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;
         * 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);
 
        struct ipath_devdata *dd = dev_get_drvdata(dev);
        ssize_t ret;
        unsigned short guid[8];
-       __be64 nguid;
+       __be64 new_guid;
        u8 *ng;
        int i;
 
                   &guid[4], &guid[5], &guid[6], &guid[7]) != 8)
                goto invalid;
 
-       ng = (u8 *) &nguid;
+       ng = (u8 *) &new_guid;
 
        for (i = 0; i < 8; i++) {
                if (guid[i] > 0xff)
                ng[i] = guid[i];
        }
 
-       dd->ipath_guid = nguid;
+       if (new_guid == 0)
+               goto invalid;
+
+       dd->ipath_guid = new_guid;
        dd->ipath_nguid = 1;
 
        ret = strlen(buf);