diff mbox

[1/3,v2] KVM: x86 emulator: Disable writeback for CMP emulation

Message ID 20110413002455.f2160cd3.takuya.yoshikawa@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Takuya Yoshikawa April 12, 2011, 3:24 p.m. UTC 
From: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>

This stops "CMP r/m, reg" to write back the data into memory.
Pointed out by Avi.

The writeback suppression now covers CMP, CMPS, SCAS.

Signed-off-by: Takuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
---
 Changelog v1->v2: moved the line just after the cmp label.

 arch/x86/kvm/emulate.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

Comments

Avi Kivity April 13, 2011, 11:08 a.m. UTC | #1 
On 04/12/2011 06:24 PM, Takuya Yoshikawa wrote:
> From: Takuya Yoshikawa<yoshikawa.takuya@oss.ntt.co.jp>
>
> This stops "CMP r/m, reg" to write back the data into memory.
> Pointed out by Avi.
>
> The writeback suppression now covers CMP, CMPS, SCAS.
>

Patchset looks good, nice cleanup.
diff mbox

Patch

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 3e8b4ab..db48e91 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3671,6 +3671,7 @@  special_insn:
 		break;
 	case 0x38 ... 0x3d:
 	      cmp:		/* cmp */
+		c->dst.type = OP_NONE; /* Disable writeback. */
 		emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags);
 		break;
 	case 0x40 ... 0x47: /* inc r16/r32 */
@@ -3797,7 +3798,6 @@  special_insn:
 		rc = emulate_popf(ctxt, ops, &c->dst.val, c->op_bytes);
 		break;
 	case 0xa6 ... 0xa7:	/* cmps */
-		c->dst.type = OP_NONE; /* Disable writeback. */
 		goto cmp;
 	case 0xa8 ... 0xa9:	/* test ax, imm */
 		goto test;