FreeBSD/Linux Kernel Cross Reference
sys/i386/i386/pmap.c

     /*
      * Copyright (c) 1991 Regents of the University of California.
      * All rights reserved.
      * Copyright (c) 1994 John S. Dyson
      * All rights reserved.
      * Copyright (c) 1994 David Greenman
      * All rights reserved.
      *
      * This code is derived from software contributed to Berkeley by
     * the Systems Programming Group of the University of Utah Computer
     * Science Department and William Jolitz of UUNET Technologies Inc.
     *
     * 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 the University of
     *      California, Berkeley and its contributors.
     * 4. Neither the name of the University nor the names of its contributors
     *    may be used to endorse or promote products derived from this software
     *    without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``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 REGENTS OR CONTRIBUTORS 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:   @(#)pmap.c      7.7 (Berkeley)  5/12/91
     * $FreeBSD: src/sys/i386/i386/pmap.c,v 1.128.2.8 1999/09/05 08:11:13 peter Exp $
     */
    
    /*
     *      Manages physical address maps.
     *
     *      In addition to hardware address maps, this
     *      module is called upon to provide software-use-only
     *      maps which may or may not be stored in the same
     *      form as hardware maps.  These pseudo-maps are
     *      used to store intermediate results from copy
     *      operations to and from address spaces.
     *
     *      Since the information managed by this module is
     *      also stored by the logical address mapping module,
     *      this module may throw away valid virtual-to-physical
     *      mappings at almost any time.  However, invalidations
     *      of virtual-to-physical mappings must be done as
     *      requested.
     *
     *      In order to cope with hardware architectures which
     *      make virtual-to-physical map invalidates expensive,
     *      this module may delay invalidate or reduced protection
     *      operations until such time as they are actually
     *      necessary.  This module is given full information as
     *      to which processors are currently using which maps,
     *      and to when physical maps must be made correct.
     */
    
    #include "opt_cpu.h"
    
    #define PMAP_LOCK 1
    #define PMAP_PVLIST 1
    
    #include "opt_msgbuf.h"
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/proc.h>
    #include <sys/malloc.h>
    #include <sys/msgbuf.h>
    #include <sys/queue.h>
    #include <sys/vmmeter.h>
    #include <sys/mman.h>
    
    #include <vm/vm.h>
    #include <vm/vm_param.h>
    #include <vm/vm_prot.h>
    #include <vm/lock.h>
    #include <vm/vm_kern.h>
    #include <vm/vm_page.h>
    #include <vm/vm_map.h>
    #include <vm/vm_object.h>
    #include <vm/vm_extern.h>
    #include <vm/vm_pageout.h>
    #include <vm/vm_pager.h>
    
    #include <machine/pcb.h>
   #include <machine/cputypes.h>
   #include <machine/md_var.h>
   #include <machine/specialreg.h>
   
   #define PMAP_KEEP_PDIRS
   #ifndef PMAP_SHPGPERPROC
   #define PMAP_SHPGPERPROC 200
   #endif
   
   #if defined(DIAGNOSTIC)
   #define PMAP_DIAGNOSTIC
   #endif
   
   #if !defined(PMAP_DIAGNOSTIC)
   #define PMAP_INLINE __inline
   #else
   #define PMAP_INLINE
   #endif
   
   #define PTPHINT
   
   static void     init_pv_entries __P((int));
   
   /*
    * Get PDEs and PTEs for user/kernel address space
    */
   #define pmap_pde(m, v)  (&((m)->pm_pdir[(vm_offset_t)(v) >> PDRSHIFT]))
   #define pdir_pde(m, v) (m[(vm_offset_t)(v) >> PDRSHIFT])
   
   #define pmap_pde_v(pte)         ((*(int *)pte & PG_V) != 0)
   #define pmap_pte_w(pte)         ((*(int *)pte & PG_W) != 0)
   #define pmap_pte_m(pte)         ((*(int *)pte & PG_M) != 0)
   #define pmap_pte_u(pte)         ((*(int *)pte & PG_A) != 0)
   #define pmap_pte_v(pte)         ((*(int *)pte & PG_V) != 0)
   
   #define pmap_pte_set_w(pte, v) ((v)?(*(int *)pte |= PG_W):(*(int *)pte &= ~PG_W))
   #define pmap_pte_set_prot(pte, v) ((*(int *)pte &= ~PG_PROT), (*(int *)pte |= (v)))
   
   /*
    * Given a map and a machine independent protection code,
    * convert to a vax protection code.
    */
   #define pte_prot(m, p)  (protection_codes[p])
   static int protection_codes[8];
   
   #define pa_index(pa)            atop((pa) - vm_first_phys)
   #define pa_to_pvh(pa)           (&pv_table[pa_index(pa)])
   
   static struct pmap kernel_pmap_store;
   pmap_t kernel_pmap;
   
   vm_offset_t avail_start;        /* PA of first available physical page */
   vm_offset_t avail_end;          /* PA of last available physical page */
   vm_offset_t virtual_avail;      /* VA of first avail page (after kernel bss) */
   vm_offset_t virtual_end;        /* VA of last avail page (end of kernel AS) */
   static boolean_t pmap_initialized = FALSE;      /* Has pmap_init completed? */
   static vm_offset_t vm_first_phys;
   static int pgeflag;             /* PG_G or-in */
   
   static int nkpt;
   static vm_page_t nkpg;
   vm_offset_t kernel_vm_end;
   
   extern vm_offset_t clean_sva, clean_eva;
   extern int cpu_class;
   
   #define PV_FREELIST_MIN ((PAGE_SIZE / sizeof (struct pv_entry)) / 2)
   
   /*
    * Data for the pv entry allocation mechanism
    */
   static int pv_freelistcnt;
   TAILQ_HEAD (,pv_entry) pv_freelist = {0};
   static vm_offset_t pvva;
   static int npvvapg;
   
   /*
    * All those kernel PT submaps that BSD is so fond of
    */
   pt_entry_t *CMAP1 = 0;
   static pt_entry_t *CMAP2, *ptmmap;
   static pv_table_t *pv_table;
   caddr_t CADDR1 = 0, ptvmmap = 0;
   static caddr_t CADDR2;
   static pt_entry_t *msgbufmap;
   struct msgbuf *msgbufp=0;
   
   pt_entry_t *PMAP1 = 0;
   unsigned *PADDR1 = 0;
   
   static PMAP_INLINE void free_pv_entry __P((pv_entry_t pv));
   static unsigned * get_ptbase __P((pmap_t pmap));
   static pv_entry_t get_pv_entry __P((void));
   static void     i386_protection_init __P((void));
   static void     pmap_alloc_pv_entry __P((void));
   static void     pmap_changebit __P((vm_offset_t pa, int bit, boolean_t setem));
   
   static PMAP_INLINE int  pmap_is_managed __P((vm_offset_t pa));
   static void     pmap_remove_all __P((vm_offset_t pa));
   static vm_page_t pmap_enter_quick __P((pmap_t pmap, vm_offset_t va,
                                         vm_offset_t pa, vm_page_t mpte));
   static int pmap_remove_pte __P((struct pmap *pmap, unsigned *ptq,
                                           vm_offset_t sva));
   static void pmap_remove_page __P((struct pmap *pmap, vm_offset_t va));
   static int pmap_remove_entry __P((struct pmap *pmap, pv_table_t *pv,
                                           vm_offset_t va));
   static boolean_t pmap_testbit __P((vm_offset_t pa, int bit));
   static void pmap_insert_entry __P((pmap_t pmap, vm_offset_t va,
                   vm_page_t mpte, vm_offset_t pa));
   
   static vm_page_t pmap_allocpte __P((pmap_t pmap, vm_offset_t va));
   
   static int pmap_release_free_page __P((pmap_t pmap, vm_page_t p));
   static vm_page_t _pmap_allocpte __P((pmap_t pmap, unsigned ptepindex));
   static unsigned * pmap_pte_quick __P((pmap_t pmap, vm_offset_t va));
   static vm_page_t pmap_page_alloc __P((vm_object_t object, vm_pindex_t pindex));
   static vm_page_t pmap_page_lookup __P((vm_object_t object, vm_pindex_t pindex));
   static int pmap_unuse_pt __P((pmap_t, vm_offset_t, vm_page_t));
   
   #define PDSTACKMAX 6
   static vm_offset_t pdstack[PDSTACKMAX];
   static int pdstackptr;
   
   /*
    *      Routine:        pmap_pte
    *      Function:
    *              Extract the page table entry associated
    *              with the given map/virtual_address pair.
    */
   
   PMAP_INLINE unsigned *
   pmap_pte(pmap, va)
           register pmap_t pmap;
           vm_offset_t va;
   {
           if (pmap && *pmap_pde(pmap, va)) {
                   return get_ptbase(pmap) + i386_btop(va);
           }
           return (0);
   }
   
   /*
    *      Bootstrap the system enough to run with virtual memory.
    *
    *      On the i386 this is called after mapping has already been enabled
    *      and just syncs the pmap module with what has already been done.
    *      [We can't call it easily with mapping off since the kernel is not
    *      mapped with PA == VA, hence we would have to relocate every address
    *      from the linked base (virtual) address "KERNBASE" to the actual
    *      (physical) address starting relative to 0]
    */
   void
   pmap_bootstrap(firstaddr, loadaddr)
           vm_offset_t firstaddr;
           vm_offset_t loadaddr;
   {
           vm_offset_t va;
           pt_entry_t *pte;
   
           avail_start = firstaddr;
   
           /*
            * XXX The calculation of virtual_avail is wrong. It's NKPT*PAGE_SIZE too
            * large. It should instead be correctly calculated in locore.s and
            * not based on 'first' (which is a physical address, not a virtual
            * address, for the start of unused physical memory). The kernel
            * page tables are NOT double mapped and thus should not be included
            * in this calculation.
            */
           virtual_avail = (vm_offset_t) KERNBASE + firstaddr;
           virtual_end = VM_MAX_KERNEL_ADDRESS;
   
           /*
            * Initialize protection array.
            */
           i386_protection_init();
   
           /*
            * The kernel's pmap is statically allocated so we don't have to use
            * pmap_create, which is unlikely to work correctly at this part of
            * the boot sequence (XXX and which no longer exists).
            */
           kernel_pmap = &kernel_pmap_store;
   
           kernel_pmap->pm_pdir = (pd_entry_t *) (KERNBASE + IdlePTD);
   
           kernel_pmap->pm_count = 1;
   #if PMAP_PVLIST
           TAILQ_INIT(&kernel_pmap->pm_pvlist);
   #endif
           nkpt = NKPT;
   
           /*
            * Reserve some special page table entries/VA space for temporary
            * mapping of pages.
            */
   #define SYSMAP(c, p, v, n)      \
           v = (c)va; va += ((n)*PAGE_SIZE); p = pte; pte += (n);
   
           va = virtual_avail;
           pte = (pt_entry_t *) pmap_pte(kernel_pmap, va);
   
           /*
            * CMAP1/CMAP2 are used for zeroing and copying pages.
            */
           SYSMAP(caddr_t, CMAP1, CADDR1, 1)
           SYSMAP(caddr_t, CMAP2, CADDR2, 1)
   
           /*
            * ptvmmap is used for reading arbitrary physical pages via /dev/mem.
            * XXX ptmmap is not used.
            */
           SYSMAP(caddr_t, ptmmap, ptvmmap, 1)
   
           /*
            * msgbufp is used to map the system message buffer.
            * XXX msgbufmap is not used.
            */
           SYSMAP(struct msgbuf *, msgbufmap, msgbufp,
                  atop(round_page(MSGBUF_SIZE)))
   
           /*
            * ptemap is used for pmap_pte_quick
            */
           SYSMAP(unsigned *, PMAP1, PADDR1, 1);
   
           virtual_avail = va;
   
           *(int *) CMAP1 = *(int *) CMAP2 = *(int *) PTD = 0;
           invltlb();
           if (cpu_feature & CPUID_PGE)
                   pgeflag = PG_G;
           else
                   pgeflag = 0;
   
   }
   
   /*
    *      Initialize the pmap module.
    *      Called by vm_init, to initialize any structures that the pmap
    *      system needs to map virtual memory.
    *      pmap_init has been enhanced to support in a fairly consistant
    *      way, discontiguous physical memory.
    */
   void
   pmap_init(phys_start, phys_end)
           vm_offset_t phys_start, phys_end;
   {
           vm_offset_t addr;
           vm_size_t s;
           int i, npg;
   
           /*
            * calculate the number of pv_entries needed
            */
           vm_first_phys = phys_avail[0];
           for (i = 0; phys_avail[i + 1]; i += 2);
           npg = (phys_avail[(i - 2) + 1] - vm_first_phys) / PAGE_SIZE;
   
           /*
            * Allocate memory for random pmap data structures.  Includes the
            * pv_head_table.
            */
           s = (vm_size_t) (sizeof(pv_table_t) * npg);
           s = round_page(s);
   
           addr = (vm_offset_t) kmem_alloc(kernel_map, s);
           pv_table = (pv_table_t *) addr;
           for(i = 0; i < npg; i++) {
                   vm_offset_t pa;
                   TAILQ_INIT(&pv_table[i].pv_list);
                   pv_table[i].pv_list_count = 0;
                   pa = vm_first_phys + i * PAGE_SIZE;
                   pv_table[i].pv_vm_page = PHYS_TO_VM_PAGE(pa);
           }
           TAILQ_INIT(&pv_freelist);
   
           /*
            * init the pv free list
            */
           init_pv_entries(npg);
           /*
            * Now it is safe to enable pv_table recording.
            */
           pmap_initialized = TRUE;
   }
   
   /*
    *      Used to map a range of physical addresses into kernel
    *      virtual address space.
    *
    *      For now, VM is already on, we only need to map the
    *      specified memory.
    */
   vm_offset_t
   pmap_map(virt, start, end, prot)
           vm_offset_t virt;
           vm_offset_t start;
           vm_offset_t end;
           int prot;
   {
           while (start < end) {
                   pmap_enter(kernel_pmap, virt, start, prot, FALSE);
                   virt += PAGE_SIZE;
                   start += PAGE_SIZE;
           }
           return (virt);
   }
   
   
   /***************************************************
    * Low level helper routines.....
    ***************************************************/
   
   #if defined(PMAP_DIAGNOSTIC)
   
   /*
    * This code checks for non-writeable/modified pages.
    * This should be an invalid condition.
    */
   static int
   pmap_nw_modified(pt_entry_t ptea) {
           int pte;
   
           pte = (int) ptea;
   
           if ((pte & (PG_M|PG_RW)) == PG_M)
                   return 1;
           else
                   return 0;
   }
   #endif
   
   
   /*
    * this routine defines the region(s) of memory that should
    * not be tested for the modified bit.
    */
   static PMAP_INLINE int
   pmap_track_modified( vm_offset_t va) {
           if ((va < clean_sva) || (va >= clean_eva)) 
                   return 1;
           else
                   return 0;
   }
   
   static PMAP_INLINE void
   invltlb_1pg( vm_offset_t va) {
   #if defined(I386_CPU)
           if (cpu_class == CPUCLASS_386) {
                   invltlb();
           } else
   #endif
           {
                   invlpg(va);
           }
   }
   
   static PMAP_INLINE void
   invltlb_2pg( vm_offset_t va1, vm_offset_t va2) {
   #if defined(I386_CPU)
           if (cpu_class == CPUCLASS_386) {
                   invltlb();
           } else
   #endif
           {
                   invlpg(va1);
                   invlpg(va2);
           }
   }
   
   static unsigned *
   get_ptbase(pmap)
           pmap_t pmap;
   {
           unsigned frame = (unsigned) pmap->pm_pdir[PTDPTDI] & PG_FRAME;
   
           /* are we current address space or kernel? */
           if (pmap == kernel_pmap || frame == (((unsigned) PTDpde) & PG_FRAME)) {
                   return (unsigned *) PTmap;
           }
           /* otherwise, we are alternate address space */
           if (frame != (((unsigned) APTDpde) & PG_FRAME)) {
                   APTDpde = (pd_entry_t) (frame | PG_RW | PG_V);
                   invltlb();
           }
           return (unsigned *) APTmap;
   }
   
   /*
    * Super fast pmap_pte routine best used when scanning
    * the pv lists.  This eliminates many coarse-grained
    * invltlb calls.  Note that many of the pv list
    * scans are across different pmaps.  It is very wasteful
    * to do an entire invltlb for checking a single mapping.
    */
   
   static unsigned * 
   pmap_pte_quick(pmap, va)
           register pmap_t pmap;
           vm_offset_t va;
   {
           unsigned pde, newpf;
           if (pde = (unsigned) pmap->pm_pdir[va >> PDRSHIFT]) {
                   unsigned frame = (unsigned) pmap->pm_pdir[PTDPTDI] & PG_FRAME;
                   unsigned index = i386_btop(va);
                   /* are we current address space or kernel? */
                   if ((pmap == kernel_pmap) ||
                           (frame == (((unsigned) PTDpde) & PG_FRAME))) {
                           return (unsigned *) PTmap + index;
                   }
                   newpf = pde & PG_FRAME;
                   if ( ((* (unsigned *) PMAP1) & PG_FRAME) != newpf) {
                           * (unsigned *) PMAP1 = newpf | PG_RW | PG_V;
                           invltlb_1pg((vm_offset_t) PADDR1);
                   }
                   return PADDR1 + ((unsigned) index & (NPTEPG - 1));
           }
           return (0);
   }
   
   /*
    *      Routine:        pmap_extract
    *      Function:
    *              Extract the physical page address associated
    *              with the given map/virtual_address pair.
    */
   vm_offset_t 
   pmap_extract(pmap, va)
           register pmap_t pmap;
           vm_offset_t va;
   {
           vm_offset_t rtval;
           if (pmap && *pmap_pde(pmap, va)) {
                   unsigned *pte;
                   pte = get_ptbase(pmap) + i386_btop(va);
                   rtval = ((*pte & PG_FRAME) | (va & PAGE_MASK));
                   return rtval;
           }
           return 0;
   
   }
   
   /*
    * determine if a page is managed (memory vs. device)
    */
   static PMAP_INLINE int
   pmap_is_managed(pa)
           vm_offset_t pa;
   {
           int i;
   
           if (!pmap_initialized)
                   return 0;
   
           for (i = 0; phys_avail[i + 1]; i += 2) {
                   if (pa < phys_avail[i + 1] && pa >= phys_avail[i])
                           return 1;
           }
           return 0;
   }
   
   
   /***************************************************
    * Low level mapping routines.....
    ***************************************************/
   
   /*
    * Add a list of wired pages to the kva
    * this routine is only used for temporary
    * kernel mappings that do not need to have
    * page modification or references recorded.
    * Note that old mappings are simply written
    * over.  The page *must* be wired.
    */
   void
   pmap_qenter(va, m, count)
           vm_offset_t va;
           vm_page_t *m;
           int count;
   {
           int i;
           register unsigned *pte;
   
           for (i = 0; i < count; i++) {
                   vm_offset_t tva = va + i * PAGE_SIZE;
                   unsigned npte = VM_PAGE_TO_PHYS(m[i]) | PG_RW | PG_V | pgeflag;
                   unsigned opte;
                   pte = (unsigned *)vtopte(tva);
                   opte = *pte;
                   *pte = npte;
                   if (opte)
                           invltlb_1pg(tva);
           }
   }
   
   /*
    * this routine jerks page mappings from the
    * kernel -- it is meant only for temporary mappings.
    */
   void
   pmap_qremove(va, count)
           vm_offset_t va;
           int count;
   {
           int i;
           register unsigned *pte;
   
           for (i = 0; i < count; i++) {
                   pte = (unsigned *)vtopte(va);
                   *pte = 0;
                   invltlb_1pg(va);
                   va += PAGE_SIZE;
           }
   }
   
   /*
    * add a wired page to the kva
    * note that in order for the mapping to take effect -- you
    * should do a invltlb after doing the pmap_kenter...
    */
   PMAP_INLINE void 
   pmap_kenter(va, pa)
           vm_offset_t va;
           register vm_offset_t pa;
   {
           register unsigned *pte;
           unsigned npte, opte;
   
           npte = pa | PG_RW | PG_V | pgeflag;
           pte = (unsigned *)vtopte(va);
           opte = *pte;
           *pte = npte;
           if (opte)
                   invltlb_1pg(va);
   }
   
   /*
    * remove a page from the kernel pagetables
    */
   PMAP_INLINE void
   pmap_kremove(va)
           vm_offset_t va;
   {
           register unsigned *pte;
   
           pte = (unsigned *)vtopte(va);
           *pte = 0;
           invltlb_1pg(va);
   }
   
   static vm_page_t
   pmap_page_alloc(object, pindex)
           vm_object_t object;
           vm_pindex_t pindex;
   {
           vm_page_t m;
           m = vm_page_alloc(object, pindex, VM_ALLOC_ZERO);
           if (m == NULL) {
                   VM_WAIT;
           }
           return m;
   }
   
   static vm_page_t
   pmap_page_lookup(object, pindex)
           vm_object_t object;
           vm_pindex_t pindex;
   {
           vm_page_t m;
   retry:
           m = vm_page_lookup(object, pindex);
           if (m) {
                   if (m->flags & PG_BUSY) {
                           m->flags |= PG_WANTED;
                           tsleep(m, PVM, "pplookp", 0);
                           goto retry;
                   }
           }
   
           return m;
   }
   
   /*
    * Create the UPAGES for a new process.
    * This routine directly affects the fork perf for a process.
    */
   void
   pmap_new_proc(p)
           struct proc *p;
   {
           int i;
           vm_object_t upobj;
           pmap_t pmap;
           vm_page_t m;
           struct user *up;
           unsigned *ptep, *ptek;
   
           pmap = &p->p_vmspace->vm_pmap;
   
           /*
            * allocate object for the upages
            */
           upobj = vm_object_allocate( OBJT_DEFAULT,
                   UPAGES);
           p->p_vmspace->vm_upages_obj = upobj;
   
           /* get a kernel virtual address for the UPAGES for this proc */
           up = (struct user *) kmem_alloc_pageable(u_map, UPAGES * PAGE_SIZE);
           if (up == NULL)
                   panic("vm_fork: u_map allocation failed");
   
           /*
            * Allocate the ptp and incr the hold count appropriately
            */
           m = pmap_allocpte(pmap, (vm_offset_t) kstack);
           m->hold_count += (UPAGES - 1);
   
           ptep = (unsigned *) pmap_pte(pmap, (vm_offset_t) kstack);
           ptek = (unsigned *) vtopte((vm_offset_t) up);
   
           for(i=0;i<UPAGES;i++) {
                   /*
                    * Get a kernel stack page
                    */
                   while ((m = vm_page_alloc(upobj,
                           i, VM_ALLOC_NORMAL)) == NULL) {
                           VM_WAIT;
                   }
   
                   /*
                    * Wire the page
                    */
                   m->wire_count++;
                   ++cnt.v_wire_count;
   
                   /*
                    * Enter the page into both the kernel and the process
                    * address space.
                    */
                   *(ptep + i) = VM_PAGE_TO_PHYS(m) | PG_RW | PG_V;
                   *(ptek + i) = VM_PAGE_TO_PHYS(m) | PG_RW | PG_V;
   
                   m->flags &= ~(PG_ZERO|PG_BUSY);
                   m->flags |= PG_MAPPED|PG_WRITEABLE;
                   m->valid = VM_PAGE_BITS_ALL;
           }
   
           pmap->pm_stats.resident_count += UPAGES;
           p->p_addr = up;
   }
   
   /*
    * Dispose the UPAGES for a process that has exited.
    * This routine directly impacts the exit perf of a process.
    */
   void
   pmap_dispose_proc(p)
           struct proc *p;
   {
           int i;
           vm_object_t upobj;
           pmap_t pmap;
           vm_page_t m;
           unsigned *ptep, *ptek;
   
           pmap = &p->p_vmspace->vm_pmap;
           ptep = (unsigned *) pmap_pte(pmap, (vm_offset_t) kstack);
           ptek = (unsigned *) vtopte((vm_offset_t) p->p_addr);
   
           upobj = p->p_vmspace->vm_upages_obj;
   
           for(i=0;i<UPAGES;i++) {
                   if ((m = vm_page_lookup(upobj, i)) == NULL)
                           panic("pmap_dispose_proc: upage already missing???");
                   *(ptep + i) = 0;
                   *(ptek + i) = 0;
                   pmap_unuse_pt(pmap, (vm_offset_t) kstack + i * PAGE_SIZE, NULL);
                   vm_page_unwire(m);
                   vm_page_free(m);
           }
           pmap->pm_stats.resident_count -= UPAGES;
   
           kmem_free(u_map, (vm_offset_t)p->p_addr, ctob(UPAGES));
   }
   
   /*
    * Allow the UPAGES for a process to be prejudicially paged out.
    */
   void
   pmap_swapout_proc(p)
           struct proc *p;
   {
           int i;
           vm_object_t upobj;
           pmap_t pmap;
           vm_page_t m;
           unsigned *pte;
   
           pmap = &p->p_vmspace->vm_pmap;
           pte = (unsigned *) pmap_pte(pmap, (vm_offset_t) kstack);
   
           upobj = p->p_vmspace->vm_upages_obj;
           /*
            * let the upages be paged
            */
           for(i=0;i<UPAGES;i++) {
                   if ((m = vm_page_lookup(upobj, i)) == NULL)
                           panic("pmap_pageout_proc: upage already missing???");
                   m->dirty = VM_PAGE_BITS_ALL;
                   *(pte + i) = 0;
                   pmap_unuse_pt(pmap, (vm_offset_t) kstack + i * PAGE_SIZE, NULL);
   
                   vm_page_unwire(m);
                   vm_page_deactivate(m);
                   pmap_kremove( (vm_offset_t) p->p_addr + PAGE_SIZE * i);
           }
           pmap->pm_stats.resident_count -= UPAGES;
   }
   
   /*
    * Bring the UPAGES for a specified process back in.
    */
   void
   pmap_swapin_proc(p)
           struct proc *p;
   {
           int i;
           vm_object_t upobj;
           pmap_t pmap;
           vm_page_t m;
           unsigned *pte;
   
           pmap = &p->p_vmspace->vm_pmap;
           /*
            * Allocate the ptp and incr the hold count appropriately
            */
           m = pmap_allocpte(pmap, (vm_offset_t) kstack);
           m->hold_count += (UPAGES - 1);
           pte = (unsigned *) pmap_pte(pmap, (vm_offset_t) kstack);
   
           upobj = p->p_vmspace->vm_upages_obj;
           for(i=0;i<UPAGES;i++) {
                   int s;
                   s = splvm();
   retry:
                   if ((m = vm_page_lookup(upobj, i)) == NULL) {
                           if ((m = vm_page_alloc(upobj, i, VM_ALLOC_NORMAL)) == NULL) {
                                   VM_WAIT;
                                   goto retry;
                           }
                   } else {
                           if ((m->flags & PG_BUSY) || m->busy) {
                                   m->flags |= PG_WANTED;
                                   tsleep(m, PVM, "swinuw",0);
                                   goto retry;
                           }
                           m->flags |= PG_BUSY;
                   }
                   vm_page_wire(m);
                   splx(s);
   
                   *(pte+i) = VM_PAGE_TO_PHYS(m) | PG_RW | PG_V;
                   pmap_kenter(((vm_offset_t) p->p_addr) + i * PAGE_SIZE,
                           VM_PAGE_TO_PHYS(m));
   
                   if (m->valid != VM_PAGE_BITS_ALL) {
                           int rv;
                           rv = vm_pager_get_pages(upobj, &m, 1, 0);
                           if (rv != VM_PAGER_OK)
                                   panic("faultin: cannot get upages for proc: %d\n", p->p_pid);
                           m->valid = VM_PAGE_BITS_ALL;
                   }
                   PAGE_WAKEUP(m);
                   m->flags |= PG_MAPPED|PG_WRITEABLE;
           }
           pmap->pm_stats.resident_count += UPAGES;
   }
   
   /***************************************************
    * Page table page management routines.....
    ***************************************************/
   
   /*
    * This routine unholds page table pages, and if the hold count
    * drops to zero, then it decrements the wire count.
    */
   static int 
   _pmap_unwire_pte_hold(pmap_t pmap, vm_page_t m) {
           int s;
   
           if (m->flags & PG_BUSY) {
                   s = splvm();
                   while (m->flags & PG_BUSY) {
                           m->flags |= PG_WANTED;
                           tsleep(m, PVM, "pmuwpt", 0);
                   }
                   splx(s);
           }
   
           if (m->hold_count == 0) {
                   vm_offset_t pteva;
                   /*
                    * unmap the page table page
                    */
                   pmap->pm_pdir[m->pindex] = 0;
                   --pmap->pm_stats.resident_count;
                   if ((((unsigned)pmap->pm_pdir[PTDPTDI]) & PG_FRAME) ==
                           (((unsigned) PTDpde) & PG_FRAME)) {
                           /*
                            * Do a invltlb to make the invalidated mapping
                            * take effect immediately.
                            */
                           pteva = UPT_MIN_ADDRESS + i386_ptob(m->pindex);
                           invltlb_1pg(pteva);
                   }
   
   #if defined(PTPHINT)
                   if (pmap->pm_ptphint == m)
                           pmap->pm_ptphint = NULL;
   #endif
   
                   /*
                    * If the page is finally unwired, simply free it.
                    */
                   --m->wire_count;
                   if (m->wire_count == 0) {
   
                           if (m->flags & PG_WANTED) {
                                   m->flags &= ~PG_WANTED;
                                   wakeup(m);
                           }
   
                           vm_page_free_zero(m);
                           --cnt.v_wire_count;
                   }
                   return 1;
           }
           return 0;
   }
   
   __inline static int
   pmap_unwire_pte_hold(pmap_t pmap, vm_page_t m) {
           vm_page_unhold(m);
           if (m->hold_count == 0)
                   return _pmap_unwire_pte_hold(pmap, m);
           else
                   return 0;
   }
   
   /*
    * After removing a page table entry, this routine is used to
    * conditionally free the page, and manage the hold/wire counts.
    */
   static int
   pmap_unuse_pt(pmap, va, mpte)
           pmap_t pmap;
           vm_offset_t va;
           vm_page_t mpte;
   {
           unsigned ptepindex;
           if (va >= UPT_MIN_ADDRESS)
                   return 0;
   
           if (mpte == NULL) {
                   ptepindex = (va >> PDRSHIFT);
   #if defined(PTPHINT)
                   if (pmap->pm_ptphint &&
                           (pmap->pm_ptphint->pindex == ptepindex)) {
                           mpte = pmap->pm_ptphint;
                   } else {
                           mpte = pmap_page_lookup( pmap->pm_pteobj, ptepindex);
                           pmap->pm_ptphint = mpte;
                   }
   #else
                   mpte = pmap_page_lookup( pmap->pm_pteobj, ptepindex);
   #endif
           }
   
           return pmap_unwire_pte_hold(pmap, mpte);
   }
   
   /*
    * Initialize a preallocated and zeroed pmap structure,
    * such as one in a vmspace structure.
    */
   void
   pmap_pinit(pmap)
           register struct pmap *pmap;
   {
           vm_page_t ptdpg;
           /*
            * No need to allocate page table space yet but we do need a valid
            * page directory table.
            */
   
           if (pdstackptr > 0) {
                   --pdstackptr;
                   pmap->pm_pdir = (pd_entry_t *)pdstack[pdstackptr];
           } else {
                  pmap->pm_pdir =
                          (pd_entry_t *)kmem_alloc_pageable(kernel_map, PAGE_SIZE);
          }
  
          /*
           * allocate object for the ptes
           */
          pmap->pm_pteobj = vm_object_allocate( OBJT_DEFAULT, PTDPTDI + 1);
  
          /*
           * allocate the page directory page
           */
  retry:
          ptdpg = pmap_page_alloc( pmap->pm_pteobj, PTDPTDI);
          if (ptdpg == NULL) 
                  goto retry;
  
          ptdpg->wire_count = 1;
          ++cnt.v_wire_count;
  
          ptdpg->flags &= ~(PG_MAPPED|PG_BUSY);   /* not mapped normally */
          ptdpg->valid = VM_PAGE_BITS_ALL;
  
          pmap_kenter((vm_offset_t) pmap->pm_pdir, VM_PAGE_TO_PHYS(ptdpg));
          if ((ptdpg->flags & PG_ZERO) == 0)
                  bzero(pmap->pm_pdir, PAGE_SIZE);
  
          /* wire in kernel global address entries */
          bcopy(PTD + KPTDI, pmap->pm_pdir + KPTDI, nkpt * PTESIZE);
  
          /* install self-referential address mapping entry */
          *(unsigned *) (pmap->pm_pdir + PTDPTDI) =
                  VM_PAGE_TO_PHYS(ptdpg) | PG_V | PG_RW;
  
          pmap->pm_flags = 0;
          pmap->pm_count = 1;
          pmap->pm_ptphint = NULL;
  #if PMAP_PVLIST
          TAILQ_INIT(&pmap->pm_pvlist);
  #endif
  }
  
  static int
  pmap_release_free_page(pmap, p)
          struct pmap *pmap;
          vm_page_t p;
  {
          int s;
          unsigned *pde = (unsigned *) pmap->pm_pdir;
          /*
           * This code optimizes the case of freeing non-busy
           * page-table pages.  Those pages are zero now, and
           * might as well be placed directly into the zero queue.
           */
          s = splvm();
          if (p->flags & PG_BUSY) {
                  p->flags |= PG_WANTED;
                  tsleep(p, PVM, "pmaprl", 0);
                  splx(s);
                  return 0;
          }
  
          if (p->flags & PG_WANTED) {
                  p->flags &= ~PG_WANTED;
                  wakeup(p);
          }
  
          /*
           * Remove the page table page from the processes address space.
           */
          pde[p->pindex] = 0;
          --pmap->pm_stats.resident_count;
  
          if (p->hold_count)  {
                  panic("pmap_release: freeing held page table page");
          }
          /*
           * Page directory pages need to have the kernel
           * stuff cleared, so they can go into the zero queue also.
           */
          if (p->pindex == PTDPTDI) {
                  bzero(pde + KPTDI, nkpt * PTESIZE);
                  pde[APTDPTDI] = 0;
                  pmap_kremove((vm_offset_t) pmap->pm_pdir);
          }
  
  #if defined(PTPHINT)
          if (pmap->pm_ptphint &&
                  (pmap->pm_ptphint->pindex == p->pindex))
                  pmap->pm_ptphint = NULL;
  #endif
  
          vm_page_free_zero(p);
          splx(s);
          return 1;
  }
  
  /*
   * this routine is called if the page table page is not
   * mapped correctly.
   */
  static vm_page_t
  _pmap_allocpte(pmap, ptepindex)
          pmap_t  pmap;
          unsigned ptepindex;
  {
          vm_offset_t pteva, ptepa;
          vm_page_t m;
          int needszero = 0;
  
          /*
           * Find or fabricate a new pagetable page
           */
  retry:
          m = vm_page_lookup(pmap->pm_pteobj, ptepindex);
          if (m == NULL) {
                  m = pmap_page_alloc(pmap->pm_pteobj, ptepindex);
                  if (m == NULL)
                          goto retry;
                  if ((m->flags & PG_ZERO) == 0)
                          needszero = 1;
                  m->flags &= ~(PG_ZERO|PG_BUSY);
                  m->valid = VM_PAGE_BITS_ALL;
          } else {
                  if ((m->flags & PG_BUSY) || m->busy) {
                          m->flags |= PG_WANTED;
                          tsleep(m, PVM, "ptewai", 0);
                          goto retry;
                  }
          }
  
          if (m->queue != PQ_NONE) {
                  int s = splvm();
                  vm_page_unqueue(m);
                  splx(s);
          }
  
          if (m->wire_count == 0)
                  ++cnt.v_wire_count;
          ++m->wire_count;
  
          /*
           * Increment the hold count for the page table page
           * (denoting a new mapping.)
           */
          ++m->hold_count;
  
          /*
           * Map the pagetable page into the process address space, if
           * it isn't already there.
           */
  
          pmap->pm_stats.resident_count++;
  
          ptepa = VM_PAGE_TO_PHYS(m);
          pmap->pm_pdir[ptepindex] = (pd_entry_t) (ptepa | PG_U | PG_RW | PG_V);
  
  #if defined(PTPHINT)
          /*
           * Set the page table hint
           */
          pmap->pm_ptphint = m;
  #endif
  
          /*
           * Try to use the new mapping, but if we cannot, then
           * do it with the routine that maps the page explicitly.
           */
          if (needszero) {
                  if ((((unsigned)pmap->pm_pdir[PTDPTDI]) & PG_FRAME) ==
                          (((unsigned) PTDpde) & PG_FRAME)) {
                          pteva = UPT_MIN_ADDRESS + i386_ptob(ptepindex);
                          bzero((caddr_t) pteva, PAGE_SIZE);
                  } else {
                          pmap_zero_page(ptepa);
                  }
          }
  
          m->valid = VM_PAGE_BITS_ALL;
          m->flags |= PG_MAPPED;
  
          return m;
  }
  
  static vm_page_t
  pmap_allocpte(pmap, va)
          pmap_t  pmap;
          vm_offset_t va;
  {
          unsigned ptepindex;
          vm_offset_t ptepa;
          vm_page_t m;
  
          /*
           * Calculate pagetable page index
           */
          ptepindex = va >> PDRSHIFT;
  
          /*
           * Get the page directory entry
           */
          ptepa = (vm_offset_t) pmap->pm_pdir[ptepindex];
  
          /*
           * If the page table page is mapped, we just increment the
           * hold count, and activate it.
           */
          if (ptepa) {
  #if defined(PTPHINT)
                  /*
                   * In order to get the page table page, try the
                   * hint first.
                   */
                  if (pmap->pm_ptphint &&
                          (pmap->pm_ptphint->pindex == ptepindex)) {
                          m = pmap->pm_ptphint;
                  } else {
                          m = pmap_page_lookup( pmap->pm_pteobj, ptepindex);
                          pmap->pm_ptphint = m;
                  }
  #else
                  m = pmap_page_lookup( pmap->pm_pteobj, ptepindex);
  #endif
                  ++m->hold_count;
                  return m;
          }
          /*
           * Here if the pte page isn't mapped, or if it has been deallocated.
           */
          return _pmap_allocpte(pmap, ptepindex);
  }
  
  
  /***************************************************
  * Pmap allocation/deallocation routines.
   ***************************************************/
  
  /*
   * Release any resources held by the given physical map.
   * Called when a pmap initialized by pmap_pinit is being released.
   * Should only be called if the map contains no valid mappings.
   */
  void
  pmap_release(pmap)
          register struct pmap *pmap;
  {
          vm_page_t p,n,ptdpg;
          vm_object_t object = pmap->pm_pteobj;
  
  #if defined(DIAGNOSTIC)
          if (object->ref_count != 1)
                  panic("pmap_release: pteobj reference count != 1");
  #endif
          
          ptdpg = NULL;
  retry:
          for (p = TAILQ_FIRST(&object->memq); p != NULL; p = n) {
                  n = TAILQ_NEXT(p, listq);
                  if (p->pindex == PTDPTDI) {
                          ptdpg = p;
                          continue;
                  }
                  if (!pmap_release_free_page(pmap, p))
                          goto retry;
          }
  
          if (ptdpg && !pmap_release_free_page(pmap, ptdpg))
                  goto retry;
                  
          vm_object_deallocate(object);
          if (pdstackptr < PDSTACKMAX) {
                  pdstack[pdstackptr] = (vm_offset_t) pmap->pm_pdir;
                  ++pdstackptr;
          } else {
                  kmem_free(kernel_map, (vm_offset_t) pmap->pm_pdir, PAGE_SIZE);
          }
          pmap->pm_pdir = 0;
  }
  
  /*
   * grow the number of kernel page table entries, if needed
   */
  void
  pmap_growkernel(vm_offset_t addr)
  {
          struct proc *p;
          struct pmap *pmap;
          int s;
  
          s = splhigh();
          if (kernel_vm_end == 0) {
                  kernel_vm_end = KERNBASE;
                  nkpt = 0;
                  while (pdir_pde(PTD, kernel_vm_end)) {
                          kernel_vm_end = (kernel_vm_end + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);
                          ++nkpt;
                  }
          }
          addr = (addr + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);
          while (kernel_vm_end < addr) {
                  if (pdir_pde(PTD, kernel_vm_end)) {
                          kernel_vm_end = (kernel_vm_end + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);
                          continue;
                  }
                  ++nkpt;
                  if (!nkpg) {
                          vm_offset_t ptpkva = (vm_offset_t) vtopte(addr);
                          /*
                           * This index is bogus, but out of the way
                           */
                          vm_pindex_t ptpidx = (ptpkva >> PAGE_SHIFT); 
                          nkpg = vm_page_alloc(kernel_object,
                                  ptpidx, VM_ALLOC_SYSTEM);
                          if (!nkpg)
                                  panic("pmap_growkernel: no memory to grow kernel");
                          vm_page_wire(nkpg);
                          vm_page_remove(nkpg);
                          pmap_zero_page(VM_PAGE_TO_PHYS(nkpg));
                  }
                  pdir_pde(PTD, kernel_vm_end) = (pd_entry_t) (VM_PAGE_TO_PHYS(nkpg) | PG_V | PG_RW);
                  nkpg = NULL;
  
                  for (p = allproc.lh_first; p != 0; p = p->p_list.le_next) {
                          if (p->p_vmspace) {
                                  pmap = &p->p_vmspace->vm_pmap;
                                  *pmap_pde(pmap, kernel_vm_end) = pdir_pde(PTD, kernel_vm_end);
                          }
                  }
                  *pmap_pde(kernel_pmap, kernel_vm_end) = pdir_pde(PTD, kernel_vm_end);
                  kernel_vm_end = (kernel_vm_end + PAGE_SIZE * NPTEPG) & ~(PAGE_SIZE * NPTEPG - 1);
          }
          splx(s);
  }
  
  /*
   *      Retire the given physical map from service.
   *      Should only be called if the map contains
   *      no valid mappings.
   */
  void
  pmap_destroy(pmap)
          register pmap_t pmap;
  {
          int count;
  
          if (pmap == NULL)
                  return;
  
          count = --pmap->pm_count;
          if (count == 0) {
                  pmap_release(pmap);
                  free((caddr_t) pmap, M_VMPMAP);
          }
  }
  
  /*
   *      Add a reference to the specified pmap.
   */
  void
  pmap_reference(pmap)
          pmap_t pmap;
  {
          if (pmap != NULL) {
                  pmap->pm_count++;
          }
  }
  
  /***************************************************
  * page management routines.
   ***************************************************/
  
  /*
   * free the pv_entry back to the free list
   */
  static PMAP_INLINE void
  free_pv_entry(pv)
          pv_entry_t pv;
  {
          ++pv_freelistcnt;
          TAILQ_INSERT_HEAD(&pv_freelist, pv, pv_list);
  }
  
  /*
   * get a new pv_entry, allocating a block from the system
   * when needed.
   * the memory allocation is performed bypassing the malloc code
   * because of the possibility of allocations at interrupt time.
   */
  static pv_entry_t
  get_pv_entry()
  {
          pv_entry_t tmp;
  
          /*
           * get more pv_entry pages if needed
           */
          if (pv_freelistcnt < PV_FREELIST_MIN || !TAILQ_FIRST(&pv_freelist)) {
                  pmap_alloc_pv_entry();
          }
          /*
           * get a pv_entry off of the free list
           */
          --pv_freelistcnt;
          tmp = TAILQ_FIRST(&pv_freelist);
          TAILQ_REMOVE(&pv_freelist, tmp, pv_list);
          return tmp;
  }
  
  /*
   * This *strange* allocation routine eliminates the possibility of a malloc
   * failure (*FATAL*) for a pv_entry_t data structure.
   * also -- this code is MUCH MUCH faster than the malloc equiv...
   * We really need to do the slab allocator thingie here.
   */
  static void
  pmap_alloc_pv_entry()
  {
          /*
           * do we have any pre-allocated map-pages left?
           */
          if (npvvapg) {
                  vm_page_t m;
  
                  /*
                   * allocate a physical page out of the vm system
                   */
                  m = vm_page_alloc(kernel_object,
                      OFF_TO_IDX(pvva - vm_map_min(kernel_map)),
                      VM_ALLOC_INTERRUPT);
                  if (m) {
                          int newentries;
                          int i;
                          pv_entry_t entry;
  
                          newentries = (PAGE_SIZE / sizeof(struct pv_entry));
                          /*
                           * wire the page
                           */
                          vm_page_wire(m);
                          m->flags &= ~PG_BUSY;
                          /*
                           * let the kernel see it
                           */
                          pmap_kenter(pvva, VM_PAGE_TO_PHYS(m));
  
                          entry = (pv_entry_t) pvva;
                          /*
                           * update the allocation pointers
                           */
                          pvva += PAGE_SIZE;
                          --npvvapg;
  
                          /*
                           * free the entries into the free list
                           */
                          for (i = 0; i < newentries; i++) {
                                  free_pv_entry(entry);
                                  entry++;
                          }
                  }
          }
          if (!TAILQ_FIRST(&pv_freelist))
                  panic("get_pv_entry: cannot get a pv_entry_t");
  }
  
  /*
   * init the pv_entry allocation system
   */
  void
  init_pv_entries(npg)
          int npg;
  {
          /*
           * Allocate enough kvm space for one entry per page, and
           * each process having PMAP_SHPGPERPROC pages shared with other
           * processes.  (The system can panic if this is too small, but also
           * can fail on bootup if this is too big.)
           * XXX The pv management mechanism needs to be fixed so that systems
           * with lots of shared mappings amongst lots of processes will still
           * work.  The fix will likely be that once we run out of pv entries
           * we will free other entries (and the associated mappings), with
           * some policy yet to be determined.
           */
          npvvapg = ((PMAP_SHPGPERPROC * maxproc + npg) * sizeof(struct pv_entry)
                  + PAGE_SIZE - 1) / PAGE_SIZE;
          pvva = kmem_alloc_pageable(kernel_map, npvvapg * PAGE_SIZE);
          /*
           * get the first batch of entries
           */
          pmap_alloc_pv_entry();
  }
  
  /*
   * If it is the first entry on the list, it is actually
   * in the header and we must copy the following entry up
   * to the header.  Otherwise we must search the list for
   * the entry.  In either case we free the now unused entry.
   */
  
  static int
  pmap_remove_entry(pmap, ppv, va)
          struct pmap *pmap;
          pv_table_t *ppv;
          vm_offset_t va;
  {
          pv_entry_t pv;
          int rtval;
          int s;
  
          s = splvm();
  #if PMAP_PVLIST
          if (ppv->pv_list_count < pmap->pm_stats.resident_count) {
  #endif
                  for (pv = TAILQ_FIRST(&ppv->pv_list);
                          pv;
                          pv = TAILQ_NEXT(pv, pv_list)) {
                          if (pmap == pv->pv_pmap && va == pv->pv_va) 
                                  break;
                  }
  #if PMAP_PVLIST
          } else {
                  for (pv = TAILQ_FIRST(&pmap->pm_pvlist);
                          pv;
                          pv = TAILQ_NEXT(pv, pv_plist)) {
                          if (va == pv->pv_va) 
                                  break;
                  }
          }
  #endif
  
          rtval = 0;
          if (pv) {
                  rtval = pmap_unuse_pt(pmap, va, pv->pv_ptem);
                  TAILQ_REMOVE(&ppv->pv_list, pv, pv_list);
                  --ppv->pv_list_count;
                  if (TAILQ_FIRST(&ppv->pv_list) == NULL) {
                          ppv->pv_vm_page->flags &= ~(PG_MAPPED|PG_WRITEABLE);
                  }
  
  #if PMAP_PVLIST
                  TAILQ_REMOVE(&pmap->pm_pvlist, pv, pv_plist);
  #endif
                  free_pv_entry(pv);
          }
                          
          splx(s);
          return rtval;
  }
  
  /*
   * Create a pv entry for page at pa for
   * (pmap, va).
   */
  static void
  pmap_insert_entry(pmap, va, mpte, pa)
          pmap_t pmap;
          vm_offset_t va;
          vm_page_t mpte;
          vm_offset_t pa;
  {
  
          int s;
          pv_entry_t pv;
          pv_table_t *ppv;
  
          s = splvm();
          pv = get_pv_entry();
          pv->pv_va = va;
          pv->pv_pmap = pmap;
          pv->pv_ptem = mpte;
  
  #if PMAP_PVLIST
          TAILQ_INSERT_TAIL(&pmap->pm_pvlist, pv, pv_plist);
  #endif
  
          ppv = pa_to_pvh(pa);
          TAILQ_INSERT_TAIL(&ppv->pv_list, pv, pv_list);
          ++ppv->pv_list_count;
  
          splx(s);
  }
  
  /*
   * pmap_remove_pte: do the things to unmap a page in a process
   */
  static int
  pmap_remove_pte(pmap, ptq, va)
          struct pmap *pmap;
          unsigned *ptq;
          vm_offset_t va;
  {
          unsigned oldpte;
          pv_table_t *ppv;
  
          oldpte = *ptq;
          *ptq = 0;
          if (oldpte & PG_W)
                  pmap->pm_stats.wired_count -= 1;
          /*
           * Machines that don't support invlpg, also don't support
           * PG_G.
           */
          if (oldpte & PG_G)
                  invlpg(va);
          pmap->pm_stats.resident_count -= 1;
          if (oldpte & PG_MANAGED) {
                  ppv = pa_to_pvh(oldpte);
                  if (oldpte & PG_M) {
  #if defined(PMAP_DIAGNOSTIC)
                          if (pmap_nw_modified((pt_entry_t) oldpte)) {
                                  printf("pmap_remove: modified page not writable: va: 0x%lx, pte: 0x%lx\n", va, (int) oldpte);
                          }
  #endif
                          if (pmap_track_modified(va))
                                  ppv->pv_vm_page->dirty = VM_PAGE_BITS_ALL;
                  }
                  return pmap_remove_entry(pmap, ppv, va);
          } else {
                  return pmap_unuse_pt(pmap, va, NULL);
          }
  
          return 0;
  }
  
  /*
   * Remove a single page from a process address space
   */
  static void
  pmap_remove_page(pmap, va)
          struct pmap *pmap;
          register vm_offset_t va;
  {
          register unsigned *ptq;
  
          /*
           * if there is no pte for this address, just skip it!!!
           */
          if (*pmap_pde(pmap, va) == 0) {
                  return;
          }
  
          /*
           * get a local va for mappings for this pmap.
           */
          ptq = get_ptbase(pmap) + i386_btop(va);
          if (*ptq) {
                  (void) pmap_remove_pte(pmap, ptq, va);
                  invltlb_1pg(va);
          }
          return;
  }
  
  /*
   *      Remove the given range of addresses from the specified map.
   *
   *      It is assumed that the start and end are properly
   *      rounded to the page size.
   */
  void
  pmap_remove(pmap, sva, eva)
          struct pmap *pmap;
          register vm_offset_t sva;
          register vm_offset_t eva;
  {
          register unsigned *ptbase;
          vm_offset_t pdnxt;
          vm_offset_t ptpaddr;
          vm_offset_t sindex, eindex;
          int anyvalid;
  
          if (pmap == NULL)
                  return;
  
          if (pmap->pm_stats.resident_count == 0)
                  return;
  
          /*
           * special handling of removing one page.  a very
           * common operation and easy to short circuit some
           * code.
           */
          if ((sva + PAGE_SIZE) == eva) {
                  pmap_remove_page(pmap, sva);
                  return;
          }
  
          anyvalid = 0;
  
          /*
           * Get a local virtual address for the mappings that are being
           * worked with.
           */
          ptbase = get_ptbase(pmap);
  
          sindex = i386_btop(sva);
          eindex = i386_btop(eva);
  
          for (; sindex < eindex; sindex = pdnxt) {
  
                  /*
                   * Calculate index for next page table.
                   */
                  pdnxt = ((sindex + NPTEPG) & ~(NPTEPG - 1));
                  if (pmap->pm_stats.resident_count == 0)
                          break;
                  ptpaddr = (vm_offset_t) *pmap_pde(pmap, i386_ptob(sindex));
  
                  /*
                   * Weed out invalid mappings. Note: we assume that the page
                   * directory table is always allocated, and in kernel virtual.
                   */
                  if (ptpaddr == 0)
                          continue;
  
                  /*
                   * Limit our scan to either the end of the va represented
                   * by the current page table page, or to the end of the
                   * range being removed.
                   */
                  if (pdnxt > eindex) {
                          pdnxt = eindex;
                  }
  
                  for ( ;sindex != pdnxt; sindex++) {
                          vm_offset_t va;
                          if (ptbase[sindex] == 0) {
                                  continue;
                          }
                          va = i386_ptob(sindex);
                          
                          anyvalid++;
                          if (pmap_remove_pte(pmap,
                                  ptbase + sindex, va))
                                  break;
                  }
          }
  
          if (anyvalid) {
                  invltlb();
          }
  }
  
  /*
   *      Routine:        pmap_remove_all
   *      Function:
   *              Removes this physical page from
   *              all physical maps in which it resides.
   *              Reflects back modify bits to the pager.
   *
   *      Notes:
   *              Original versions of this routine were very
   *              inefficient because they iteratively called
   *              pmap_remove (slow...)
   */
  
  static void
  pmap_remove_all(pa)
          vm_offset_t pa;
  {
          register pv_entry_t pv;
          pv_table_t *ppv;
          register unsigned *pte, tpte;
          int nmodify;
          int update_needed;
          int s;
  
          nmodify = 0;
          update_needed = 0;
  #if defined(PMAP_DIAGNOSTIC)
          /*
           * XXX this makes pmap_page_protect(NONE) illegal for non-managed
           * pages!
           */
          if (!pmap_is_managed(pa)) {
                  panic("pmap_page_protect: illegal for unmanaged page, va: 0x%lx", pa);
          }
  #endif
  
          s = splvm();
          ppv = pa_to_pvh(pa);
          while ((pv = TAILQ_FIRST(&ppv->pv_list)) != NULL) {
                  pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
  
                  pv->pv_pmap->pm_stats.resident_count--;
  
                  tpte = *pte;
                  *pte = 0;
                  if (tpte & PG_W)
                          pv->pv_pmap->pm_stats.wired_count--;
                  /*
                   * Update the vm_page_t clean and reference bits.
                   */
                  if (tpte & PG_M) {
  #if defined(PMAP_DIAGNOSTIC)
                          if (pmap_nw_modified((pt_entry_t) tpte)) {
                                  printf("pmap_remove_all: modified page not writable: va: 0x%lx, pte: 0x%lx\n", pv->pv_va, tpte);
                          }
  #endif
                          if (pmap_track_modified(pv->pv_va))
                                  ppv->pv_vm_page->dirty = VM_PAGE_BITS_ALL;
                  }
                  if (!update_needed &&
                          ((!curproc || (&curproc->p_vmspace->vm_pmap == pv->pv_pmap)) ||
                          (pv->pv_pmap == kernel_pmap))) {
                          update_needed = 1;
                  }
  
  #if PMAP_PVLIST
                  TAILQ_REMOVE(&pv->pv_pmap->pm_pvlist, pv, pv_plist);
  #endif
                  TAILQ_REMOVE(&ppv->pv_list, pv, pv_list);
                  --ppv->pv_list_count;
                  pmap_unuse_pt(pv->pv_pmap, pv->pv_va, pv->pv_ptem);
                  free_pv_entry(pv);
          }
          ppv->pv_vm_page->flags &= ~(PG_MAPPED|PG_WRITEABLE);
  
  
          if (update_needed)
                  invltlb();
          splx(s);
          return;
  }
  
  /*
   *      Set the physical protection on the
   *      specified range of this map as requested.
   */
  void
  pmap_protect(pmap, sva, eva, prot)
          register pmap_t pmap;
          vm_offset_t sva, eva;
          vm_prot_t prot;
  {
          register unsigned *ptbase;
          vm_offset_t pdnxt;
          vm_offset_t ptpaddr;
          vm_offset_t sindex, eindex;
          int anychanged;
  
  
          if (pmap == NULL)
                  return;
  
          if ((prot & VM_PROT_READ) == VM_PROT_NONE) {
                  pmap_remove(pmap, sva, eva);
                  return;
          }
          if (prot & VM_PROT_WRITE) {
                  return;
          }
  
          anychanged = 0;
  
          ptbase = get_ptbase(pmap);
  
          sindex = i386_btop(sva);
          eindex = i386_btop(eva);
  
          for (; sindex < eindex; sindex = pdnxt) {
  
                  pdnxt = ((sindex + NPTEPG) & ~(NPTEPG - 1));
                  ptpaddr = (vm_offset_t) *pmap_pde(pmap, i386_ptob(sindex));
  
                  /*
                   * Weed out invalid mappings. Note: we assume that the page
                   * directory table is always allocated, and in kernel virtual.
                   */
                  if (ptpaddr == 0)
                          continue;
  
                  if (pdnxt > eindex) {
                          pdnxt = eindex;
                  }
  
                  for (; sindex != pdnxt; sindex++) {
  
                          unsigned pbits = ptbase[sindex];
  
                          if (pbits & PG_RW) {
                                  if (pbits & PG_M) {
                                          vm_offset_t sva = i386_ptob(sindex);
                                          if (pmap_track_modified(sva)) {
                                                  vm_page_t m = PHYS_TO_VM_PAGE(pbits);
                                                  m->dirty = VM_PAGE_BITS_ALL;
                                          }
                                  }
                                  ptbase[sindex] = pbits & ~(PG_M|PG_RW);
                                  anychanged = 1;
                          }
                  }
          }
          if (anychanged)
                  invltlb();
  }
  
  /*
   *      Insert the given physical page (p) at
   *      the specified virtual address (v) in the
   *      target physical map with the protection requested.
   *
   *      If specified, the page will be wired down, meaning
   *      that the related pte can not be reclaimed.
   *
   *      NB:  This is the only routine which MAY NOT lazy-evaluate
   *      or lose information.  That is, this routine must actually
   *      insert this page into the given map NOW.
   */
  void
  pmap_enter(pmap, va, pa, prot, wired)
          register pmap_t pmap;
          vm_offset_t va;
          register vm_offset_t pa;
          vm_prot_t prot;
          boolean_t wired;
  {
          register unsigned *pte;
          vm_offset_t opa;
          vm_offset_t origpte, newpte;
          vm_page_t mpte;
  
          if (pmap == NULL)
                  return;
  
          va &= PG_FRAME;
  #ifdef PMAP_DIAGNOSTIC
          if (va > VM_MAX_KERNEL_ADDRESS)
                  panic("pmap_enter: toobig");
          if ((va >= UPT_MIN_ADDRESS) && (va < UPT_MAX_ADDRESS))
                  panic("pmap_enter: invalid to pmap_enter page table pages (va: 0x%x)", va);
  #endif
  
          mpte = NULL;
          /*
           * In the case that a page table page is not
           * resident, we are creating it here.
           */
          if (va < UPT_MIN_ADDRESS)
                  mpte = pmap_allocpte(pmap, va);
  
          pte = pmap_pte(pmap, va);
          /*
           * Page Directory table entry not valid, we need a new PT page
           */
          if (pte == NULL) {
                  panic("pmap_enter: invalid page directory, pdir=%p, va=0x%lx\n",
                          pmap->pm_pdir[PTDPTDI], va);
          }
  
          origpte = *(vm_offset_t *)pte;
          pa &= PG_FRAME;
          opa = origpte & PG_FRAME;
  
          /*
           * Mapping has not changed, must be protection or wiring change.
           */
          if (origpte && (opa == pa)) {
                  /*
                   * Wiring change, just update stats. We don't worry about
                   * wiring PT pages as they remain resident as long as there
                   * are valid mappings in them. Hence, if a user page is wired,
                   * the PT page will be also.
                   */
                  if (wired && ((origpte & PG_W) == 0))
                          pmap->pm_stats.wired_count++;
                  else if (!wired && (origpte & PG_W))
                          pmap->pm_stats.wired_count--;
  
  #if defined(PMAP_DIAGNOSTIC)
                  if (pmap_nw_modified((pt_entry_t) origpte)) {
                          printf("pmap_enter: modified page not writable: va: 0x%lx, pte: 0x%lx\n", va, origpte);
                  }
  #endif
  
                  /*
                   * We might be turning off write access to the page,
                   * so we go ahead and sense modify status.
                   */
                  if (origpte & PG_MANAGED) {
                          vm_page_t m;
                          if (origpte & PG_M) {
                                  if (pmap_track_modified(va)) {
                                          m = PHYS_TO_VM_PAGE(pa);
                                          m->dirty = VM_PAGE_BITS_ALL;
                                  }
                          }
                          pa |= PG_MANAGED;
                  }
  
                  if (mpte)
                          --mpte->hold_count;
  
                  goto validate;
          } 
          /*
           * Mapping has changed, invalidate old range and fall through to
           * handle validating new mapping.
           */
          if (opa) {
                  int err;
                  err = pmap_remove_pte(pmap, pte, va);
                  if (err)
                          panic("pmap_enter: pte vanished, va: 0x%x", va);
          }
  
          /*
           * Enter on the PV list if part of our managed memory Note that we
           * raise IPL while manipulating pv_table since pmap_enter can be
           * called at interrupt time.
           */
          if (pmap_is_managed(pa)) {
                  pmap_insert_entry(pmap, va, mpte, pa);
                  pa |= PG_MANAGED;
          }
  
          /*
           * Increment counters
           */
          pmap->pm_stats.resident_count++;
          if (wired)
                  pmap->pm_stats.wired_count++;
  
  validate:
          /*
           * Now validate mapping with desired protection/wiring.
           */
          newpte = (vm_offset_t) (pa | pte_prot(pmap, prot) | PG_V);
  
          if (wired)
                  newpte |= PG_W;
          if (va < UPT_MIN_ADDRESS)
                  newpte |= PG_U;
          if (pmap == kernel_pmap)
                  newpte |= pgeflag;
  
          /*
           * if the mapping or permission bits are different, we need
           * to update the pte.
           */
          if ((origpte & ~(PG_M|PG_A)) != newpte) {
                  *pte = newpte;
                  if (origpte)
                          invltlb_1pg(va);
          }
  }
  
  /*
   * this code makes some *MAJOR* assumptions:
   * 1. Current pmap & pmap exists.
   * 2. Not wired.
   * 3. Read access.
   * 4. No page table pages.
   * 5. Tlbflush is deferred to calling procedure.
   * 6. Page IS managed.
   * but is *MUCH* faster than pmap_enter...
   */
  
  static vm_page_t
  pmap_enter_quick(pmap, va, pa, mpte)
          register pmap_t pmap;
          vm_offset_t va;
          register vm_offset_t pa;
          vm_page_t mpte;
  {
          register unsigned *pte;
  
          /*
           * In the case that a page table page is not
           * resident, we are creating it here.
           */
          if (va < UPT_MIN_ADDRESS) {
                  unsigned ptepindex;
                  vm_offset_t ptepa;
  
                  /*
                   * Calculate pagetable page index
                   */
                  ptepindex = va >> PDRSHIFT;
                  if (mpte && (mpte->pindex == ptepindex)) {
                          ++mpte->hold_count;
                  } else {
  retry:
                          /*
                           * Get the page directory entry
                           */
                          ptepa = (vm_offset_t) pmap->pm_pdir[ptepindex];
  
                          /*
                           * If the page table page is mapped, we just increment
                           * the hold count, and activate it.
                           */
                          if (ptepa) {
  #if defined(PTPHINT)
                                  if (pmap->pm_ptphint &&
                                          (pmap->pm_ptphint->pindex == ptepindex)) {
                                          mpte = pmap->pm_ptphint;
                                  } else {
                                          mpte = pmap_page_lookup( pmap->pm_pteobj, ptepindex);
                                          pmap->pm_ptphint = mpte;
                                  }
  #else
                                  mpte = pmap_page_lookup( pmap->pm_pteobj, ptepindex);
  #endif
                                  if (mpte == NULL)
                                          goto retry;
                                  ++mpte->hold_count;
                          } else {
                                  mpte = _pmap_allocpte(pmap, ptepindex);
                          }
                  }
          } else {
                  mpte = NULL;
          }
  
          /*
           * This call to vtopte makes the assumption that we are
           * entering the page into the current pmap.  In order to support
           * quick entry into any pmap, one would likely use pmap_pte_quick.
           * But that isn't as quick as vtopte.
           */
          pte = (unsigned *)vtopte(va);
          if (*pte) {
                  if (mpte)
                          pmap_unwire_pte_hold(pmap, mpte);
                  return 0;
          }
  
          /*
           * Enter on the PV list if part of our managed memory Note that we
           * raise IPL while manipulating pv_table since pmap_enter can be
           * called at interrupt time.
           */
          pmap_insert_entry(pmap, va, mpte, pa);
  
          /*
           * Increment counters
           */
          pmap->pm_stats.resident_count++;
  
          /*
           * Now validate mapping with RO protection
           */
          *pte = pa | PG_V | PG_U | PG_MANAGED;
  
          return mpte;
  }
  
  #define MAX_INIT_PT (96)
  /*
   * pmap_object_init_pt preloads the ptes for a given object
   * into the specified pmap.  This eliminates the blast of soft
   * faults on process startup and immediately after an mmap.
   */
  void
  pmap_object_init_pt(pmap, addr, object, pindex, size, limit)
          pmap_t pmap;
          vm_offset_t addr;
          vm_object_t object;
          vm_pindex_t pindex;
          vm_size_t size;
          int limit;
  {
          vm_offset_t tmpidx;
          int psize;
          vm_page_t p, mpte;
          int objpgs;
  
          psize = i386_btop(size);
  
          if (!pmap || (object->type != OBJT_VNODE) ||
                  (limit && (psize > MAX_INIT_PT) &&
                          (object->resident_page_count > MAX_INIT_PT))) {
                  return;
          }
  
          if (psize + pindex > object->size)
                  psize = object->size - pindex;
  
          mpte = NULL;
          /*
           * if we are processing a major portion of the object, then scan the
           * entire thing.
           */
          if (psize > (object->size >> 2)) {
                  objpgs = psize;
  
                  for (p = TAILQ_FIRST(&object->memq);
                      ((objpgs > 0) && (p != NULL));
                      p = TAILQ_NEXT(p, listq)) {
  
                          tmpidx = p->pindex;
                          if (tmpidx < pindex) {
                                  continue;
                          }
                          tmpidx -= pindex;
                          if (tmpidx >= psize) {
                                  continue;
                          }
                          if (((p->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
                              (p->busy == 0) &&
                              (p->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
                                  if ((p->queue - p->pc) == PQ_CACHE)
                                          vm_page_deactivate(p);
                                  p->flags |= PG_BUSY;
                                  mpte = pmap_enter_quick(pmap, 
                                          addr + i386_ptob(tmpidx),
                                          VM_PAGE_TO_PHYS(p), mpte);
                                  p->flags |= PG_MAPPED;
                                  PAGE_WAKEUP(p);
                          }
                          objpgs -= 1;
                  }
          } else {
                  /*
                   * else lookup the pages one-by-one.
                   */
                  for (tmpidx = 0; tmpidx < psize; tmpidx += 1) {
                          p = vm_page_lookup(object, tmpidx + pindex);
                          if (p &&
                              ((p->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
                              (p->busy == 0) &&
                              (p->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
                                  if ((p->queue - p->pc) == PQ_CACHE)
                                          vm_page_deactivate(p);
                                  p->flags |= PG_BUSY;
                                  mpte = pmap_enter_quick(pmap, 
                                          addr + i386_ptob(tmpidx),
                                          VM_PAGE_TO_PHYS(p), mpte);
                                  p->flags |= PG_MAPPED;
                                  PAGE_WAKEUP(p);
                          }
                  }
          }
          return;
  }
  
  /*
   * pmap_prefault provides a quick way of clustering
   * pagefaults into a processes address space.  It is a "cousin"
   * of pmap_object_init_pt, except it runs at page fault time instead
   * of mmap time.
   */
  #define PFBAK 2
  #define PFFOR 2
  #define PAGEORDER_SIZE (PFBAK+PFFOR)
  
  static int pmap_prefault_pageorder[] = {
          -PAGE_SIZE, PAGE_SIZE, -2 * PAGE_SIZE, 2 * PAGE_SIZE
  };
  
  void
  pmap_prefault(pmap, addra, entry, object)
          pmap_t pmap;
          vm_offset_t addra;
          vm_map_entry_t entry;
          vm_object_t object;
  {
          int i;
          vm_offset_t starta;
          vm_offset_t addr;
          vm_pindex_t pindex;
          vm_page_t m, mpte;
  
          if (entry->object.vm_object != object)
                  return;
  
          if (!curproc || (pmap != &curproc->p_vmspace->vm_pmap))
                  return;
  
          starta = addra - PFBAK * PAGE_SIZE;
          if (starta < entry->start) {
                  starta = entry->start;
          } else if (starta > addra) {
                  starta = 0;
          }
  
          mpte = NULL;
          for (i = 0; i < PAGEORDER_SIZE; i++) {
                  vm_object_t lobject;
                  unsigned *pte;
  
                  addr = addra + pmap_prefault_pageorder[i];
                  if (addr < starta || addr >= entry->end)
                          continue;
  
                  if ((*pmap_pde(pmap, addr)) == NULL) 
                          continue;
  
                  pte = (unsigned *) vtopte(addr);
                  if (*pte)
                          continue;
  
                  pindex = ((addr - entry->start) + entry->offset) >> PAGE_SHIFT;
                  lobject = object;
                  for (m = vm_page_lookup(lobject, pindex);
                      (!m && (lobject->type == OBJT_DEFAULT) && (lobject->backing_object));
                      lobject = lobject->backing_object) {
                          if (lobject->backing_object_offset & PAGE_MASK)
                                  break;
                          pindex += (lobject->backing_object_offset >> PAGE_SHIFT);
                          m = vm_page_lookup(lobject->backing_object, pindex);
                  }
  
                  /*
                   * give-up when a page is not in memory
                   */
                  if (m == NULL)
                          break;
  
                  if (((m->valid & VM_PAGE_BITS_ALL) == VM_PAGE_BITS_ALL) &&
                      (m->busy == 0) &&
                      (m->flags & (PG_BUSY | PG_FICTITIOUS)) == 0) {
  
                          if ((m->queue - m->pc) == PQ_CACHE) {
                                  vm_page_deactivate(m);
                          }
                          m->flags |= PG_BUSY;
                          mpte = pmap_enter_quick(pmap, addr,
                                  VM_PAGE_TO_PHYS(m), mpte);
                          m->flags |= PG_MAPPED;
                          PAGE_WAKEUP(m);
                  }
          }
  }
  
  /*
   *      Routine:        pmap_change_wiring
   *      Function:       Change the wiring attribute for a map/virtual-address
   *                      pair.
   *      In/out conditions:
   *                      The mapping must already exist in the pmap.
   */
  void
  pmap_change_wiring(pmap, va, wired)
          register pmap_t pmap;
          vm_offset_t va;
          boolean_t wired;
  {
          register unsigned *pte;
  
          if (pmap == NULL)
                  return;
  
          pte = pmap_pte(pmap, va);
  
          if (wired && !pmap_pte_w(pte))
                  pmap->pm_stats.wired_count++;
          else if (!wired && pmap_pte_w(pte))
                  pmap->pm_stats.wired_count--;
  
          /*
           * Wiring is not a hardware characteristic so there is no need to
           * invalidate TLB.
           */
          pmap_pte_set_w(pte, wired);
  }
  
  
  
  /*
   *      Copy the range specified by src_addr/len
   *      from the source map to the range dst_addr/len
   *      in the destination map.
   *
   *      This routine is only advisory and need not do anything.
   */
  
  void
  pmap_copy(dst_pmap, src_pmap, dst_addr, len, src_addr)
          pmap_t dst_pmap, src_pmap;
          vm_offset_t dst_addr;
          vm_size_t len;
          vm_offset_t src_addr;
  {
          vm_offset_t addr;
          vm_offset_t end_addr = src_addr + len;
          vm_offset_t pdnxt;
          unsigned src_frame, dst_frame;
  
          if (dst_addr != src_addr)
                  return;
  
          src_frame = ((unsigned) src_pmap->pm_pdir[PTDPTDI]) & PG_FRAME;
          if (src_frame != (((unsigned) PTDpde) & PG_FRAME)) {
                  return;
          }
  
          dst_frame = ((unsigned) dst_pmap->pm_pdir[PTDPTDI]) & PG_FRAME;
          if (dst_frame != (((unsigned) APTDpde) & PG_FRAME)) {
                  APTDpde = (pd_entry_t) (dst_frame | PG_RW | PG_V);
                  invltlb();
          }
  
          for(addr = src_addr; addr < end_addr; addr = pdnxt) {
                  unsigned *src_pte, *dst_pte;
                  vm_page_t dstmpte, srcmpte;
                  vm_offset_t srcptepaddr;
                  unsigned ptepindex;
  
                  if (addr >= UPT_MIN_ADDRESS)
                          panic("pmap_copy: invalid to pmap_copy page tables\n");
  
                  pdnxt = ((addr + PAGE_SIZE*NPTEPG) & ~(PAGE_SIZE*NPTEPG - 1));
                  ptepindex = addr >> PDRSHIFT;
  
                  srcptepaddr = (vm_offset_t) src_pmap->pm_pdir[ptepindex];
                  if (srcptepaddr == 0)
                          continue;
  
                  srcmpte = vm_page_lookup(src_pmap->pm_pteobj, ptepindex);
                  if ((srcmpte->hold_count == 0) || (srcmpte->flags & PG_BUSY))
                          continue;
  
                  if (pdnxt > end_addr)
                          pdnxt = end_addr;
  
                  src_pte = (unsigned *) vtopte(addr);
                  dst_pte = (unsigned *) avtopte(addr);
                  while (addr < pdnxt) {
                          unsigned ptetemp;
                          ptetemp = *src_pte;
                          /*
                           * we only virtual copy managed pages
                           */
                          if ((ptetemp & PG_MANAGED) != 0) {
                                  /*
                                   * We have to check after allocpte for the
                                   * pte still being around...  allocpte can
                                   * block.
                                   */
                                  dstmpte = pmap_allocpte(dst_pmap, addr);
                                  if ((*dst_pte == 0) && (ptetemp = *src_pte)) {
                                          /*
                                           * Clear the modified and
                                           * accessed (referenced) bits
                                           * during the copy.
                                           */
                                          *dst_pte = ptetemp & ~(PG_M|PG_A);
                                          dst_pmap->pm_stats.resident_count++;
                                          pmap_insert_entry(dst_pmap, addr,
                                                  dstmpte,
                                                  (ptetemp & PG_FRAME));
                                  } else {
                                          pmap_unwire_pte_hold(dst_pmap, dstmpte);
                                  }
                                  if (dstmpte->hold_count >= srcmpte->hold_count)
                                          break;
                          }
                          addr += PAGE_SIZE;
                          ++src_pte;
                          ++dst_pte;
                  }
          }
  }       
  
  /*
   *      Routine:        pmap_kernel
   *      Function:
   *              Returns the physical map handle for the kernel.
   */
  pmap_t
  pmap_kernel()
  {
          return (kernel_pmap);
  }
  
  /*
   *      pmap_zero_page zeros the specified (machine independent)
   *      page by mapping the page into virtual memory and using
   *      bzero to clear its contents, one machine dependent page
   *      at a time.
   */
  void
  pmap_zero_page(phys)
          vm_offset_t phys;
  {
          if (*(int *) CMAP2)
                  panic("pmap_zero_page: CMAP busy");
  
          *(int *) CMAP2 = PG_V | PG_RW | (phys & PG_FRAME);
          bzero(CADDR2, PAGE_SIZE);
          *(int *) CMAP2 = 0;
          invltlb_1pg((vm_offset_t) CADDR2);
  }
  
  /*
   *      pmap_copy_page copies the specified (machine independent)
   *      page by mapping the page into virtual memory and using
   *      bcopy to copy the page, one machine dependent page at a
   *      time.
   */
  void
  pmap_copy_page(src, dst)
          vm_offset_t src;
          vm_offset_t dst;
  {
          if (*(int *) CMAP1 || *(int *) CMAP2)
                  panic("pmap_copy_page: CMAP busy");
  
          *(int *) CMAP1 = PG_V | PG_RW | (src & PG_FRAME);
          *(int *) CMAP2 = PG_V | PG_RW | (dst & PG_FRAME);
  
          bcopy(CADDR1, CADDR2, PAGE_SIZE);
  
          *(int *) CMAP1 = 0;
          *(int *) CMAP2 = 0;
          invltlb_2pg( (vm_offset_t) CADDR1, (vm_offset_t) CADDR2);
  }
  
  
  /*
   *      Routine:        pmap_pageable
   *      Function:
   *              Make the specified pages (by pmap, offset)
   *              pageable (or not) as requested.
   *
   *              A page which is not pageable may not take
   *              a fault; therefore, its page table entry
   *              must remain valid for the duration.
   *
   *              This routine is merely advisory; pmap_enter
   *              will specify that these pages are to be wired
   *              down (or not) as appropriate.
   */
  void
  pmap_pageable(pmap, sva, eva, pageable)
          pmap_t pmap;
          vm_offset_t sva, eva;
          boolean_t pageable;
  {
  }
  
  /*
   * this routine returns true if a physical page resides
   * in the given pmap.
   */
  boolean_t
  pmap_page_exists(pmap, pa)
          pmap_t pmap;
          vm_offset_t pa;
  {
          register pv_entry_t pv;
          pv_table_t *ppv;
          int s;
  
          if (!pmap_is_managed(pa))
                  return FALSE;
  
          s = splvm();
  
          ppv = pa_to_pvh(pa);
          /*
           * Not found, check current mappings returning immediately if found.
           */
          for (pv = TAILQ_FIRST(&ppv->pv_list);
                  pv;
                  pv = TAILQ_NEXT(pv, pv_list)) {
                  if (pv->pv_pmap == pmap) {
                          splx(s);
                          return TRUE;
                  }
          }
          splx(s);
          return (FALSE);
  }
  
  #define PMAP_REMOVE_PAGES_CURPROC_ONLY
  /*
   * Remove all pages from specified address space
   * this aids process exit speeds.  Also, this code
   * is special cased for current process only, but
   * can have the more generic (and slightly slower)
   * mode enabled.  This is much faster than pmap_remove
   * in the case of running down an entire address space.
   */
  void
  pmap_remove_pages(pmap, sva, eva)
          pmap_t pmap;
          vm_offset_t sva, eva;
  {
          unsigned *pte, tpte;
          pv_table_t *ppv;
          pv_entry_t pv, npv;
          int s;
  
  #if PMAP_PVLIST
  
  #ifdef PMAP_REMOVE_PAGES_CURPROC_ONLY
          if (!curproc || (pmap != &curproc->p_vmspace->vm_pmap)) {
                  printf("warning: pmap_remove_pages called with non-current pmap\n");
                  return;
          }
  #endif
  
          s = splvm();
          for(pv = TAILQ_FIRST(&pmap->pm_pvlist);
                  pv;
                  pv = npv) {
  
                  if (pv->pv_va >= eva || pv->pv_va < sva) {
                          npv = TAILQ_NEXT(pv, pv_plist);
                          continue;
                  }
  
  #ifdef PMAP_REMOVE_PAGES_CURPROC_ONLY
                  pte = (unsigned *)vtopte(pv->pv_va);
  #else
                  pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
  #endif
                  tpte = *pte;
  
  /*
   * We cannot remove wired pages from a process' mapping at this time
   */
                  if (tpte & PG_W) {
                          npv = TAILQ_NEXT(pv, pv_plist);
                          continue;
                  }
                  *pte = 0;
  
                  ppv = pa_to_pvh(tpte);
  
                  pv->pv_pmap->pm_stats.resident_count--;
  
                  /*
                   * Update the vm_page_t clean and reference bits.
                   */
                  if (tpte & PG_M) {
                          ppv->pv_vm_page->dirty = VM_PAGE_BITS_ALL;
                  }
  
  
                  npv = TAILQ_NEXT(pv, pv_plist);
                  TAILQ_REMOVE(&pv->pv_pmap->pm_pvlist, pv, pv_plist);
  
                  --ppv->pv_list_count;
                  TAILQ_REMOVE(&ppv->pv_list, pv, pv_list);
                  if (TAILQ_FIRST(&ppv->pv_list) == NULL) {
                          ppv->pv_vm_page->flags &= ~(PG_MAPPED|PG_WRITEABLE);
                  }
  
                  pmap_unuse_pt(pv->pv_pmap, pv->pv_va, pv->pv_ptem);
                  free_pv_entry(pv);
          }
          splx(s);
          invltlb();
  #endif
  }
  
  /*
   * pmap_testbit tests bits in pte's
   * note that the testbit/changebit routines are inline,
   * and a lot of things compile-time evaluate.
   */
  static boolean_t
  pmap_testbit(pa, bit)
          register vm_offset_t pa;
          int bit;
  {
          register pv_entry_t pv;
          pv_table_t *ppv;
          unsigned *pte;
          int s;
  
          if (!pmap_is_managed(pa))
                  return FALSE;
  
          ppv = pa_to_pvh(pa);
          if (TAILQ_FIRST(&ppv->pv_list) == NULL)
                  return FALSE;
  
          s = splvm();
  
          for (pv = TAILQ_FIRST(&ppv->pv_list);
                  pv;
                  pv = TAILQ_NEXT(pv, pv_list)) {
  
                  /*
                   * if the bit being tested is the modified bit, then
                   * mark clean_map and ptes as never
                   * modified.
                   */
                  if (bit & (PG_A|PG_M)) {
                          if (!pmap_track_modified(pv->pv_va))
                                  continue;
                  }
  
  #if defined(PMAP_DIAGNOSTIC)
                  if (!pv->pv_pmap) {
                          printf("Null pmap (tb) at va: 0x%lx\n", pv->pv_va);
                          continue;
                  }
  #endif
                  pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
                  if (*pte & bit) {
                          splx(s);
                          return TRUE;
                  }
          }
          splx(s);
          return (FALSE);
  }
  
  /*
   * this routine is used to modify bits in ptes
   */
  static void
  pmap_changebit(pa, bit, setem)
          vm_offset_t pa;
          int bit;
          boolean_t setem;
  {
          register pv_entry_t pv;
          pv_table_t *ppv;
          register unsigned *pte;
          int changed;
          int s;
  
          if (!pmap_is_managed(pa))
                  return;
  
          s = splvm();
          changed = 0;
          ppv = pa_to_pvh(pa);
  
          /*
           * Loop over all current mappings setting/clearing as appropos If
           * setting RO do we need to clear the VAC?
           */
          for (pv = TAILQ_FIRST(&ppv->pv_list);
                  pv;
                  pv = TAILQ_NEXT(pv, pv_list)) {
  
                  /*
                   * don't write protect pager mappings
                   */
                  if (!setem && (bit == PG_RW)) {
                          if (!pmap_track_modified(pv->pv_va))
                                  continue;
                  }
  
  #if defined(PMAP_DIAGNOSTIC)
                  if (!pv->pv_pmap) {
                          printf("Null pmap (cb) at va: 0x%lx\n", pv->pv_va);
                          continue;
                  }
  #endif
  
                  pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
  
                  if (setem) {
                          *(int *)pte |= bit;
                          changed = 1;
                  } else {
                          vm_offset_t pbits = *(vm_offset_t *)pte;
                          if (pbits & bit) {
                                  changed = 1;
                                  if (bit == PG_RW) {
                                          if (pbits & PG_M) {
                                                  ppv->pv_vm_page->dirty = VM_PAGE_BITS_ALL;
                                          }
                                          *(int *)pte = pbits & ~(PG_M|PG_RW);
                                  } else {
                                          *(int *)pte = pbits & ~bit;
                                  }
                          }
                  }
          }
          splx(s);
          if (changed)
                  invltlb();
  }
  
  /*
   *      pmap_page_protect:
   *
   *      Lower the permission for all mappings to a given page.
   */
  void
  pmap_page_protect(phys, prot)
          vm_offset_t phys;
          vm_prot_t prot;
  {
          if ((prot & VM_PROT_WRITE) == 0) {
                  if (prot & (VM_PROT_READ | VM_PROT_EXECUTE)) {
                          pmap_changebit(phys, PG_RW, FALSE);
                  } else {
                          pmap_remove_all(phys);
                  }
          }
  }
  
  vm_offset_t
  pmap_phys_address(ppn)
          int ppn;
  {
          return (i386_ptob(ppn));
  }
  
  /*
   *      pmap_is_referenced:
   *
   *      Return whether or not the specified physical page was referenced
   *      by any physical maps.
   */
  boolean_t
  pmap_is_referenced(vm_offset_t pa)
  {
          register pv_entry_t pv;
          pv_table_t *ppv;
          unsigned *pte;
          int s;
  
          if (!pmap_is_managed(pa))
                  return FALSE;
  
          ppv = pa_to_pvh(pa);
  
          s = splvm();
          /*
           * Not found, check current mappings returning immediately if found.
           */
          for (pv = TAILQ_FIRST(&ppv->pv_list);
                  pv;
                  pv = TAILQ_NEXT(pv, pv_list)) {
  
                  /*
                   * if the bit being tested is the modified bit, then
                   * mark clean_map and ptes as never
                   * modified.
                   */
                  if (!pmap_track_modified(pv->pv_va))
                          continue;
  
                  pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
                  if ((int) *pte & PG_A) {
                          splx(s);
                          return TRUE;
                  }
          }
          splx(s);
          return (FALSE);
  }
  
  /*
   *      pmap_ts_referenced:
   *
   *      Return the count of reference bits for a page, clearing all of them.
   *      
   */
  int
  pmap_ts_referenced(vm_offset_t pa)
  {
          register pv_entry_t pv;
          pv_table_t *ppv;
          unsigned *pte;
          int s;
          int rtval = 0;
  
          if (!pmap_is_managed(pa))
                  return FALSE;
  
          s = splvm();
  
          ppv = pa_to_pvh(pa);
  
          if (TAILQ_FIRST(&ppv->pv_list) == NULL) {
                  splx(s);
                  return 0;
          }
                  
          /*
           * Not found, check current mappings returning immediately if found.
           */
          for (pv = TAILQ_FIRST(&ppv->pv_list);
                  pv;
                  pv = TAILQ_NEXT(pv, pv_list)) {
                  /*
                   * if the bit being tested is the modified bit, then
                   * mark clean_map and ptes as never
                   * modified.
                   */
                  if (!pmap_track_modified(pv->pv_va))
                          continue;
  
                  pte = pmap_pte_quick(pv->pv_pmap, pv->pv_va);
                  if (pte == NULL) {
                          continue;
                  }
                  if (*pte & PG_A) {
                          rtval++;
                          *pte &= ~PG_A;
                  }
          }
          splx(s);
          if (rtval) {
                  invltlb();
          }
          return (rtval);
  }
  
  /*
   *      pmap_is_modified:
   *
   *      Return whether or not the specified physical page was modified
   *      in any physical maps.
   */
  boolean_t
  pmap_is_modified(vm_offset_t pa)
  {
          return pmap_testbit((pa), PG_M);
  }
  
  /*
   *      Clear the modify bits on the specified physical page.
   */
  void
  pmap_clear_modify(vm_offset_t pa)
  {
          pmap_changebit((pa), PG_M, FALSE);
  }
  
  /*
   *      pmap_clear_reference:
   *
   *      Clear the reference bit on the specified physical page.
   */
  void
  pmap_clear_reference(vm_offset_t pa)
  {
          pmap_changebit((pa), PG_A, FALSE);
  }
  
  /*
   * Miscellaneous support routines follow
   */
  
  static void
  i386_protection_init()
  {
          register int *kp, prot;
  
          kp = protection_codes;
          for (prot = 0; prot < 8; prot++) {
                  switch (prot) {
                  case VM_PROT_NONE | VM_PROT_NONE | VM_PROT_NONE:
                          /*
                           * Read access is also 0. There isn't any execute bit,
                           * so just make it readable.
                           */
                  case VM_PROT_READ | VM_PROT_NONE | VM_PROT_NONE:
                  case VM_PROT_READ | VM_PROT_NONE | VM_PROT_EXECUTE:
                  case VM_PROT_NONE | VM_PROT_NONE | VM_PROT_EXECUTE:
                          *kp++ = 0;
                          break;
                  case VM_PROT_NONE | VM_PROT_WRITE | VM_PROT_NONE:
                  case VM_PROT_NONE | VM_PROT_WRITE | VM_PROT_EXECUTE:
                  case VM_PROT_READ | VM_PROT_WRITE | VM_PROT_NONE:
                  case VM_PROT_READ | VM_PROT_WRITE | VM_PROT_EXECUTE:
                          *kp++ = PG_RW;
                          break;
                  }
          }
  }
  
  /*
   * Map a set of physical memory pages into the kernel virtual
   * address space. Return a pointer to where it is mapped. This
   * routine is intended to be used for mapping device memory,
   * NOT real memory. The non-cacheable bits are set on each
   * mapped page.
   */
  void *
  pmap_mapdev(pa, size)
          vm_offset_t pa;
          vm_size_t size;
  {
          vm_offset_t va, tmpva;
          unsigned *pte;
  
          size = roundup(size, PAGE_SIZE);
  
          va = kmem_alloc_pageable(kernel_map, size);
          if (!va)
                  panic("pmap_mapdev: Couldn't alloc kernel virtual memory");
  
          pa = pa & PG_FRAME;
          for (tmpva = va; size > 0;) {
                  pte = (unsigned *)vtopte(tmpva);
                  *pte = pa | PG_RW | PG_V;
                  size -= PAGE_SIZE;
                  tmpva += PAGE_SIZE;
                  pa += PAGE_SIZE;
          }
          invltlb();
  
          return ((void *) va);
  }
  
  /*
   * perform the pmap work for mincore
   */
  int
  pmap_mincore(pmap, addr)
          pmap_t pmap;
          vm_offset_t addr;
  {
          
          unsigned *ptep, pte;
          int val = 0;
          
          ptep = pmap_pte(pmap, addr);
          if (ptep == 0) {
                  return 0;
          }
  
          if (pte = *ptep) {
                  vm_offset_t pa;
                  val = MINCORE_INCORE;
                  pa = pte & PG_FRAME;
  
                  /*
                   * Modified by us
                   */
                  if (pte & PG_M)
                          val |= MINCORE_MODIFIED|MINCORE_MODIFIED_OTHER;
                  /*
                   * Modified by someone
                   */
                  else if (PHYS_TO_VM_PAGE(pa)->dirty ||
                          pmap_is_modified(pa))
                          val |= MINCORE_MODIFIED_OTHER;
                  /*
                   * Referenced by us
                   */
                  if (pte & PG_U)
                          val |= MINCORE_REFERENCED|MINCORE_REFERENCED_OTHER;
  
                  /*
                   * Referenced by someone
                   */
                  else if ((PHYS_TO_VM_PAGE(pa)->flags & PG_REFERENCED) ||
                          pmap_is_referenced(pa))
                          val |= MINCORE_REFERENCED_OTHER;
          } 
          return val;
  }
  
  #if defined(PMAP_DEBUG)
  pmap_pid_dump(int pid) {
          pmap_t pmap;
          struct proc *p;
          int npte = 0;
          int index;
          for (p = allproc.lh_first; p != NULL; p = p->p_list.le_next) {
                  if (p->p_pid != pid)
                          continue;
  
                  if (p->p_vmspace) {
                          int i,j;
                          index = 0;
                          pmap = &p->p_vmspace->vm_pmap;
                          for(i=0;i<1024;i++) {
                                  pd_entry_t *pde;
                                  unsigned *pte;
                                  unsigned base = i << PDRSHIFT;
                                  
                                  pde = &pmap->pm_pdir[i];
                                  if (pde && pmap_pde_v(pde)) {
                                          for(j=0;j<1024;j++) {
                                                  unsigned va = base + (j << PAGE_SHIFT);
                                                  if (va >= (vm_offset_t) VM_MIN_KERNEL_ADDRESS) {
                                                          if (index) {
                                                                  index = 0;
                                                                  printf("\n");
                                                          }
                                                          return npte;
                                                  }
                                                  pte = pmap_pte_quick( pmap, va);
                                                  if (pte && pmap_pte_v(pte)) {
                                                          vm_offset_t pa;
                                                          vm_page_t m;
                                                          pa = *(int *)pte;
                                                          m = PHYS_TO_VM_PAGE((pa & PG_FRAME));
                                                          printf("va: 0x%x, pt: 0x%x, h: %d, w: %d, f: 0x%x",
                                                                  va, pa, m->hold_count, m->wire_count, m->flags);
                                                          npte++;
                                                          index++;
                                                          if (index >= 2) {
                                                                  index = 0;
                                                                  printf("\n");
                                                          } else {
                                                                  printf(" ");
                                                          }
                                                  }
                                          }
                                  }
                          }
                  }
          }
          return npte;
  }
  #endif
  
  #if defined(DEBUG)
  
  static void     pads __P((pmap_t pm));
  static void     pmap_pvdump __P((vm_offset_t pa));
  
  /* print address space of pmap*/
  static void
  pads(pm)
          pmap_t pm;
  {
          unsigned va, i, j;
          unsigned *ptep;
  
          if (pm == kernel_pmap)
                  return;
          for (i = 0; i < 1024; i++)
                  if (pm->pm_pdir[i])
                          for (j = 0; j < 1024; j++) {
                                  va = (i << PDRSHIFT) + (j << PAGE_SHIFT);
                                  if (pm == kernel_pmap && va < KERNBASE)
                                          continue;
                                  if (pm != kernel_pmap && va > UPT_MAX_ADDRESS)
                                          continue;
                                  ptep = pmap_pte_quick(pm, va);
                                  if (pmap_pte_v(ptep))
                                          printf("%x:%x ", va, *(int *) ptep);
                          };
  
  }
  
  static void
  pmap_pvdump(pa)
          vm_offset_t pa;
  {
          pv_table_t *ppv;
          register pv_entry_t pv;
  
          printf("pa %x", pa);
          ppv = pa_to_pvh(pa);
          for (pv = TAILQ_FIRST(&ppv->pv_list);
                  pv;
                  pv = TAILQ_NEXT(pv, pv_list)) {
  #ifdef used_to_be
                  printf(" -> pmap %x, va %x, flags %x",
                      pv->pv_pmap, pv->pv_va, pv->pv_flags);
  #endif
                  printf(" -> pmap %x, va %x",
                      pv->pv_pmap, pv->pv_va);
                  pads(pv->pv_pmap);
          }
          printf(" ");
  }
  #endif