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: 63db8170bf34 (“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>

diff --git a/drivers/acpi/numa/srat.c b/drivers/acpi/numa/srat.c
index 59fffe34c9d041130695a7b06f6a60aa8ad8c143..00ac0d7bb8c9f99aeb3b0250388c1892969da99b 100644 (file)
--- a/drivers/acpi/numa/srat.c
+++ b/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;