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KVM: MMU: fix detecting misaligned accessed 

Sometimes, we only modify the last one byte of a pte to update status bit,
for example, clear_bit is used to clear r/w bit in linux kernel and 'andb'
instruction is used in this function, in this case, kvm_mmu_pte_write will
treat it as misaligned access, and the shadow page table is zapped

Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Xiao Guangrong 2011-09-22 16:57:55 +08:00 committed by Avi Kivity
parent 889e5cbced
commit 5d9ca30e96
1 changed files with 8 additions and 0 deletions
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8
arch/x86/kvm/mmu.c
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@ -3602,6 +3602,14 @@ static bool detect_write_misaligned(struct kvm_mmu_page *sp, gpa_t gpa,
offset = offset_in_page(gpa);
pte_size = sp->role.cr4_pae ? 8 : 4;
/*
* Sometimes, the OS only writes the last one bytes to update status
* bits, for example, in linux, andb instruction is used in clear_bit().
*/
if (!(offset & (pte_size - 1)) && bytes == 1)
return false;
misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1);
misaligned |= bytes < 4;