KVM: fix sil/dil/bpl/spl in the mod/rm fields

The x86-64 extended low-byte registers were fetched correctly from reg,
but not from mod/rm.

This fixes another bug in the boot of RHEL5.9 64-bit, but it is still
not enough.

Cc: <stable@vger.kernel.org> # 3.9
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/x86/kvm/emulate.c

@@ -1240,9 +1240,12 @@ static int decode_modrm(struct x86_emulate_ctxt *ctxt,
 	ctxt->modrm_seg = VCPU_SREG_DS;
 
 	if (ctxt->modrm_mod == 3) {
+		int highbyte_regs = ctxt->rex_prefix == 0;
+
 		op->type = OP_REG;
 		op->bytes = (ctxt->d & ByteOp) ? 1 : ctxt->op_bytes;
-		op->addr.reg = decode_register(ctxt, ctxt->modrm_rm, ctxt->d & ByteOp);
+		op->addr.reg = decode_register(ctxt, ctxt->modrm_rm,
+					       highbyte_regs && (ctxt->d & ByteOp));
 		if (ctxt->d & Sse) {
 			op->type = OP_XMM;
 			op->bytes = 16;