kho: skip memoryless NUMA nodes when reserving scratch areas

kho_reserve_scratch() iterates over all online NUMA nodes to allocate
per-node scratch memory.  On systems with memoryless NUMA nodes (nodes
that have CPUs but no memory), memblock_alloc_range_nid() fails because
there is no memory available on that node.  This causes KHO initialization
to fail and kho_enable to be set to false.

Some ARM64 systems have NUMA topologies where certain nodes contain only
CPUs without any associated memory.  These configurations are valid and
should not prevent KHO from functioning.

Fix this by only counting nodes that have memory (N_MEMORY state) and skip
memoryless nodes in the per-node scratch allocation loop.

Link: https://lkml.kernel.org/r/20260120175913.34368-1-epetron@amazon.de
Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers").
Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Alexander Graf <graf@amazon.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index e0a50b012ba36cd24a956364d4a659a1176ed7b9..8a2b2a7e50fc65da591a2c332e72501f9b2dc8bb 100644 (file)
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -655,7 +655,7 @@ static void __init kho_reserve_scratch(void)
        scratch_size_update();
 
        /* FIXME: deal with node hot-plug/remove */
-       kho_scratch_cnt = num_online_nodes() + 2;
+       kho_scratch_cnt = nodes_weight(node_states[N_MEMORY]) + 2;
        size = kho_scratch_cnt * sizeof(*kho_scratch);
        kho_scratch = memblock_alloc(size, PAGE_SIZE);
        if (!kho_scratch) {
@@ -691,7 +691,11 @@ static void __init kho_reserve_scratch(void)
        kho_scratch[i].size = size;
        i++;
 
-       for_each_online_node(nid) {
+       /*
+        * Loop over nodes that have both memory and are online. Skip
+        * memoryless nodes, as we can not allocate scratch areas there.
+        */
+       for_each_node_state(nid, N_MEMORY) {
                size = scratch_size_node(nid);
                addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
                                                0, MEMBLOCK_ALLOC_ACCESSIBLE,