[PATCH] Fix 2-on-3 shadow mode.

[PATCH] Fix 2-on-3 shadow mode.

[Gianluca Guida]

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A wrong #ifdef in multi.c may cause memory corruption in some 32 bit HVM 
guests.

This patch fixes it, and should be applied hopefully to xen-3.3 and 
unstable.

Thanks,
Gianluca


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diff -r 587e81dd3540 xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c	Mon Mar 02 14:19:35 2009 +0000
+++ b/xen/arch/x86/mm/shadow/multi.c	Tue Mar 17 13:11:46 2009 +0000
@@ -2753,14 +2753,13 @@ int sh_safe_not_to_sync(struct vcpu *v, 
         return 0;
     smfn = _mfn(sp->up >> PAGE_SHIFT);
     ASSERT(mfn_valid(smfn));
-
-#if (GUEST_PAGING_LEVELS == 2)
+#endif
+
+#if (GUEST_PAGING_LEVELS == 2 && SHADOW_PAGING_LEVELS == 3)
     /* In 2-on-3 shadow mode the up pointer contains the link to the
      * shadow page, but the shadow_table contains only the first of the
      * four pages that makes the PAE top shadow tables. */
     smfn = _mfn(mfn_x(smfn) & ~0x3UL);
-#endif
-
 #endif
 
     if ( pagetable_get_pfn(v->arch.shadow_table[0]) == mfn_x(smfn)

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