IB/ipath: Clean up handling of GUID 0

Respond with an error to the SM if our GUID is 0, and don't allow the
user to set our GUID to 0.

Signed-off-by: Bryan O'Sullivan <bryan.osullivan@qlogic.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/ipath/ipath_mad.c b/drivers/infiniband/hw/ipath/ipath_mad.c
index 72d1db8..25908b0 100644
--- a/drivers/infiniband/hw/ipath/ipath_mad.c
+++ b/drivers/infiniband/hw/ipath/ipath_mad.c
@@ -87,7 +87,8 @@
 	struct ipath_devdata *dd = to_idev(ibdev)->dd;
 	u32 vendor, majrev, minrev;
 
-	if (smp->attr_mod)
+	/* GUID 0 is illegal */
+	if (smp->attr_mod || (dd->ipath_guid == 0))
 		smp->status |= IB_SMP_INVALID_FIELD;
 
 	nip->base_version = 1;
@@ -131,10 +132,15 @@
 	 * We only support one GUID for now.  If this changes, the
 	 * portinfo.guid_cap field needs to be updated too.
 	 */
-	if (startgx == 0)
-		/* The first is a copy of the read-only HW GUID. */
-		*p = to_idev(ibdev)->dd->ipath_guid;
-	else
+	if (startgx == 0) {
+		__be64 g = to_idev(ibdev)->dd->ipath_guid;
+		if (g == 0)
+			/* GUID 0 is illegal */
+			smp->status |= IB_SMP_INVALID_FIELD;
+		else
+			/* The first is a copy of the read-only HW GUID. */
+			*p = g;
+	} else
 		smp->status |= IB_SMP_INVALID_FIELD;
 
 	return reply(smp);