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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 <avi@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Avi Kivity 2011-09-11 11:23:02 +03:00
parent c61fa9d63b
commit caa8a168e3
1 changed files with 4 additions and 0 deletions
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4
arch/x86/kvm/emulate.c
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@ -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;
}