KVM: x86: IN instruction emulation should ignore REP-prefix

The IN instruction is not be affected by REP-prefix as INS is.  Therefore, the
emulation should ignore the REP prefix as well.  The current emulator
implementation tries to perform writeback when IN instruction with REP-prefix
is emulated. This causes it to perform wrong memory write or spurious #GP
exception to be injected to the guest.
Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

arch/x86/kvm/emulate.c

@@ -1324,7 +1324,8 @@ static int pio_in_emulated(struct x86_emulate_ctxt *ctxt,
 		rc->end = n * size;
 	}
 
-	if (ctxt->rep_prefix && !(ctxt->eflags & EFLG_DF)) {
+	if (ctxt->rep_prefix && (ctxt->d & String) &&
+	    !(ctxt->eflags & EFLG_DF)) {
 		ctxt->dst.data = rc->data + rc->pos;
 		ctxt->dst.type = OP_MEM_STR;
 		ctxt->dst.count = (rc->end - rc->pos) / size;