diff --git a/mps/code/arenavm.c b/mps/code/arenavm.c
index 743e17acb09..34fb5427982 100644
--- a/mps/code/arenavm.c
+++ b/mps/code/arenavm.c
@@ -22,13 +22,14 @@
  */
 
 #include "boot.h"
-#include "tract.h"
 #include "bt.h"
-#include "sa.h"
+#include "cbs.h"
 #include "mpm.h"
 #include "mpsavm.h"
-#include "cbs.h"
 #include "poolmfs.h"
+#include "sa.h"
+#include "tract.h"
+#include "vm.h"
 
 SRCID(arenavm, "$Id$");
 
@@ -41,13 +42,14 @@ typedef struct VMChunkStruct *VMChunk;
 
 typedef struct VMChunkStruct {
   ChunkStruct chunkStruct;      /* generic chunk */
-  VM vm;                        /* virtual memory handle */
+  VMStruct vmStruct;            /* virtual memory descriptor */
   Addr overheadMappedLimit;     /* limit of pages mapped for overhead */
   SparseArrayStruct pages;      /* to manage backing store of page table */
   Sig sig;                      /* <design/sig/> */
 } VMChunkStruct;
 
 #define VMChunk2Chunk(vmchunk) (&(vmchunk)->chunkStruct)
+#define VMChunkVM(vmchunk) (&(vmchunk)->vmStruct)
 #define Chunk2VMChunk(chunk) PARENT(VMChunkStruct, chunkStruct, chunk)
 
 
@@ -68,9 +70,9 @@ typedef struct VMArenaStruct *VMArena;
 
 typedef struct VMArenaStruct {  /* VM arena structure */
   ArenaStruct arenaStruct;
-  VM vm;                        /* VM where the arena itself is stored */
+  VMStruct vmStruct;            /* VM descriptor for VM containing arena */
   char vmParams[VMParamSize];   /* VM parameter block */
-  Size spareSize;              /* total size of spare pages */
+  Size spareSize;               /* total size of spare pages */
   Size extendBy;                /* desired arena increment */
   Size extendMin;               /* minimum arena increment */
   ArenaVMExtendedCallback extended;
@@ -81,6 +83,7 @@ typedef struct VMArenaStruct {  /* VM arena structure */
 
 #define Arena2VMArena(arena) PARENT(VMArenaStruct, arenaStruct, arena)
 #define VMArena2Arena(vmarena) (&(vmarena)->arenaStruct)
+#define VMArenaVM(vmarena) (&(vmarena)->vmStruct)
 
 
 /* Forward declarations */
@@ -101,7 +104,7 @@ static Bool VMChunkCheck(VMChunk vmchunk)
   CHECKS(VMChunk, vmchunk);
   chunk = VMChunk2Chunk(vmchunk);
   CHECKD(Chunk, chunk);
-  CHECKD_NOSIG(VM, vmchunk->vm); /* <design/check/#hidden-type> */
+  CHECKD(VM, VMChunkVM(vmchunk));
   CHECKL(SizeIsAligned(ChunkPageSize(chunk), VMPageSize()));
   CHECKL(vmchunk->overheadMappedLimit <= (Addr)chunk->pageTable);
   CHECKD(SparseArray, &vmchunk->pages);
@@ -173,7 +176,7 @@ static Bool VMArenaCheck(VMArena vmArena)
     CHECKD(VMChunk, primary);
     /* We could iterate over all chunks accumulating an accurate */
     /* count of committed, but we don't have all day. */
-    CHECKL(VMMapped(primary->vm) <= arena->committed);
+    CHECKL(VMMapped(VMChunkVM(primary)) <= arena->committed);
   }
   
   CHECKD_NOSIG(Ring, &vmArena->spareRing);
@@ -279,7 +282,8 @@ static Res VMChunkCreate(Chunk *chunkReturn, VMArena vmArena, Size size,
 {
   Res res;
   Addr base, limit, chunkStructLimit;
-  VM vm;
+  VMStruct vmStruct;
+  VM vm = &vmStruct;
   BootBlockStruct bootStruct;
   BootBlock boot = &bootStruct;
   VMChunk vmChunk;
@@ -290,7 +294,8 @@ static Res VMChunkCreate(Chunk *chunkReturn, VMArena vmArena, Size size,
   AVER(size > 0);
   AVERT(ArenaGrainSize, grainSize);
 
-  res = VMCreate(&vm, size, grainSize, vmArena->vmParams);
+  /* Store VM descriptor on the stack until we have a chunk to put it in. */
+  res = VMCreate(vm, size, grainSize, vmArena->vmParams);
   if (res != ResOK)
     goto failVMCreate;
 
@@ -314,7 +319,8 @@ static Res VMChunkCreate(Chunk *chunkReturn, VMArena vmArena, Size size,
     goto failChunkMap;
   vmChunk->overheadMappedLimit = chunkStructLimit;
 
-  vmChunk->vm = vm;
+  /* Copy VM descriptor into its place in the chunk. */
+  (void)mps_lib_memcpy(VMChunkVM(vmChunk), vm, sizeof vmStruct);
   res = ChunkInit(VMChunk2Chunk(vmChunk), VMArena2Arena(vmArena),
                   base, limit, grainSize, boot);
   if (res != ResOK)
@@ -329,7 +335,7 @@ static Res VMChunkCreate(Chunk *chunkReturn, VMArena vmArena, Size size,
   return ResOK;
 
 failChunkInit:
-  /* No need to unmap, as we're destroying the VM. */
+  VMUnmap(vm, VMBase(vm), chunkStructLimit);
 failChunkMap:
 failChunkAlloc:
 failBootInit:
@@ -375,7 +381,7 @@ static Res VMChunkInit(Chunk chunk, BootBlock boot)
   /* Map memory for the bit tables. */
   if (vmChunk->overheadMappedLimit < overheadLimit) {
     overheadLimit = AddrAlignUp(overheadLimit, ChunkPageSize(chunk));
-    res = vmArenaMap(VMChunkVMArena(vmChunk), vmChunk->vm,
+    res = vmArenaMap(VMChunkVMArena(vmChunk), VMChunkVM(vmChunk),
                      vmChunk->overheadMappedLimit, overheadLimit);
     if (res != ResOK)
       goto failTableMap;
@@ -386,7 +392,7 @@ static Res VMChunkInit(Chunk chunk, BootBlock boot)
                   chunk->pageTable,
                   sizeof(PageUnion),
                   chunk->pages,
-                  saMapped, saPages, vmChunk->vm);
+                  saMapped, saPages, VMChunkVM(vmChunk));
 
   return ResOK;
 
@@ -403,7 +409,6 @@ failSaMapped:
 
 static Bool vmChunkDestroy(Tree tree, void *closureP, Size closureS)
 {
-  VM vm;
   Chunk chunk;
   VMChunk vmChunk;
 
@@ -423,9 +428,7 @@ static Bool vmChunkDestroy(Tree tree, void *closureP, Size closureS)
   SparseArrayFinish(&vmChunk->pages);
   
   vmChunk->sig = SigInvalid;
-  vm = vmChunk->vm;
   ChunkFinish(chunk);
-  VMDestroy(vm);
 
   return TRUE;
 }
@@ -435,11 +438,20 @@ static Bool vmChunkDestroy(Tree tree, void *closureP, Size closureS)
 
 static void VMChunkFinish(Chunk chunk)
 {
+  VMStruct vmStruct;
+  VM vm = &vmStruct;
   VMChunk vmChunk = Chunk2VMChunk(chunk);
 
-  vmArenaUnmap(VMChunkVMArena(vmChunk), vmChunk->vm,
-               VMBase(vmChunk->vm), vmChunk->overheadMappedLimit);
+  /* Copy VM descriptor to stack-local storage so that we can continue
+   * using the descriptor after the VM has been unmapped. */
+  (void)mps_lib_memcpy(vm, VMChunkVM(vmChunk), sizeof *vm);
+
+  vmArenaUnmap(VMChunkVMArena(vmChunk), vm,
+               VMBase(vm), vmChunk->overheadMappedLimit);
+
   /* No point in finishing the other fields, since they are unmapped. */
+
+  VMDestroy(vm);
 }
 
 
@@ -499,7 +511,8 @@ static Res VMArenaInit(Arena *arenaReturn, ArenaClass class, ArgList args)
   Res res;
   VMArena vmArena;
   Arena arena;
-  VM arenaVM;
+  VMStruct vmStruct;
+  VM vm = &vmStruct;
   Chunk chunk;
   mps_arg_s arg;
   char vmParams[VMParamSize];
@@ -524,24 +537,26 @@ static Res VMArenaInit(Arena *arenaReturn, ArenaClass class, ArgList args)
   if (res != ResOK)
     goto failVMCreate;
 
-  /* Create a VM to hold the arena and map it. */
+  /* Create a VM to hold the arena and map it. Store descriptor on the
+     stack until we have the arena to put it in. */
   vmArenaSize = SizeAlignUp(sizeof(VMArenaStruct), MPS_PF_ALIGN);
-  res = VMCreate(&arenaVM, vmArenaSize, grainSize, vmParams);
+  res = VMCreate(vm, vmArenaSize, grainSize, vmParams);
   if (res != ResOK)
     goto failVMCreate;
-  res = VMMap(arenaVM, VMBase(arenaVM), VMLimit(arenaVM));
+  res = VMMap(vm, VMBase(vm), VMLimit(vm));
   if (res != ResOK)
     goto failVMMap;
-  vmArena = (VMArena)VMBase(arenaVM);
+  vmArena = (VMArena)VMBase(vm);
 
   arena = VMArena2Arena(vmArena);
   /* <code/arena.c#init.caller> */
   res = ArenaInit(arena, class, grainSize, args);
   if (res != ResOK)
     goto failArenaInit;
-  arena->committed = VMMapped(arenaVM);
+  arena->committed = VMMapped(vm);
 
-  vmArena->vm = arenaVM;
+  /* Copy VM descriptor into its place in the arena. */
+  (void)mps_lib_memcpy(VMArenaVM(vmArena), vm, sizeof *vm);
   vmArena->spareSize = 0;
   RingInit(&vmArena->spareRing);
 
@@ -587,9 +602,9 @@ static Res VMArenaInit(Arena *arenaReturn, ArenaClass class, ArgList args)
 failChunkCreate:
   ArenaFinish(arena);
 failArenaInit:
-  VMUnmap(arenaVM, VMBase(arenaVM), VMLimit(arenaVM));
+  VMUnmap(vm, VMBase(vm), VMLimit(vm));
 failVMMap:
-  VMDestroy(arenaVM);
+  VMDestroy(vm);
 failVMCreate:
   return res;
 }
@@ -599,12 +614,12 @@ failVMCreate:
 
 static void VMArenaFinish(Arena arena)
 {
+  VMStruct vmStruct;
+  VM vm = &vmStruct;
   VMArena vmArena;
-  VM arenaVM;
 
   vmArena = Arena2VMArena(arena);
   AVERT(VMArena, vmArena);
-  arenaVM = vmArena->vm;
 
   EVENT1(ArenaDestroy, vmArena);
 
@@ -618,14 +633,17 @@ static void VMArenaFinish(Arena arena)
   RingFinish(&vmArena->spareRing);
 
   /* Destroying the chunks should leave only the arena's own VM. */
-  AVER(arena->committed == VMMapped(arenaVM));
+  AVER(arena->committed == VMMapped(VMArenaVM(vmArena)));
 
   vmArena->sig = SigInvalid;
 
   ArenaFinish(arena); /* <code/global.c#finish.caller> */
 
-  VMUnmap(arenaVM, VMBase(arenaVM), VMLimit(arenaVM));
-  VMDestroy(arenaVM);
+  /* Copy VM descriptor to stack-local storage so that we can continue
+   * using the descriptor after the VM has been unmapped. */
+  (void)mps_lib_memcpy(vm, VMArenaVM(vmArena), sizeof *vm);
+  VMUnmap(vm, VMBase(vm), VMLimit(vm));
+  VMDestroy(vm);
 }
 
 
@@ -642,7 +660,7 @@ static Size VMArenaReserved(Arena arena)
   reserved = 0;
   RING_FOR(node, &arena->chunkRing, next) {
     VMChunk vmChunk = Chunk2VMChunk(RING_ELT(Chunk, chunkRing, node));
-    reserved += VMReserved(vmChunk->vm);
+    reserved += VMReserved(VMChunkVM(vmChunk));
   }
   return reserved;
 }
@@ -779,19 +797,19 @@ static void sparePageRelease(VMChunk vmChunk, Index pi)
 
 static Res pageDescMap(VMChunk vmChunk, Index basePI, Index limitPI)
 {
-  Size before = VMMapped(vmChunk->vm);
+  Size before = VMMapped(VMChunkVM(vmChunk));
   Arena arena = VMArena2Arena(VMChunkVMArena(vmChunk));
   Res res = SparseArrayMap(&vmChunk->pages, basePI, limitPI);
-  arena->committed += VMMapped(vmChunk->vm) - before;
+  arena->committed += VMMapped(VMChunkVM(vmChunk)) - before;
   return res;
 }
 
 static void pageDescUnmap(VMChunk vmChunk, Index basePI, Index limitPI)
 {
-  Size before = VMMapped(vmChunk->vm);
+  Size before = VMMapped(VMChunkVM(vmChunk));
   Arena arena = VMArena2Arena(VMChunkVMArena(vmChunk));
   SparseArrayUnmap(&vmChunk->pages, basePI, limitPI);
-  arena->committed += VMMapped(vmChunk->vm) - before;
+  arena->committed += VMMapped(VMChunkVM(vmChunk)) - before;
 }
 
 
@@ -821,7 +839,7 @@ static Res pagesMarkAllocated(VMArena vmArena, VMChunk vmChunk,
     res = pageDescMap(vmChunk, j, k);
     if (res != ResOK)
       goto failSAMap;
-    res = vmArenaMap(vmArena, vmChunk->vm,
+    res = vmArenaMap(vmArena, VMChunkVM(vmChunk),
                      PageIndexBase(chunk, j), PageIndexBase(chunk, k));
     if (res != ResOK)
       goto failVMMap;
@@ -845,7 +863,7 @@ failSAMap:
   /* region from basePI to j needs deallocating */
   /* TODO: Consider making pages spare instead, then purging. */
   if (basePI < j) {
-    vmArenaUnmap(vmArena, vmChunk->vm,
+    vmArenaUnmap(vmArena, VMChunkVM(vmChunk),
                  PageIndexBase(chunk, basePI),
                  PageIndexBase(chunk, j));
     for (i = basePI; i < j; ++i)
@@ -938,7 +956,7 @@ static Size chunkUnmapAroundPage(Chunk chunk, Size size, Page page)
   }
 
   vmArenaUnmap(VMChunkVMArena(vmChunk),
-               vmChunk->vm,
+               VMChunkVM(vmChunk),
                PageIndexBase(chunk, basePI),
                PageIndexBase(chunk, limitPI));
 
diff --git a/mps/code/mpm.c b/mps/code/mpm.c
index 23ad83ad1c5..dcef8cae069 100644
--- a/mps/code/mpm.c
+++ b/mps/code/mpm.c
@@ -10,6 +10,8 @@
 
 #include "check.h"
 #include "mpm.h"
+#include "vm.h"
+
 #include <stdarg.h>
 /* Get some floating constants for WriteDouble */
 #include <float.h>
diff --git a/mps/code/mpm.h b/mps/code/mpm.h
index 0a6f3a8eff9..c76beb65c1b 100644
--- a/mps/code/mpm.h
+++ b/mps/code/mpm.h
@@ -1000,21 +1000,6 @@ typedef Res (*RootIterateFn)(Root root, void *p);
 extern Res RootsIterate(Globals arena, RootIterateFn f, void *p);
 
 
-/* VM Interface -- see <code/vm*.c> */
-
-extern Size VMPageSize(void);
-extern Bool VMCheck(VM vm);
-extern Res VMParamFromArgs(void *params, size_t paramSize, ArgList args);
-extern Res VMCreate(VM *VMReturn, Size size, Size grainSize, void *params);
-extern void VMDestroy(VM vm);
-extern Addr VMBase(VM vm);
-extern Addr VMLimit(VM vm);
-extern Res VMMap(VM vm, Addr base, Addr limit);
-extern void VMUnmap(VM vm, Addr base, Addr limit);
-extern Size VMReserved(VM vm);
-extern Size VMMapped(VM vm);
-
-
 /* Land Interface -- see <design/land/> */
 
 extern Bool LandCheck(Land land);
diff --git a/mps/code/protw3.c b/mps/code/protw3.c
index 3772a109c18..d74070cf46a 100644
--- a/mps/code/protw3.c
+++ b/mps/code/protw3.c
@@ -8,6 +8,7 @@
 /* prmcw3.h needed to share MutatorFaultContextStruct declation */
 /* with <code/prmcw3i3.c> */
 #include "prmcw3.h"
+#include "vm.h"
 
 #ifndef MPS_OS_W3
 #error "protw3.c is Win32-specific, but MPS_OS_W3 is not set"
diff --git a/mps/code/protxc.c b/mps/code/protxc.c
index 41d9e234ba4..1108e4ec67d 100644
--- a/mps/code/protxc.c
+++ b/mps/code/protxc.c
@@ -58,6 +58,7 @@
 #include "mpm.h"
 #include "prmcxc.h"
 #include "protxc.h"
+#include "vm.h"
 
 #include <stdlib.h> /* see .trans.stdlib */
 #include <stdio.h> /* see .trans.stdlib */
diff --git a/mps/code/sa.c b/mps/code/sa.c
index 5df8ed2f4b5..8e197494f55 100644
--- a/mps/code/sa.c
+++ b/mps/code/sa.c
@@ -7,6 +7,7 @@
 #include "sa.h"
 #include "mpm.h"
 #include "bt.h"
+#include "vm.h"
 
 static Index pagesLength(SparseArray sa)
 {
diff --git a/mps/code/vm.h b/mps/code/vm.h
new file mode 100644
index 00000000000..6fa0b492333
--- /dev/null
+++ b/mps/code/vm.h
@@ -0,0 +1,81 @@
+/* vm.h: VIRTUAL MEMOEY INTERFACE
+ *
+ * $Id: //info.ravenbrook.com/project/mps/branch/2014-06-14/vm/code/sa.h#2 $
+ * Copyright (c) 2014 Ravenbrook Limited.  See end of file for license.
+ */
+
+#ifndef vm_h
+#define vm_h
+
+#include "mpmtypes.h"
+
+
+/* VMStruct -- virtual memory structure */
+
+#define VMSig           ((Sig)0x519B3999) /* SIGnature VM */
+
+typedef struct VMStruct {
+  Sig sig;                      /* <design/sig/> */
+  void *block;                  /* unaligned base of mmap'd memory */
+  Addr base, limit;             /* aligned boundaries of reserved space */
+  Size reserved;                /* total reserved address space */
+  Size mapped;                  /* total mapped memory */
+} VMStruct;
+
+
+extern Size VMPageSize(void);
+extern Bool VMCheck(VM vm);
+extern Res VMParamFromArgs(void *params, size_t paramSize, ArgList args);
+extern Res VMCreate(VM vmReturn, Size size, Size grainSize, void *params);
+extern void VMDestroy(VM vm);
+extern Addr VMBase(VM vm);
+extern Addr VMLimit(VM vm);
+extern Res VMMap(VM vm, Addr base, Addr limit);
+extern void VMUnmap(VM vm, Addr base, Addr limit);
+extern Size VMReserved(VM vm);
+extern Size VMMapped(VM vm);
+
+
+#endif /* vm_h */
+
+
+/* C. COPYRIGHT AND LICENSE
+ *
+ * Copyright (C) 2014 Ravenbrook Limited <http://www.ravenbrook.com/>.
+ * All rights reserved.  This is an open source license.  Contact
+ * Ravenbrook for commercial licensing options.
+ * 
+ * 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. Redistributions in any form must be accompanied by information on how
+ * to obtain complete source code for this software and any accompanying
+ * software that uses this software.  The source code must either be
+ * included in the distribution or be available for no more than the cost
+ * of distribution plus a nominal fee, and must be freely redistributable
+ * under reasonable conditions.  For an executable file, complete source
+ * code means the source code for all modules it contains. It does not
+ * include source code for modules or files that typically accompany the
+ * major components of the operating system on which the executable file
+ * runs.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
+ * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
+ * PURPOSE, OR NON-INFRINGEMENT, ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT HOLDERS AND 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.
+ */
diff --git a/mps/code/vman.c b/mps/code/vman.c
index 0420c6a95a6..ea4850b0c28 100644
--- a/mps/code/vman.c
+++ b/mps/code/vman.c
@@ -5,6 +5,7 @@
  */
 
 #include "mpm.h"
+#include "vm.h"
 
 #include <stdlib.h>     /* for malloc and free */
 #include <string.h>     /* for memset */
@@ -12,20 +13,6 @@
 SRCID(vman, "$Id$");
 
 
-/* VMStruct -- virtual memory structure */
-
-#define VMSig           ((Sig)0x519B3999) /* SIGnature VM */
-
-/* ANSI fake VM structure, see <design/vman/> */
-typedef struct VMStruct {
-  Sig sig;                      /* <design/sig/> */
-  void *block;                  /* pointer to malloc'd block, for free() */
-  Addr base, limit;             /* aligned boundaries of malloc'd memory */
-  Size reserved;                /* total reserved address space */
-  Size mapped;                  /* total mapped memory */
-} VMStruct;
-
-
 /* VMCheck -- check a VM structure */
 
 Bool VMCheck(VM vm)
@@ -63,12 +50,11 @@ Res VMParamFromArgs(void *params, size_t paramSize, ArgList args)
 
 /* VMCreate -- reserve some virtual address space, and create a VM structure */
 
-Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
+Res VMCreate(VM vm, Size size, Size grainSize, void *params)
 {
-  VM vm;
   Size pageSize;
 
-  AVER(vmReturn != NULL);
+  AVER(vm != NULL);
   AVERT(ArenaGrainSize, grainSize);
   AVER(size > 0);
   AVER(params != NULL);
@@ -90,14 +76,8 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   if (reserved < grainSize || reserved > (Size)(size_t)-1)
     return ResRESOURCE;
 
-  /* Allocate space to store the descriptor. */
-  vm = (VM)malloc(sizeof(VMStruct));
-  if (vm == NULL)
-    return ResMEMORY;
-
   vm->block = malloc((size_t)reserved);
   if (vm->block == NULL) {
-    free(vm);
     return ResMEMORY;
   }
 
@@ -112,11 +92,9 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   vm->mapped = (Size)0;
  
   vm->sig = VMSig;
-
   AVERT(VM, vm);
  
   EVENT3(VMCreate, vm, vm->base, vm->limit);
-  *vmReturn = vm;
   return ResOK;
 }
 
diff --git a/mps/code/vmix.c b/mps/code/vmix.c
index c4ca0954325..35d2e6cb3d2 100644
--- a/mps/code/vmix.c
+++ b/mps/code/vmix.c
@@ -39,6 +39,7 @@
  */
 
 #include "mpm.h"
+#include "vm.h"
 
 /* for mmap(2), munmap(2) */
 #include <sys/types.h>
@@ -58,19 +59,6 @@
 SRCID(vmix, "$Id$");
 
 
-/* VMStruct -- virtual memory structure */
-
-#define VMSig           ((Sig)0x519B3999) /* SIGnature VM */
-
-typedef struct VMStruct {
-  Sig sig;                      /* <design/sig/> */
-  void *block;                  /* unaligned base of mmap'd memory */
-  Addr base, limit;             /* aligned boundaries of reserved space */
-  Size reserved;                /* total reserved address space */
-  Size mapped;                  /* total mapped memory */
-} VMStruct;
-
-
 /* VMPageSize -- return operating system page size */
 
 Size VMPageSize(void)
@@ -114,14 +102,12 @@ Res VMParamFromArgs(void *params, size_t paramSize, ArgList args)
 
 /* VMCreate -- reserve some virtual address space, and create a VM structure */
 
-Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
+Res VMCreate(VM vm, Size size, Size grainSize, void *params)
 {
-  VM vm;
   Size pageSize, reserved;
   void *addr;
-  Res res;
 
-  AVER(vmReturn != NULL);
+  AVER(vm != NULL);
   AVERT(ArenaGrainSize, grainSize);
   AVER(size > 0);
   AVER(params != NULL);
@@ -139,10 +125,9 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   if (reserved < grainSize || reserved > (Size)(size_t)-1)
     return ResRESOURCE;
 
-  /* Map in a page to store the descriptor on. */
-  addr = mmap(0, (size_t)SizeAlignUp(sizeof(VMStruct), pageSize),
-              PROT_READ | PROT_WRITE,
-              MAP_ANON | MAP_PRIVATE,
+  /* See .assume.not-last. */
+  addr = mmap(0, reserved,
+              PROT_NONE, MAP_ANON | MAP_PRIVATE,
               -1, 0);
   /* On Darwin the MAP_FAILED return value is not documented, but does
    * work.  MAP_FAILED _is_ documented by POSIX.
@@ -150,19 +135,7 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   if(addr == MAP_FAILED) {
     int e = errno;
     AVER(e == ENOMEM); /* .assume.mmap.err */
-    return ResMEMORY;
-  }
-  vm = (VM)addr;
-
-  /* See .assume.not-last. */
-  addr = mmap(0, reserved,
-              PROT_NONE, MAP_ANON | MAP_PRIVATE,
-              -1, 0);
-  if(addr == MAP_FAILED) {
-    int e = errno;
-    AVER(e == ENOMEM); /* .assume.mmap.err */
-    res = ResRESOURCE;
-    goto failReserve;
+    return ResRESOURCE;
   }
 
   vm->block = addr;
@@ -177,13 +150,7 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   AVERT(VM, vm);
 
   EVENT3(VMCreate, vm, vm->base, vm->limit);
-
-  *vmReturn = vm;
   return ResOK;
-
-failReserve:
-  (void)munmap((void *)vm, (size_t)SizeAlignUp(sizeof(VMStruct), pageSize));
-  return res;
 }
 
 
@@ -198,16 +165,14 @@ void VMDestroy(VM vm)
 
   EVENT1(VMDestroy, vm);
 
-  /* This appears to be pretty pointless, since the descriptor */
-  /* page is about to vanish completely.  However, munmap might fail */
-  /* for some reason, and this would ensure that it was still */
-  /* discovered if sigs were being checked. */
+  /* This appears to be pretty pointless, since the VM is about to
+   * vanish completely. However, munmap might fail for some reason,
+   * and this would ensure that it was still discovered if sigs are
+   * being checked. */
   vm->sig = SigInvalid;
 
   r = munmap(vm->block, vm->reserved);
   AVER(r == 0);
-  r = munmap((void *)vm, (size_t)SizeAlignUp(sizeof(VMStruct), VMPageSize()));
-  AVER(r == 0);
 }
 
 
diff --git a/mps/code/vmw3.c b/mps/code/vmw3.c
index 845eb871473..ee93e5e9215 100644
--- a/mps/code/vmw3.c
+++ b/mps/code/vmw3.c
@@ -39,32 +39,17 @@
  */
 
 #include "mpm.h"
+#include "vm.h"
 
 #ifndef MPS_OS_W3
 #error "vmw3.c is Win32 specific, but MPS_OS_W3 is not set"
 #endif
-#ifdef VM_RM
-#error "vmw3.c compiled with VM_RM set"
-#endif
 
 #include "mpswin.h"
 
 SRCID(vmw3, "$Id$");
 
 
-/* VMStruct -- virtual memory structure */
-
-#define VMSig           ((Sig)0x519B3999) /* SIGnature VM */
-
-typedef struct VMStruct {
-  Sig sig;                      /* <design/sig/> */
-  void *block;                  /* unaligned base of VirtualAlloc'd space */
-  Addr base, limit;             /* aligned boundaries of reserved space */
-  Size reserved;                /* total reserved address space */
-  Size mapped;                  /* total mapped memory */
-} VMStruct;
-
-
 /* VMPageSize -- return the operating system page size */
 
 Size VMPageSize(void)
@@ -123,16 +108,14 @@ Res VMParamFromArgs(void *params, size_t paramSize, ArgList args)
 
 /* VMCreate -- reserve some virtual address space, and create a VM structure */
 
-Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
+Res VMCreate(VM vm, Size size, Size grainSize, void *params)
 {
   LPVOID vbase;
-  VM vm;
   Size pageSize, reserved;
   Res res;
-  BOOL b;
   VMParams vmParams = params;
 
-  AVER(vmReturn != NULL);
+  AVER(vm != NULL);
   AVERT(ArenaGrainSize, grainSize);
   AVER(size > 0);
   AVER(params != NULL); /* FIXME: Should have full AVERT? */
@@ -153,13 +136,6 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   if (reserved < grainSize || reserved > (Size)(SIZE_T)-1)
     return ResRESOURCE;
 
-  /* Allocate the vm descriptor.  This is likely to be wasteful. */
-  vbase = VirtualAlloc(NULL, SizeAlignUp(sizeof(VMStruct), pageSize),
-                       MEM_COMMIT, PAGE_READWRITE);
-  if (vbase == NULL)
-    return ResMEMORY;
-  vm = (VM)vbase;
-
   /* Allocate the address space. */
   vbase = VirtualAlloc(NULL,
                        reserved,
@@ -167,10 +143,8 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
                          MEM_RESERVE | MEM_TOP_DOWN :
                          MEM_RESERVE,
                        PAGE_NOACCESS);
-  if (vbase == NULL) {
-    res = ResRESOURCE;
-    goto failReserve;
-  }
+  if (vbase == NULL)
+    return ResRESOURCE;
 
   AVER(AddrIsAligned(vbase, pageSize));
 
@@ -186,14 +160,7 @@ Res VMCreate(VM *vmReturn, Size size, Size grainSize, void *params)
   AVERT(VM, vm);
 
   EVENT3(VMCreate, vm, vm->base, vm->limit);
-
-  *vmReturn = vm;
   return ResOK;
-
-failReserve:
-  b = VirtualFree((LPVOID)vm, (SIZE_T)0, MEM_RELEASE);
-  AVER(b != 0);
-  return res;
 }