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 <[email protected]> Signed-off-by: Marcelo Tosatti <[email protected]>
glzhao · Sep 25, 2011 · caa8a16 · caa8a16
1 parent c61fa9d
commit caa8a16
Showing 1 changed file with 4 additions and 0 deletions.
diff --git 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;
 }