kho: do not reserve empty per-node bootmem areas

Some nodes do not allocate any early boot memory. An example is
hotpluggable nodes with movable_node enabled. So the bootmem size for
them ends up being zero.

Zero size allocations normally don't play well with memblock. Memblock
returns an address, but then doesn't actually reserve anything. This
address ends up being recorded in kho_bootmem with a size of 0. In case
of hotpluggable nodes with movable_nodes, the allocation on the node
actually fails because memblock refuses to allocate there, and so KHO
fails to initialize.

Skip bootmem reservation for such nodes entirely.

To keep the code more robust, avoid overloading kho_bootmem_cnt. use
max_nr_bootmem to store the size of kho_bootmem array. This ensures that
the location of kho_bootmem_cnt assignment does not affect the cleanup
paths.

Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
Reported-by: Bing Jiao <bingjiao@google.com>
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Link: https://patch.msgid.link/20261014131547.259138-1-pratyush@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

1 files changed, 13 insertions, 4 deletions

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 7018e25e4eda..6f1f55fe3181 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -831,8 +831,8 @@ bool kho_bootmem_overlap(phys_addr_t phys, size_t size)
  */
 static void __init kho_reserve_bootmem(void)
 {
+	int nid, i = 0, max_nr_bootmem;
 	phys_addr_t addr, size;
-	int nid, i = 0;
 
 	if (!kho_enable)
 		return;
@@ -840,8 +840,8 @@ static void __init kho_reserve_bootmem(void)
 	bootmem_size_update();
 
 	/* FIXME: deal with node hot-plug/remove */
-	kho_bootmem_cnt = nodes_weight(node_states[N_MEMORY]) + 2;
-	size = kho_bootmem_cnt * sizeof(*kho_bootmem);
+	max_nr_bootmem = nodes_weight(node_states[N_MEMORY]) + 2;
+	size = max_nr_bootmem * sizeof(*kho_bootmem);
 	kho_bootmem = memblock_alloc(size, PAGE_SIZE);
 	if (!kho_bootmem) {
 		pr_err("Failed to reserve bootmem array\n");
@@ -882,6 +882,9 @@ static void __init kho_reserve_bootmem(void)
 	 */
 	for_each_node_state(nid, N_MEMORY) {
 		size = bootmem_size_node(nid);
+		if (!size)
+			continue;
+
 		addr = memblock_alloc_range_nid(size, BOOTMEM_ALIGNMENT_BYTES,
 						0, MEMBLOCK_ALLOC_ACCESSIBLE,
 						nid, true);
@@ -895,13 +898,19 @@ static void __init kho_reserve_bootmem(void)
 		i++;
 	}
 
+	/*
+	 * Nodes that needed no bootmem were skipped, so fewer areas than
+	 * initially estimated may have been reserved.
+	 */
+	kho_bootmem_cnt = i;
+
 	return;
 
 err_free_bootmem_areas:
 	for (i--; i >= 0; i--)
 		memblock_phys_free(kho_bootmem[i].addr, kho_bootmem[i].size);
 err_free_bootmem_desc:
-	memblock_free(kho_bootmem, kho_bootmem_cnt * sizeof(*kho_bootmem));
+	memblock_free(kho_bootmem, max_nr_bootmem * sizeof(*kho_bootmem));
 err_disable_kho:
 	pr_warn("Failed to reserve bootmem, disabling kexec handover\n");
 	kho_enable = false;