From: Nadav Amit <namit@cs.technion.ac.il>
Date: Sun, 15 Jun 2014 13:13:01 +0000 (+0300)
Subject: KVM: x86: NOP emulation clears (incorrectly) the high 32-bits of RAX
X-Git-Url: https://git.karo-electronics.de/?a=commitdiff_plain;h=a825f5cc4a8455663562809748240169cb9bc2c0;p=linux-beck.git

KVM: x86: NOP emulation clears (incorrectly) the high 32-bits of RAX

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>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 6f09b2e555ef..84dc4ba0364d 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4688,8 +4688,9 @@ 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) {