diff mbox

[v2,2/9] KVM: x86: Wrong emulation on 'xadd X, X'

Message ID 1403101166-23616-3-git-send-email-namit@cs.technion.ac.il (mailing list archive)
State New, archived
Headers show

Commit Message

Nadav Amit June 18, 2014, 2:19 p.m. UTC 
The emulator does not emulate the xadd instruction correctly if the two
operands are the same.  In this (unlikely) situation the result should be the
sum of X and X (2X) when it is currently X.  The solution is to first perform
writeback to the source, before writing to the destination.  The only
instruction which should be affected is xadd, as the other instructions that
perform writeback to the source use the extended accumlator (e.g., RAX:RDX).

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
---
 arch/x86/kvm/emulate.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)
diff mbox

Patch

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index f0b0a10..3c8d867 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4711,17 +4711,17 @@  special_insn:
 		goto done;
 
 writeback:
-	if (!(ctxt->d & NoWrite)) {
-		rc = writeback(ctxt, &ctxt->dst);
-		if (rc != X86EMUL_CONTINUE)
-			goto done;
-	}
 	if (ctxt->d & SrcWrite) {
 		BUG_ON(ctxt->src.type == OP_MEM || ctxt->src.type == OP_MEM_STR);
 		rc = writeback(ctxt, &ctxt->src);
 		if (rc != X86EMUL_CONTINUE)
 			goto done;
 	}
+	if (!(ctxt->d & NoWrite)) {
+		rc = writeback(ctxt, &ctxt->dst);
+		if (rc != X86EMUL_CONTINUE)
+			goto done;
+	}
 
 	/*
 	 * restore dst type in case the decoding will be reused