mm/fake-numa: handle cases with no SRAT info

Handle more gracefully cases where no SRAT information is available, like
in VMs with no Numa support, and allow fake-numa configuration to complete
successfully in these cases

Link: https://lkml.kernel.org/r/20250127171623.1523171-1-bfaccini@nvidia.com
Fixes: 63db817 (“mm/fake-numa: allow later numa node hotplug”)
Signed-off-by: Bruno Faccini <bfaccini@nvidia.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Hyeonggon Yoo <hyeonggon.yoo@sk.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Len Brown <lenb@kernel.org>
Cc: "Mike Rapoport (IBM)" <rppt@kernel.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: bfaccini

drivers/acpi/numa/srat.c

@@ -95,9 +95,13 @@ int __init fix_pxm_node_maps(int max_nid)
 	int i, j, index = -1, count = 0;
 	nodemask_t nodes_to_enable;
 
-	if (numa_off || srat_disabled())
+	if (numa_off)
 		return -1;
 
+	/* no or incomplete node/PXM mapping set, nothing to do */
+	if (srat_disabled())
+		return 0;
+
 	/* find fake nodes PXM mapping */
 	for (i = 0; i < MAX_NUMNODES; i++) {
 		if (node_to_pxm_map[i] != PXM_INVAL) {
@@ -117,6 +121,11 @@ int __init fix_pxm_node_maps(int max_nid)
 			}
 		}
 	}
+	if (index == -1) {
+		pr_debug("No node/PXM mapping has been set\n");
+		/* nothing more to be done */
+		return 0;
+	}
 	if (WARN(index != max_nid, "%d max nid  when expected %d\n",
 		      index, max_nid))
 		return -1;