[PATCH v2 5/9] KVM: x86: NOP emulation clears (incorrectly) the high 32-bits of RAX

[Nadav Amit]

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@xxxxxxxxxxxxxxxxx>
---
 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

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