Commit 5d9ca30e authored Sep 22, 2011 by Xiao Guangrong Committed by Avi Kivity Dec 27, 2011

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>

parent 889e5cbc

arch/x86/kvm/mmu.c

+8 −0

Original line number	Diff line number	Diff line
		@@ -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;

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