSY.   it can now
	 * replace uobjpage.
	 */

	uobjpage = pg;

      }		/* write fault case */
    }		/* if loan_count */

  } 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

    anon = uvm_analloc();
    if (anon)
      pg = uvm_pagealloc(NULL, 0, anon);	/* BUSY+CLEAN+FAKE */
#if defined(sparc)
    else
      pg = NULL; /* XXX: shutup unused var compiler warning on sparc */
#endif

    /*
     * out of memory resources?
     */
    if (anon == NULL || pg == NULL) {

      /*
       * arg!  must unbusy our page and fail or sleep.
       */
      if (uobjpage != PGO_DONTCARE) {
	if (uobjpage->flags & PG_WANTED)
	  thread_wakeup(uobjpage);	/* still holding object lock */

	uvm_lock_pageq();
	uvm_pageactivate(uobjpage);	/* make sure it is in queues */
	uvm_unlock_pageq();
	uobjpage->flags &= ~(PG_BUSY|PG_WANTED); /* un-busy! (still locked) */
        UVM_PAGE_OWN(uobjpage, NULL);
      }

      /* unlock and fail ... */
      uvmfault_unlockall(&ufi, amap, uobj, NULL);
      if (anon == NULL) {
        UVMHIST_LOG(maphist, "  promote: out of VM", 0,0,0,0);
        uvmexp.fltnoanon++;
	return(KERN_RESOURCE_SHORTAGE);	/* XXX: out of VM */
      }
      UVMHIST_LOG(maphist, "  out of RAM, waiting for more",0,0,0,0);
      uvm_anfree(anon);
      uvmexp.fltnoram++;
      uvm_wait("flt_noram5");
      goto ReFault;
    }

    /*
     * fill in the data
     */

    if (uobjpage != PGO_DONTCARE) {
      uvmexp.flt_prcopy++;
      uvm_pagecopy(uobjpage, pg);	/* copy page [pg now dirty] */

      /* promote to shared amap?  make sure all sharing procs see it */
      if ((amap->am_flags & AMAP_SHARED) != 0) {
        pmap_page_protect(PMAP_PGARG(uobjpage), VM_PROT_NONE);
      }

      /*
       * 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)
	thread_wakeup(uobjpage);	/* still have the obj lock */
      uobjpage->flags &= ~(PG_BUSY|PG_WANTED);		/* un-busy! */
      UVM_PAGE_OWN(uobjpage, NULL);
      uvm_lock_pageq();
      uvm_pageactivate(uobjpage);	/* put it back */
      uvm_unlock_pageq();
      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++;
      uvm_pagezero(pg);			/* zero page [pg now dirty] */
      UVMHIST_LOG(maphist,"  zero fill anon/page 0x%x/0%x", anon, pg, 0, 0);
    }

    amap_add(&ufi.entry->aref, ufi.rvaddr - ufi.entry->start, anon, 0);

  }

  /* locked: maps(read), amap(if !null), uobj(if !null), uobjpage(if uobj) */
  /* note: pg is either the uobjpage or the new page in the new anon */

  /*
   * 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);
  pmap_enter(ufi.orig_map->pmap, ufi.orig_rvaddr, VM_PAGE_TO_PHYS(pg),
	     enter_prot, wired);

  uvm_lock_pageq();

  if (fault_type == VM_FAULT_WIRE) {

      uvm_pagewire(pg, FALSE);

  } else {

    /* activate it */
    if (pg == uobjpage)
      uvm_pagewire(pg, TRUE);	/* remove from q's before activating */
    uvm_pageactivate(pg);

  }

  uvm_unlock_pageq();

  if (pg->flags & PG_WANTED)
    thread_wakeup(pg);		/* lock still held */

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

  pg->flags &= ~(PG_BUSY|PG_FAKE|PG_WANTED);
  UVM_PAGE_OWN(pg, NULL);
  uvmfault_unlockall(&ufi, amap, uobj, NULL);

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


/*
 * uvm_fault_wire: wire down a range of virtual addresses in a map.
 *
 * => map should be locked by caller?   If so how can we call
 *	uvm_fault?   WRONG.
 * => XXXCDC: locking here is all screwed up!!!  start with
 *	uvm_map_pageable and fix it.
 */

int uvm_fault_wire(map, start, end)

vm_map_t map;
vm_offset_t start, end;

{
  vm_offset_t va;
  pmap_t  pmap;
  int rv;

  pmap = vm_map_pmap(map);

  /*
   * call pmap pageable: this tells the pmap layer to lock down these
   * page tables.
   */

  pmap_pageable(pmap, start, end, FALSE);

  /*
   * now fault it in 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.
   */

  for (va = start ; va < end ; va += PAGE_SIZE) {
    rv = uvm_fault(map, va, VM_FAULT_WIRE, VM_PROT_NONE);
    if (rv) {
      if (va != start) {
	uvm_fault_unwire(map->pmap, start, va);
      }
      return(rv);
    }
  }

  return(KERN_SUCCESS);
}

/*
 * uvm_fault_unwire(): unwire range of virtual space.
 *
 * => caller holds reference to pmap (via its map)
 */

void uvm_fault_unwire(pmap, start, end)

struct pmap *pmap;
vm_offset_t start, end;

{
  vm_offset_t va, 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.
   */

  uvm_lock_pageq();

  for (va = start; va < end ; va += PAGE_SIZE) {
    pa = pmap_extract(pmap, va);

    if (pa == (vm_offset_t) 0) { /* XXX: assumes PA 0 cannot be in map */
      panic("uvm_fault_unwire: unwiring non-wired memory");
    }
    pmap_change_wiring(pmap, va, FALSE);  /* tell the pmap */
    pg = PHYS_TO_VM_PAGE(pa);
    if (pg)
      uvm_pageunwire(pg);
  }

  uvm_unlock_pageq();

  /*
   * now we call pmap_pageable to let the pmap know that the page tables
   * in this space no longer need to be wired.
   */

  pmap_pageable(pmap, start, end, TRUE);

}