[PATCH] kho: skip memoryless NUMA nodes when reserving scratch areas

[Evangelos Petrongonas <epetron@amazon.de>]

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 introducing kho_mem_nodes_count() which counts only nodes
that have memory (N_MEMORY state), and skip memoryless nodes in the
per-node scratch allocation loop.

Signed-off-by: Evangelos Petrongonas <epetron@amazon.de>
---
 kernel/liveupdate/kexec_handover.c | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 9dc51fab604f..c970ed08b477 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -623,6 +623,23 @@ static phys_addr_t __init scratch_size_node(int nid)
 	return round_up(size, CMA_MIN_ALIGNMENT_BYTES);
 }
 
+/*
+ * Count online NUMA nodes that have memory. Memoryless nodes cannot have
+ * scratch memory and should be excluded.
+ */
+static unsigned int __init kho_mem_nodes_count(void)
+{
+	unsigned int cnt = 0;
+	int nid;
+
+	for_each_online_node(nid) {
+		if (node_state(nid, N_MEMORY))
+			cnt++;
+	}
+
+	return cnt;
+}
+
 /**
  * kho_reserve_scratch - Reserve a contiguous chunk of memory for kexec
  *
@@ -643,7 +660,7 @@ 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 = kho_mem_nodes_count() + 2;
 	size = kho_scratch_cnt * sizeof(*kho_scratch);
 	kho_scratch = memblock_alloc(size, PAGE_SIZE);
 	if (!kho_scratch)
@@ -674,6 +691,10 @@ static void __init kho_reserve_scratch(void)
 	i++;
 
 	for_each_online_node(nid) {
+		/* Skip memoryless nodes - we cannot allocate scratch memory there */
+		if (!node_state(nid, N_MEMORY))
+			continue;
+
 		size = scratch_size_node(nid);
 		addr = memblock_alloc_range_nid(size, CMA_MIN_ALIGNMENT_BYTES,
 						0, MEMBLOCK_ALLOC_ACCESSIBLE,
-- 
2.43.0




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