xen: issue warning message when out of grant maptrack entries

When a driver domain (e.g. dom0) is running out of maptrack entries it
can't map any more foreign domain pages. Instead of silently stalling
the affected domUs issue a rate limited warning in this case in order
to make it easier to detect that situation.
Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

drivers/xen/grant-table.c

@@ -1040,18 +1040,33 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
 		return ret;
 
 	for (i = 0; i < count; i++) {
-		/* Retry eagain maps */
-		if (map_ops[i].status == GNTST_eagain)
-			gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref, map_ops + i,
-						&map_ops[i].status, __func__);
-
-		if (map_ops[i].status == GNTST_okay) {
+		switch (map_ops[i].status) {
+		case GNTST_okay:
+		{
 			struct xen_page_foreign *foreign;
 
 			SetPageForeign(pages[i]);
 			foreign = xen_page_foreign(pages[i]);
 			foreign->domid = map_ops[i].dom;
 			foreign->gref = map_ops[i].ref;
+			break;
+		}
+
+		case GNTST_no_device_space:
+			pr_warn_ratelimited("maptrack limit reached, can't map all guest pages\n");
+			break;
+
+		case GNTST_eagain:
+			/* Retry eagain maps */
+			gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref,
+						map_ops + i,
+						&map_ops[i].status, __func__);
+			/* Test status in next loop iteration. */
+			i--;
+			break;
+
+		default:
+			break;
 		}
 	}