[PATCH 6.18.y 2/2] kho: make sure scratch size is always aligned by CMA_MIN_ALIGNMENT_BYTES

[Sasha Levin <sashal@kernel.org>]

From: "Pratyush Yadav (Google)" <pratyush@kernel.org>

[ Upstream commit 0e39380a7316122e1b00012b3f3cd3e318b3e7d3 ]

When using scratch_scale, the scratch sizes are rounded up to
CMA_MIN_ALIGNMENT_BYTES since they will be released as MIGRATE_CMA. This
is not done when using fixed scratch sizes via command line. This can
result in user specifying a size which is not aligned, and thus kernel
releasing a pageblock that is only partially scratch.

Do the rounding up for both cases in scratch_size_update().

Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
Cc: stable@kernel.org
Signed-off-by: Pratyush Yadav (Google) <pratyush@kernel.org>
Link: https://patch.msgid.link/20260519160554.2713361-1-pratyush@kernel.org
Signed-off-by: Pasha Tatashin <pasha.tatashin@soleen.com>
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/kexec_handover.c | 32 +++++++++++++++++++++-----------
 1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/kernel/kexec_handover.c b/kernel/kexec_handover.c
index 37e6048118e8b7..bd10660db469a2 100644
--- a/kernel/kexec_handover.c
+++ b/kernel/kexec_handover.c
@@ -569,20 +569,30 @@ early_param("kho_scratch", kho_parse_scratch_size);
 
 static void __init scratch_size_update(void)
 {
-	phys_addr_t size;
+	/*
+	 * If fixed sizes are not provided via command line, calculate them
+	 * now.
+	 */
+	if (scratch_scale) {
+		phys_addr_t size;
 
-	if (!scratch_scale)
-		return;
+		size = memblock_reserved_kern_size(ARCH_LOW_ADDRESS_LIMIT,
+						   NUMA_NO_NODE);
+		size = size * scratch_scale / 100;
+		scratch_size_lowmem = size;
 
-	size = memblock_reserved_kern_size(ARCH_LOW_ADDRESS_LIMIT,
-					   NUMA_NO_NODE);
-	size = size * scratch_scale / 100;
-	scratch_size_lowmem = round_up(size, CMA_MIN_ALIGNMENT_BYTES);
+		size = memblock_reserved_kern_size(MEMBLOCK_ALLOC_ANYWHERE,
+						   NUMA_NO_NODE);
+		size = size * scratch_scale / 100 - scratch_size_lowmem;
+		scratch_size_global = size;
+	}
 
-	size = memblock_reserved_kern_size(MEMBLOCK_ALLOC_ANYWHERE,
-					   NUMA_NO_NODE);
-	size = size * scratch_scale / 100 - scratch_size_lowmem;
-	scratch_size_global = round_up(size, CMA_MIN_ALIGNMENT_BYTES);
+	/*
+	 * Scratch areas are released as MIGRATE_CMA. Round them up to the right
+	 * size.
+	 */
+	scratch_size_lowmem = round_up(scratch_size_lowmem, CMA_MIN_ALIGNMENT_BYTES);
+	scratch_size_global = round_up(scratch_size_global, CMA_MIN_ALIGNMENT_BYTES);
 }
 
 static phys_addr_t __init scratch_size_node(int nid)
-- 
2.53.0