diff mbox

[1/7] KVM: x86: Dirty the dest op page on cmpxchg emulation

Message ID 1422257547-4557-2-git-send-email-namit@cs.technion.ac.il (mailing list archive)
State New, archived
Headers show

Commit Message

Nadav Amit Jan. 26, 2015, 7:32 a.m. UTC 
Intel SDM says for CMPXCHG: "To simplify the interface to the processor’s bus,
the destination operand receives a write cycle without regard to the result of
the comparison.". This means the destination page should be dirtied.

Fix it to by writing back the original value if cmpxchg failed.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/kvm/emulate.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)
diff mbox

Patch

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index ef23c1e..aa27254 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2205,12 +2205,15 @@  static int em_cmpxchg(struct x86_emulate_ctxt *ctxt)
 	fastop(ctxt, em_cmp);
 
 	if (ctxt->eflags & EFLG_ZF) {
-		/* Success: write back to memory. */
+		/* Success: write back to memory; no update of EAX */
+		ctxt->src.type = OP_NONE;
 		ctxt->dst.val = ctxt->src.orig_val;
 	} else {
 		/* Failure: write the value we saw to EAX. */
-		ctxt->dst.type = OP_REG;
-		ctxt->dst.addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX);
+		ctxt->src.type = OP_REG;
+		ctxt->src.addr.reg = reg_rmw(ctxt, VCPU_REGS_RAX);
+		ctxt->src.val = ctxt->dst.orig_val;
+		/* Create write-cycle to dest by writing the same value */
 		ctxt->dst.val = ctxt->dst.orig_val;
 	}
 	return X86EMUL_CONTINUE;
@@ -4157,7 +4160,7 @@  static const struct opcode twobyte_table[256] = {
 	F(DstMem | SrcReg | Src2CL | ModRM, em_shrd),
 	GD(0, &group15), F(DstReg | SrcMem | ModRM, em_imul),
 	/* 0xB0 - 0xB7 */
-	I2bv(DstMem | SrcReg | ModRM | Lock | PageTable, em_cmpxchg),
+	I2bv(DstMem | SrcReg | ModRM | Lock | PageTable | SrcWrite, em_cmpxchg),
 	I(DstReg | SrcMemFAddr | ModRM | Src2SS, em_lseg),
 	F(DstMem | SrcReg | ModRM | BitOp | Lock, em_btr),
 	I(DstReg | SrcMemFAddr | ModRM | Src2FS, em_lseg),