From caa8a168e35650961b9b0d43b9b6fc2279351949 Mon Sep 17 00:00:00 2001 From: Avi Kivity Date: Sun, 11 Sep 2011 11:23:02 +0300 Subject: [PATCH] KVM: x86 emulator: disable writeback for TEST The TEST instruction doesn't write its destination operand. This could cause problems if an MMIO register was accessed using the TEST instruction. Recently Windows XP was observed to use TEST against the APIC ICR; this can cause spurious IPIs. Signed-off-by: Avi Kivity Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/emulate.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index e10fd3732d10..af06539369b4 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -1670,6 +1670,8 @@ static int em_grp3(struct x86_emulate_ctxt *ctxt) switch (ctxt->modrm_reg) { case 0 ... 1: /* test */ emulate_2op_SrcV(ctxt, "test"); + /* Disable writeback. */ + ctxt->dst.type = OP_NONE; break; case 2: /* not */ ctxt->dst.val = ~ctxt->dst.val; @@ -2513,6 +2515,8 @@ static int em_cmp(struct x86_emulate_ctxt *ctxt) static int em_test(struct x86_emulate_ctxt *ctxt) { emulate_2op_SrcV(ctxt, "test"); + /* Disable writeback. */ + ctxt->dst.type = OP_NONE; return X86EMUL_CONTINUE; } -- 2.34.1