[PATCH v2 2/3] kho: skip zero-sized lowmem and global bootmem areas

["Mike Rapoport (Microsoft)" <rppt@kernel.org>]

The lowmem and the global bootmem areas can have zero size, for example
when none or all of the memory is below ARCH_LOW_ADDRESS_LIMIT, or when
either of those areas is explicitly set to zero with kho_bootmem=.

For a zero-sized allocation memblock returns an address without reserving
anything, and that empty area is recorded in kho_bootmem. If there is no
memory below ARCH_LOW_ADDRESS_LIMIT, allocation of the empty lowmem area
fails and KHO gets disabled.

Extract a helper that checks for zero size and allocates memory from
memblock, and use it to skip empty areas the same way as empty per-node
areas are skipped.

Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
Reported-by: Chen Pei <cp0613@linux.alibaba.com>
Closes: https://lore.kernel.org/all/20261026131851.9942-1-cp0613@linux.alibaba.com
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 66 +++++++++++++++++---------------------
 1 file changed, 30 insertions(+), 36 deletions(-)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 2ac5d94f33fd4..5b1797d1289c8 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -829,6 +829,26 @@ static int __init kho_bootmem_cmp(const void *_a, const void *_b)
 	return cmp_int(a->addr, b->addr);
 }
 
+static int __init kho_reserve_bootmem_area(phys_addr_t size, phys_addr_t end,
+					   int nid)
+{
+	phys_addr_t addr;
+
+	if (!size)
+		return 0;
+
+	addr = memblock_alloc_range_nid(size, BOOTMEM_ALIGNMENT_BYTES, 0, end,
+					nid, true);
+	if (!addr)
+		return -ENOMEM;
+
+	kho_bootmem[kho_bootmem_cnt].addr = addr;
+	kho_bootmem[kho_bootmem_cnt].size = size;
+	kho_bootmem_cnt++;
+
+	return 0;
+}
+
 /**
  * kho_reserve_bootmem - Reserve a contiguous chunk of memory for kexec
  *
@@ -840,8 +860,8 @@ static int __init kho_bootmem_cmp(const void *_a, const void *_b)
  */
 static void __init kho_reserve_bootmem(void)
 {
-	int nid, i = 0, max_nr_bootmem;
-	phys_addr_t addr, size;
+	int nid, max_nr_bootmem;
+	phys_addr_t size;
 
 	if (!kho_enable)
 		return;
@@ -861,66 +881,40 @@ static void __init kho_reserve_bootmem(void)
 	 * reserve bootmem area in low memory for lowmem allocations in the
 	 * next kernel
 	 */
-	size = bootmem_size_lowmem;
-	addr = memblock_phys_alloc_range(size, BOOTMEM_ALIGNMENT_BYTES, 0,
-					 ARCH_LOW_ADDRESS_LIMIT);
-	if (!addr) {
+	if (kho_reserve_bootmem_area(bootmem_size_lowmem, ARCH_LOW_ADDRESS_LIMIT,
+				     NUMA_NO_NODE)) {
 		pr_err("Failed to reserve lowmem bootmem\n");
 		goto err_free_bootmem_desc;
 	}
 
-	kho_bootmem[i].addr = addr;
-	kho_bootmem[i].size = size;
-	i++;
-
 	/* reserve large contiguous area for allocations without nid */
-	size = bootmem_size_global;
-	addr = memblock_phys_alloc(size, BOOTMEM_ALIGNMENT_BYTES);
-	if (!addr) {
+	if (kho_reserve_bootmem_area(bootmem_size_global,
+				     MEMBLOCK_ALLOC_ACCESSIBLE, NUMA_NO_NODE)) {
 		pr_err("Failed to reserve global bootmem\n");
 		goto err_free_bootmem_areas;
 	}
 
-	kho_bootmem[i].addr = addr;
-	kho_bootmem[i].size = size;
-	i++;
-
 	/*
 	 * Loop over nodes that have both memory and are online. Skip
 	 * memoryless nodes, as we can not allocate bootmem areas there.
 	 */
 	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);
-		if (!addr) {
+		if (kho_reserve_bootmem_area(bootmem_size_node(nid),
+					     MEMBLOCK_ALLOC_ACCESSIBLE, nid)) {
 			pr_err("Failed to reserve nid %d bootmem\n", nid);
 			goto err_free_bootmem_areas;
 		}
-
-		kho_bootmem[i].addr = addr;
-		kho_bootmem[i].size = size;
-		i++;
 	}
 
-	/*
-	 * Nodes that needed no bootmem were skipped, so fewer areas than
-	 * initially estimated may have been reserved.
-	 */
-	kho_bootmem_cnt = i;
-
 	sort(kho_bootmem, kho_bootmem_cnt, sizeof(*kho_bootmem),
 	     kho_bootmem_cmp, NULL);
 
 	return;
 
 err_free_bootmem_areas:
-	for (i--; i >= 0; i--)
+	for (int i = kho_bootmem_cnt - 1; i >= 0; i--)
 		memblock_phys_free(kho_bootmem[i].addr, kho_bootmem[i].size);
+	kho_bootmem_cnt = 0;
 err_free_bootmem_desc:
 	memblock_free(kho_bootmem, max_nr_bootmem * sizeof(*kho_bootmem));
 err_disable_kho:

-- 
2.53.0