linux-kernel - [PATCH 4/6] KVM: x86: emulation of dword cmov on long-mode should clear [63:32]

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Date:	Sun, 15 Jun 2014 16:13:00 +0300
From:	Nadav Amit <namit@...technion.ac.il>
To:	pbonzini@...hat.com
Cc:	gleb@...nel.org, tglx@...utronix.de, mingo@...hat.com,
	hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, Nadav Amit <namit@...technion.ac.il>
Subject: [PATCH 4/6] KVM: x86: emulation of dword cmov on long-mode should clear [63:32]

Even if the condition of cmov is not satisfied, bits[63:32] should be cleared.
This is clearly stated in Intel's CMOVcc documentation.  The solution is to
reassign the destination onto itself if the condition is unsatisfied.  For that
matter the original destination value needs to be read.

Signed-off-by: Nadav Amit <namit@...technion.ac.il>
---
 arch/x86/kvm/emulate.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0183350..b354531 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -3905,7 +3905,7 @@ static const struct opcode twobyte_table[256] = {
 	N, N,
 	N, N, N, N, N, N, N, N,
 	/* 0x40 - 0x4F */
-	X16(D(DstReg | SrcMem | ModRM | Mov)),
+	X16(D(DstReg | SrcMem | ModRM)),
 	/* 0x50 - 0x5F */
 	N, N, N, N, N, N, N, N, N, N, N, N, N, N, N, N,
 	/* 0x60 - 0x6F */
@@ -4799,8 +4799,10 @@ twobyte_insn:
 		ops->get_dr(ctxt, ctxt->modrm_reg, &ctxt->dst.val);
 		break;
 	case 0x40 ... 0x4f:	/* cmov */
-		ctxt->dst.val = ctxt->dst.orig_val = ctxt->src.val;
-		if (!test_cc(ctxt->b, ctxt->eflags))
+		if (test_cc(ctxt->b, ctxt->eflags))
+			ctxt->dst.val = ctxt->src.val;
+		else if (ctxt->mode != X86EMUL_MODE_PROT64 ||
+			 ctxt->op_bytes != 4)
 			ctxt->dst.type = OP_NONE; /* no writeback */
 		break;
 	case 0x80 ... 0x8f: /* jnz rel, etc*/
-- 
1.9.1

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