[Xen-changelog] [xen-unstable] [XEN] Fix the "early unshadow" optimization to look at the entire pte.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User George Dunlap <dunlapg@xxxxxxxxx>
# Node ID 680b37789200cca3f076b5be623a7423e64711cb
# Parent  ade94aa072c51e7b0834405569436ab1eb334d9a
[XEN] Fix the "early unshadow" optimization to look at the entire pte.

The optimization is designed to detect pagetable destruction, but re-uses the
pagetable entries to store data under certain conditions (paging, zeroing, &c);
sometimes the lower 8 bits are 0.  These "false positives" cause unnecessary
shadowing and unshadowing.

Signed-off-by: George Dunlap <gdunlap@xxxxxxxxxxxxx>
---
 xen/arch/x86/mm/shadow/multi.c |    2 +-
 1 files changed, 1 insertion(+), 1 deletion(-)

diff -r ade94aa072c5 -r 680b37789200 xen/arch/x86/mm/shadow/multi.c
--- a/xen/arch/x86/mm/shadow/multi.c    Tue Nov 14 11:57:53 2006 +0000
+++ b/xen/arch/x86/mm/shadow/multi.c    Tue Nov 14 11:21:26 2006 -0500
@@ -3778,7 +3778,7 @@ sh_x86_emulate_write(struct vcpu *v, uns
         shadow_validate_guest_pt_write(v, mfn, addr, bytes_on_page);
         bytes -= bytes_on_page;
         /* If we are writing zeros to this page, might want to unshadow */
-        if ( *(u8 *)addr == 0 )
+        if ( *(u32 *)addr == 0 )
             check_for_early_unshadow(v, mfn);
         sh_unmap_domain_page(addr);
     }

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