From 5d9ca30e96f567b67a36727aa4ebb34911a2b84a Mon Sep 17 00:00:00 2001 From: Xiao Guangrong Date: Thu, 22 Sep 2011 16:57:55 +0800 Subject: [PATCH] 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 Signed-off-by: Avi Kivity --- arch/x86/kvm/mmu.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 986aea55366b..ca6f72ab4c3b 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -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; -- 2.20.1