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@xxxxxxxxxxxxxx> --- arch/x86/kvm/mmu.c | 8 ++++++++ 1 files changed, 8 insertions(+), 0 deletions(-) diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 2328ee6..bb55b15 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -3597,6 +3597,14 @@ 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 (sp->role.level == 1 && !(offset & (pte_size - 1)) && bytes == 1) + return false; + misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1); misaligned |= bytes < 4; -- 1.7.5.4 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
