linux-kernel - [PATCH v2 2/2] mm/memblock: only mark/clear KHO scratch memory when needed

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Message-ID: <20251127203724.3177621-3-usamaarif642@gmail.com>
Date: Thu, 27 Nov 2025 20:33:20 +0000
From: Usama Arif <usamaarif642@...il.com>
To: rppt@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: kas@...nel.org,
	changyuanl@...gle.com,
	graf@...zon.com,
	leitao@...ian.org,
	thevlad@...a.com,
	pratyush@...nel.org,
	dave.hansen@...ux.intel.com,
	linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	Usama Arif <usamaarif642@...il.com>
Subject: [PATCH v2 2/2] mm/memblock: only mark/clear KHO scratch memory when needed

The scratch memory for kexec handover is used to bootstrap the
kexec'ed kernel. It is only needed when CONFIG_KEXEC_HANDOVER
is enabled and only if it is a KHO boot. Add checks to prevent
marking a KHO scratch region unless needed.

Fixes: a2daf83e10378 ("x86/e820: temporarily enable KHO scratch for memory below 1M")
Reported-by: Vlad Poenaru <thevlad@...a.com>
Signed-off-by: Usama Arif <usamaarif642@...il.com>
---
 mm/memblock.c | 74 ++++++++++++++++++++++++++++++---------------------
 1 file changed, 44 insertions(+), 30 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index 8b13d5c28922a..8a2cebcfe0a18 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -1114,36 +1114,6 @@ int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t
 				    MEMBLOCK_RSRV_NOINIT);
 }
 
-/**
- * memblock_mark_kho_scratch - Mark a memory region as MEMBLOCK_KHO_SCRATCH.
- * @base: the base phys addr of the region
- * @size: the size of the region
- *
- * Only memory regions marked with %MEMBLOCK_KHO_SCRATCH will be considered
- * for allocations during early boot with kexec handover.
- *
- * Return: 0 on success, -errno on failure.
- */
-__init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
-{
-	return memblock_setclr_flag(&memblock.memory, base, size, 1,
-				    MEMBLOCK_KHO_SCRATCH);
-}
-
-/**
- * memblock_clear_kho_scratch - Clear MEMBLOCK_KHO_SCRATCH flag for a
- * specified region.
- * @base: the base phys addr of the region
- * @size: the size of the region
- *
- * Return: 0 on success, -errno on failure.
- */
-__init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
-{
-	return memblock_setclr_flag(&memblock.memory, base, size, 0,
-				    MEMBLOCK_KHO_SCRATCH);
-}
-
 static bool should_skip_region(struct memblock_type *type,
 			       struct memblock_region *m,
 			       int nid, int flags)
@@ -2617,12 +2587,56 @@ static bool __init reserve_mem_kho_revive(const char *name, phys_addr_t size,
 
 	return true;
 }
+
+/**
+ * memblock_mark_kho_scratch - Mark a memory region as MEMBLOCK_KHO_SCRATCH.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Only memory regions marked with %MEMBLOCK_KHO_SCRATCH will be considered
+ * for allocations during early boot with kexec handover.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+__init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
+{
+	if (is_kho_boot())
+		return memblock_setclr_flag(&memblock.memory, base, size, 1,
+					    MEMBLOCK_KHO_SCRATCH);
+	return 0;
+}
+
+/**
+ * memblock_clear_kho_scratch - Clear MEMBLOCK_KHO_SCRATCH flag for a
+ * specified region.
+ * @base: the base phys addr of the region
+ * @size: the size of the region
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+__init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
+{
+	if (is_kho_boot())
+		return memblock_setclr_flag(&memblock.memory, base, size, 0,
+					    MEMBLOCK_KHO_SCRATCH);
+	return 0;
+}
 #else
 static bool __init reserve_mem_kho_revive(const char *name, phys_addr_t size,
 					  phys_addr_t align)
 {
 	return false;
 }
+
+__init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
+{
+	return 0;
+}
+
+__init int memblock_clear_kho_scratch(phys_addr_t base, phys_addr_t size)
+{
+	return 0;
+}
 #endif /* CONFIG_KEXEC_HANDOVER */
 
 /*
-- 
2.47.3