MMPagePool.cpp@ 30045

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1	/* $Id: MMPagePool.cpp 28800 2010-04-27 08:22:32Z vboxsync $ */
2	/** @file
3	* MM - Memory Manager - Page Pool.
4	*/
5
6	/*
7	* Copyright (C) 2006-2007 Oracle Corporation
8	*
9	* This file is part of VirtualBox Open Source Edition (OSE), as
10	* available from http://www.virtualbox.org. This file is free software;
11	* you can redistribute it and/or modify it under the terms of the GNU
12	* General Public License (GPL) as published by the Free Software
13	* Foundation, in version 2 as it comes in the "COPYING" file of the
14	* VirtualBox OSE distribution. VirtualBox OSE is distributed in the
15	* hope that it will be useful, but WITHOUT ANY WARRANTY of any kind.
16	*/
17
18	/*******************************************************************************
19	* Header Files *
20	*******************************************************************************/
21	#define LOG_GROUP LOG_GROUP_MM_POOL
22	#include <VBox/mm.h>
23	#include <VBox/pgm.h>
24	#include <VBox/stam.h>
25	#include "MMInternal.h"
26	#include <VBox/vm.h>
27	#include <VBox/param.h>
28	#include <VBox/err.h>
29	#include <VBox/log.h>
30	#include <iprt/alloc.h>
31	#include <iprt/assert.h>
32	#define USE_INLINE_ASM_BIT_OPS
33	#ifdef USE_INLINE_ASM_BIT_OPS
34	# include <iprt/asm.h>
35	#endif
36	#include <iprt/string.h>
37
38
39
40	/*******************************************************************************
41	* Internal Functions *
42	*******************************************************************************/
43	#ifdef IN_RING3
44	static void * mmR3PagePoolAlloc(PMMPAGEPOOL pPool);
45	static void mmR3PagePoolFree(PMMPAGEPOOL pPool, void *pv);
46	#endif
47
48
49	/**
50	* Initializes the page pool
51	*
52	* @return VBox status.
53	* @param pVM VM handle.
54	* @thread The Emulation Thread.
55	*/
56	int mmR3PagePoolInit(PVM pVM)
57	{
58	AssertMsg(!pVM->mm.s.pPagePoolR3, ("Already initialized!\n"));
59
60	/*
61	* Allocate the pool structures.
62	*/
63	/** @todo @bufref{1865},@bufref{3202}: mapping the page pool page into
64	* ring-0. Need to change the wasy we allocate it... */
65	AssertReleaseReturn(sizeof(pVM->mm.s.pPagePoolR3) + sizeof(pVM->mm.s.pPagePoolLowR3) < PAGE_SIZE, VERR_INTERNAL_ERROR);
66	int rc = SUPR3PageAllocEx(1, 0 /fFlags/, (void *)&pVM->mm.s.pPagePoolR3, NULL /pR0Ptr/, NULL /paPages*/);
67	if (RT_FAILURE(rc))
68	return rc;
69	memset(pVM->mm.s.pPagePoolR3, 0, PAGE_SIZE);
70	pVM->mm.s.pPagePoolR3->pVM = pVM;
71	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cPages, STAMTYPE_U32, "/MM/Page/Def/cPages", STAMUNIT_PAGES, "Number of pages in the default pool.");
72	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cFreePages, STAMTYPE_U32, "/MM/Page/Def/cFreePages", STAMUNIT_PAGES, "Number of free pages in the default pool.");
73	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cSubPools, STAMTYPE_U32, "/MM/Page/Def/cSubPools", STAMUNIT_COUNT, "Number of sub pools in the default pool.");
74	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cAllocCalls, STAMTYPE_COUNTER, "/MM/Page/Def/cAllocCalls", STAMUNIT_CALLS, "Number of MMR3PageAlloc() calls for the default pool.");
75	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cFreeCalls, STAMTYPE_COUNTER, "/MM/Page/Def/cFreeCalls", STAMUNIT_CALLS, "Number of MMR3PageFree()+MMR3PageFreeByPhys() calls for the default pool.");
76	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cToPhysCalls, STAMTYPE_COUNTER, "/MM/Page/Def/cToPhysCalls", STAMUNIT_CALLS, "Number of MMR3Page2Phys() calls for this pool.");
77	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cToVirtCalls, STAMTYPE_COUNTER, "/MM/Page/Def/cToVirtCalls", STAMUNIT_CALLS, "Number of MMR3PagePhys2Page()+MMR3PageFreeByPhys() calls for the default pool.");
78	STAM_REG(pVM, &pVM->mm.s.pPagePoolR3->cErrors, STAMTYPE_COUNTER, "/MM/Page/Def/cErrors", STAMUNIT_ERRORS,"Number of errors for the default pool.");
79
80	pVM->mm.s.pPagePoolLowR3 = pVM->mm.s.pPagePoolR3 + 1;
81	pVM->mm.s.pPagePoolLowR3->pVM = pVM;
82	pVM->mm.s.pPagePoolLowR3->fLow = true;
83	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cPages, STAMTYPE_U32, "/MM/Page/Low/cPages", STAMUNIT_PAGES, "Number of pages in the <4GB pool.");
84	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cFreePages, STAMTYPE_U32, "/MM/Page/Low/cFreePages", STAMUNIT_PAGES, "Number of free pages in the <4GB pool.");
85	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cSubPools, STAMTYPE_U32, "/MM/Page/Low/cSubPools", STAMUNIT_COUNT, "Number of sub pools in the <4GB pool.");
86	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cAllocCalls, STAMTYPE_COUNTER, "/MM/Page/Low/cAllocCalls", STAMUNIT_CALLS, "Number of MMR3PageAllocLow() calls for the <4GB pool.");
87	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cFreeCalls, STAMTYPE_COUNTER, "/MM/Page/Low/cFreeCalls", STAMUNIT_CALLS, "Number of MMR3PageFreeLow()+MMR3PageFreeByPhys() calls for the <4GB pool.");
88	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cToPhysCalls,STAMTYPE_COUNTER, "/MM/Page/Low/cToPhysCalls", STAMUNIT_CALLS, "Number of MMR3Page2Phys() calls for the <4GB pool.");
89	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cToVirtCalls,STAMTYPE_COUNTER, "/MM/Page/Low/cToVirtCalls", STAMUNIT_CALLS, "Number of MMR3PagePhys2Page()+MMR3PageFreeByPhys() calls for the <4GB pool.");
90	STAM_REG(pVM, &pVM->mm.s.pPagePoolLowR3->cErrors, STAMTYPE_COUNTER, "/MM/Page/Low/cErrors", STAMUNIT_ERRORS,"Number of errors for the <4GB pool.");
91
92	#ifndef VBOX_WITH_2X_4GB_ADDR_SPACE
93	pVM->mm.s.pPagePoolR0 = (uintptr_t)pVM->mm.s.pPagePoolR3;
94	pVM->mm.s.pPagePoolLowR0 = (uintptr_t)pVM->mm.s.pPagePoolLowR3;
95	#endif
96
97	/** @todo init a mutex? */
98	return VINF_SUCCESS;
99	}
100
101
102	/**
103	* Release all locks and free the allocated memory.
104	*
105	* @param pVM VM handle.
106	* @thread The Emulation Thread.
107	*/
108	void mmR3PagePoolTerm(PVM pVM)
109	{
110	if (pVM->mm.s.pPagePoolR3)
111	{
112	/*
113	* Unlock all memory held by subpools and free the memory.
114	* (The MM Heap will free the memory used for internal stuff.)
115	*/
116	Assert(!pVM->mm.s.pPagePoolR3->fLow);
117	PMMPAGESUBPOOL pSubPool = pVM->mm.s.pPagePoolR3->pHead;
118	while (pSubPool)
119	{
120	int rc = SUPR3PageFreeEx(pSubPool->pvPages, pSubPool->cPages);
121	AssertMsgRC(rc, ("SUPR3PageFreeEx(%p) failed with rc=%Rrc\n", pSubPool->pvPages, rc));
122	pSubPool->pvPages = NULL;
123
124	/* next */
125	pSubPool = pSubPool->pNext;
126	}
127	pVM->mm.s.pPagePoolR3 = NULL;
128	#ifndef VBOX_WITH_2X_4GB_ADDR_SPACE
129	pVM->mm.s.pPagePoolR0 = NIL_RTR0PTR;
130	#endif
131	}
132
133	if (pVM->mm.s.pPagePoolLowR3)
134	{
135	/*
136	* Free the memory.
137	*/
138	Assert(pVM->mm.s.pPagePoolLowR3->fLow);
139	PMMPAGESUBPOOL pSubPool = pVM->mm.s.pPagePoolLowR3->pHead;
140	while (pSubPool)
141	{
142	int rc = SUPR3LowFree(pSubPool->pvPages, pSubPool->cPages);
143	AssertMsgRC(rc, ("SUPR3LowFree(%p) failed with rc=%d\n", pSubPool->pvPages, rc));
144	pSubPool->pvPages = NULL;
145
146	/* next */
147	pSubPool = pSubPool->pNext;
148	}
149	pVM->mm.s.pPagePoolLowR3 = NULL;
150	#ifndef VBOX_WITH_2X_4GB_ADDR_SPACE
151	pVM->mm.s.pPagePoolLowR0 = NIL_RTR0PTR;
152	#endif
153	}
154	}
155
156
157	/**
158	* Allocates a page from the page pool.
159	*
160	* @returns Pointer to allocated page(s).
161	* @returns NULL on failure.
162	* @param pPool Pointer to the page pool.
163	* @thread The Emulation Thread.
164	*/
165	DECLINLINE(void *) mmR3PagePoolAlloc(PMMPAGEPOOL pPool)
166	{
167	VM_ASSERT_EMT(pPool->pVM);
168	STAM_COUNTER_INC(&pPool->cAllocCalls);
169
170	/*
171	* Walk free list.
172	*/
173	if (pPool->pHeadFree)
174	{
175	PMMPAGESUBPOOL pSub = pPool->pHeadFree;
176	/* decrement free count and unlink if no more free entries. */
177	if (!--pSub->cPagesFree)
178	pPool->pHeadFree = pSub->pNextFree;
179	#ifdef VBOX_WITH_STATISTICS
180	pPool->cFreePages--;
181	#endif
182
183	/* find free spot in bitmap. */
184	#ifdef USE_INLINE_ASM_BIT_OPS
185	const int iPage = ASMBitFirstClear(pSub->auBitmap, pSub->cPages);
186	if (iPage >= 0)
187	{
188	Assert(!ASMBitTest(pSub->auBitmap, iPage));
189	ASMBitSet(pSub->auBitmap, iPage);
190	return (uint8_t )pSub->pvPages + PAGE_SIZE iPage;
191	}
192	#else
193	unsigned *pu = &pSub->auBitmap[0];
194	unsigned puEnd = &pSub->auBitmap[pSub->cPages / (sizeof(pSub->auBitmap) 8)];
195	while (pu < puEnd)
196	{
197	unsigned u;
198	if ((u = *pu) != ~0U)
199	{
200	unsigned iBit = 0;
201	unsigned uMask = 1;
202	while (iBit < sizeof(pSub->auBitmap[0]) * 8)
203	{
204	if (!(u & uMask))
205	{
206	*pu \|= uMask;
207	return (uint8_t *)pSub->pvPages
208	+ PAGE_SIZE * (iBit + ((uint8_t )pu - (uint8_t )&pSub->auBitmap[0]) * 8);
209	}
210	iBit++;
211	uMask <<= 1;
212	}
213	STAM_COUNTER_INC(&pPool->cErrors);
214	AssertMsgFailed(("how odd, expected to find a free bit in %#x, but didn't\n", u));
215	}
216	/* next */
217	pu++;
218	}
219	#endif
220	STAM_COUNTER_INC(&pPool->cErrors);
221	#ifdef VBOX_WITH_STATISTICS
222	pPool->cFreePages++;
223	#endif
224	AssertMsgFailed(("how strange, expected to find a free bit in %p, but didn't (%d pages supposed to be free!)\n", pSub, pSub->cPagesFree + 1));
225	}
226
227	/*
228	* Allocate new subpool.
229	*/
230	unsigned cPages = !pPool->fLow ? 128 : 32;
231	PMMPAGESUBPOOL pSub;
232	int rc = MMHyperAlloc(pPool->pVM,
233	RT_OFFSETOF(MMPAGESUBPOOL, auBitmap[cPages / (sizeof(pSub->auBitmap[0] * 8))])
234	+ (sizeof(SUPPAGE) + sizeof(MMPPLOOKUPHCPHYS)) * cPages
235	+ sizeof(MMPPLOOKUPHCPTR),
236	0,
237	MM_TAG_MM_PAGE,
238	(void **)&pSub);
239	if (RT_FAILURE(rc))
240	return NULL;
241
242	PSUPPAGE paPhysPages = (PSUPPAGE)&pSub->auBitmap[cPages / (sizeof(pSub->auBitmap[0]) * 8)];
243	Assert((uintptr_t)paPhysPages >= (uintptr_t)&pSub->auBitmap[1]);
244	if (!pPool->fLow)
245	{
246	rc = SUPR3PageAllocEx(cPages,
247	0 /* fFlags */,
248	&pSub->pvPages,
249	NULL,
250	paPhysPages);
251	if (RT_FAILURE(rc))
252	rc = VMSetError(pPool->pVM, rc, RT_SRC_POS,
253	N_("Failed to lock host %zd bytes of memory (out of memory)"), (size_t)cPages << PAGE_SHIFT);
254	}
255	else
256	rc = SUPR3LowAlloc(cPages, &pSub->pvPages, NULL, paPhysPages);
257	if (RT_SUCCESS(rc))
258	{
259	/*
260	* Setup the sub structure and allocate the requested page.
261	*/
262	pSub->cPages = cPages;
263	pSub->cPagesFree= cPages - 1;
264	pSub->paPhysPages = paPhysPages;
265	memset(pSub->auBitmap, 0, cPages / 8);
266	/* allocate first page. */
267	pSub->auBitmap[0] \|= 1;
268	/* link into free chain. */
269	pSub->pNextFree = pPool->pHeadFree;
270	pPool->pHeadFree= pSub;
271	/* link into main chain. */
272	pSub->pNext = pPool->pHead;
273	pPool->pHead = pSub;
274	/* update pool statistics. */
275	pPool->cSubPools++;
276	pPool->cPages += cPages;
277	#ifdef VBOX_WITH_STATISTICS
278	pPool->cFreePages += cPages - 1;
279	#endif
280
281	/*
282	* Initialize the physical pages with backpointer to subpool.
283	*/
284	unsigned i = cPages;
285	while (i-- > 0)
286	{
287	AssertMsg(paPhysPages[i].Phys && !(paPhysPages[i].Phys & PAGE_OFFSET_MASK),
288	("i=%d Phys=%d\n", i, paPhysPages[i].Phys));
289	paPhysPages[i].uReserved = (RTHCUINTPTR)pSub;
290	}
291
292	/*
293	* Initialize the physical lookup record with backpointers to the physical pages.
294	*/
295	PMMPPLOOKUPHCPHYS paLookupPhys = (PMMPPLOOKUPHCPHYS)&paPhysPages[cPages];
296	i = cPages;
297	while (i-- > 0)
298	{
299	paLookupPhys[i].pPhysPage = &paPhysPages[i];
300	paLookupPhys[i].Core.Key = paPhysPages[i].Phys;
301	RTAvlHCPhysInsert(&pPool->pLookupPhys, &paLookupPhys[i].Core);
302	}
303
304	/*
305	* And the one record for virtual memory lookup.
306	*/
307	PMMPPLOOKUPHCPTR pLookupVirt = (PMMPPLOOKUPHCPTR)&paLookupPhys[cPages];
308	pLookupVirt->pSubPool = pSub;
309	pLookupVirt->Core.Key = pSub->pvPages;
310	RTAvlPVInsert(&pPool->pLookupVirt, &pLookupVirt->Core);
311
312	/* return allocated page (first). */
313	return pSub->pvPages;
314	}
315
316	MMHyperFree(pPool->pVM, pSub);
317	STAM_COUNTER_INC(&pPool->cErrors);
318	if (pPool->fLow)
319	VMSetError(pPool->pVM, rc, RT_SRC_POS,
320	N_("Failed to expand page pool for memory below 4GB. Current size: %d pages"),
321	pPool->cPages);
322	AssertMsgFailed(("Failed to expand pool%s. rc=%Rrc poolsize=%d\n",
323	pPool->fLow ? " (<4GB)" : "", rc, pPool->cPages));
324	return NULL;
325	}
326
327
328	/**
329	* Frees a page from the page pool.
330	*
331	* @param pPool Pointer to the page pool.
332	* @param pv Pointer to the page to free.
333	* I.e. pointer returned by mmR3PagePoolAlloc().
334	* @thread The Emulation Thread.
335	*/
336	DECLINLINE(void) mmR3PagePoolFree(PMMPAGEPOOL pPool, void *pv)
337	{
338	VM_ASSERT_EMT(pPool->pVM);
339	STAM_COUNTER_INC(&pPool->cFreeCalls);
340
341	/*
342	* Lookup the virtual address.
343	*/
344	PMMPPLOOKUPHCPTR pLookup = (PMMPPLOOKUPHCPTR)RTAvlPVGetBestFit(&pPool->pLookupVirt, pv, false);
345	if ( !pLookup
346	\|\| (uint8_t )pv >= (uint8_t )pLookup->pSubPool->pvPages + (pLookup->pSubPool->cPages << PAGE_SHIFT)
347	)
348	{
349	STAM_COUNTER_INC(&pPool->cErrors);
350	AssertMsgFailed(("invalid pointer %p\n", pv));
351	return;
352	}
353
354	/*
355	* Free the page.
356	*/
357	PMMPAGESUBPOOL pSubPool = pLookup->pSubPool;
358	/* clear bitmap bit */
359	const unsigned iPage = ((uint8_t )pv - (uint8_t )pSubPool->pvPages) >> PAGE_SHIFT;
360	#ifdef USE_INLINE_ASM_BIT_OPS
361	Assert(ASMBitTest(pSubPool->auBitmap, iPage));
362	ASMBitClear(pSubPool->auBitmap, iPage);
363	#else
364	unsigned iBit = iPage % (sizeof(pSubPool->auBitmap[0]) * 8);
365	unsigned iIndex = iPage / (sizeof(pSubPool->auBitmap[0]) * 8);
366	pSubPool->auBitmap[iIndex] &= ~(1 << iBit);
367	#endif
368	/* update stats. */
369	pSubPool->cPagesFree++;
370	#ifdef VBOX_WITH_STATISTICS
371	pPool->cFreePages++;
372	#endif
373	if (pSubPool->cPagesFree == 1)
374	{
375	pSubPool->pNextFree = pPool->pHeadFree;
376	pPool->pHeadFree = pSubPool;
377	}
378	}
379
380
381	/**
382	* Allocates a page from the page pool.
383	*
384	* This function may returns pages which has physical addresses any
385	* where. If you require a page to be within the first 4GB of physical
386	* memory, use MMR3PageAllocLow().
387	*
388	* @returns Pointer to the allocated page page.
389	* @returns NULL on failure.
390	* @param pVM VM handle.
391	* @thread The Emulation Thread.
392	*/
393	VMMR3DECL(void *) MMR3PageAlloc(PVM pVM)
394	{
395	/* Note: unprotected by locks; currently fine as it's used during init or under the PGM lock */
396	return mmR3PagePoolAlloc(pVM->mm.s.pPagePoolR3);
397	}
398
399
400	/**
401	* Allocates a page from the page pool and return its physical address.
402	*
403	* This function may returns pages which has physical addresses any
404	* where. If you require a page to be within the first 4GB of physical
405	* memory, use MMR3PageAllocLow().
406	*
407	* @returns Pointer to the allocated page page.
408	* @returns NIL_RTHCPHYS on failure.
409	* @param pVM VM handle.
410	* @thread The Emulation Thread.
411	*/
412	VMMR3DECL(RTHCPHYS) MMR3PageAllocPhys(PVM pVM)
413	{
414	/* Note: unprotected by locks; currently fine as it's used during init or under the PGM lock */
415	/** @todo optimize this, it's the most common case now. */
416	void *pv = mmR3PagePoolAlloc(pVM->mm.s.pPagePoolR3);
417	if (pv)
418	return mmPagePoolPtr2Phys(pVM->mm.s.pPagePoolR3, pv);
419	return NIL_RTHCPHYS;
420	}
421
422
423	/**
424	* Frees a page allocated from the page pool by MMR3PageAlloc() or
425	* MMR3PageAllocPhys().
426	*
427	* @param pVM VM handle.
428	* @param pvPage Pointer to the page.
429	* @thread The Emulation Thread.
430	*/
431	VMMR3DECL(void) MMR3PageFree(PVM pVM, void *pvPage)
432	{
433	mmR3PagePoolFree(pVM->mm.s.pPagePoolR3, pvPage);
434	}
435
436
437	/**
438	* Allocates a page from the low page pool.
439	*
440	* @returns Pointer to the allocated page.
441	* @returns NULL on failure.
442	* @param pVM VM handle.
443	* @thread The Emulation Thread.
444	*/
445	VMMR3DECL(void *) MMR3PageAllocLow(PVM pVM)
446	{
447	return mmR3PagePoolAlloc(pVM->mm.s.pPagePoolLowR3);
448	}
449
450
451	/**
452	* Frees a page allocated from the page pool by MMR3PageAllocLow().
453	*
454	* @param pVM VM handle.
455	* @param pvPage Pointer to the page.
456	* @thread The Emulation Thread.
457	*/
458	VMMR3DECL(void) MMR3PageFreeLow(PVM pVM, void *pvPage)
459	{
460	mmR3PagePoolFree(pVM->mm.s.pPagePoolLowR3, pvPage);
461	}
462
463
464	/**
465	* Free a page allocated from the page pool by physical address.
466	* This works for pages allocated by MMR3PageAlloc(), MMR3PageAllocPhys()
467	* and MMR3PageAllocLow().
468	*
469	* @param pVM VM handle.
470	* @param HCPhysPage The physical address of the page to be freed.
471	* @thread The Emulation Thread.
472	*/
473	VMMR3DECL(void) MMR3PageFreeByPhys(PVM pVM, RTHCPHYS HCPhysPage)
474	{
475	void *pvPage = mmPagePoolPhys2Ptr(pVM->mm.s.pPagePoolR3, HCPhysPage);
476	if (!pvPage)
477	pvPage = mmPagePoolPhys2Ptr(pVM->mm.s.pPagePoolLowR3, HCPhysPage);
478	if (pvPage)
479	mmR3PagePoolFree(pVM->mm.s.pPagePoolR3, pvPage);
480	else
481	AssertMsgFailed(("Invalid address HCPhysPT=%#x\n", HCPhysPage));
482	}
483
484
485	/**
486	* Gets the HC pointer to the dummy page.
487	*
488	* The dummy page is used as a place holder to prevent potential bugs
489	* from doing really bad things to the system.
490	*
491	* @returns Pointer to the dummy page.
492	* @param pVM VM handle.
493	* @thread The Emulation Thread.
494	*/
495	VMMR3DECL(void *) MMR3PageDummyHCPtr(PVM pVM)
496	{
497	VM_ASSERT_EMT(pVM);
498	if (!pVM->mm.s.pvDummyPage)
499	{
500	pVM->mm.s.pvDummyPage = mmR3PagePoolAlloc(pVM->mm.s.pPagePoolR3);
501	AssertRelease(pVM->mm.s.pvDummyPage);
502	pVM->mm.s.HCPhysDummyPage = mmPagePoolPtr2Phys(pVM->mm.s.pPagePoolR3, pVM->mm.s.pvDummyPage);
503	AssertRelease(!(pVM->mm.s.HCPhysDummyPage & ~X86_PTE_PAE_PG_MASK));
504	}
505	return pVM->mm.s.pvDummyPage;
506	}
507
508
509	/**
510	* Gets the HC Phys to the dummy page.
511	*
512	* The dummy page is used as a place holder to prevent potential bugs
513	* from doing really bad things to the system.
514	*
515	* @returns Pointer to the dummy page.
516	* @param pVM VM handle.
517	* @thread The Emulation Thread.
518	*/
519	VMMR3DECL(RTHCPHYS) MMR3PageDummyHCPhys(PVM pVM)
520	{
521	VM_ASSERT_EMT(pVM);
522	if (!pVM->mm.s.pvDummyPage)
523	MMR3PageDummyHCPtr(pVM);
524	return pVM->mm.s.HCPhysDummyPage;
525	}
526

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source: vbox/trunk/src/VBox/VMM/MMPagePool.cpp@ 30045

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