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Commit 575e7c14 authored by Takuya Yoshikawa's avatar Takuya Yoshikawa Committed by Avi Kivity
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KVM: x86 emulator: Disable writeback for CMP emulation 



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: default avatarTakuya Yoshikawa <yoshikawa.takuya@oss.ntt.co.jp>
Signed-off-by: default avatarAvi Kivity <avi@redhat.com>
parent be6d05cf

arch/x86/kvm/emulate.c

+1 −1
Original line number Diff line number Diff line
@@ -3671,6 +3671,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt) 
		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 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt) 
		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;