[PATCH 5/6] KVM: x86: NOP emulation clears (incorrectly) the high 32-bits of RAX

Nadav Amit
2014-06-15T13:13:01Z

On long-mode the current NOP (0x90) emulation still writes back to RAX. As a
result, EAX is zero-extended and the high 32-bits of RAX are cleared.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
arch/x86/kvm/emulate.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index b354531..eb93eb4 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4663,8 +4663,9 @@ special_insn:
break;
case 0x90 ... 0x97: /* nop / xchg reg, rax */
if (ctxt->dst.addr.reg == reg_rmw(ctxt, VCPU_REGS_RAX))
- break;
- rc = em_xchg(ctxt);
+ ctxt->dst.type = OP_NONE;
+ else
+ rc = em_xchg(ctxt);
break;
case 0x98: /* cbw/cwde/cdqe */
switch (ctxt->op_bytes) {
--
1.9.1