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

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Message-ID: <20251126072051.546700-1-usamaarif642@gmail.com>
Date: Wed, 26 Nov 2025 07:20:51 +0000
From: Usama Arif <usamaarif642@...il.com>
To: rppt@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Cc: 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] 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_MEMBLOCK_KHO_SCRATCH
is enabled (selected by KHO) and if it is a KHO boot. Add checks
to prevent marking a KHO scratch region unless needed.

kexec_handover.h is now unconditionally included for is_kho_boot.

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 | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/mm/memblock.c b/mm/memblock.c
index e23e16618e9b3..5c85d575bb61c 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -20,8 +20,8 @@
 
 #ifdef CONFIG_KEXEC_HANDOVER
 #include <linux/libfdt.h>
-#include <linux/kexec_handover.h>
 #endif /* CONFIG_KEXEC_HANDOVER */
+#include <linux/kexec_handover.h>
 
 #include <asm/sections.h>
 #include <linux/io.h>
@@ -1126,8 +1126,11 @@ int __init_memblock memblock_reserved_mark_noinit(phys_addr_t base, phys_addr_t
  */
 __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);
+	if (IS_ENABLED(CONFIG_MEMBLOCK_KHO_SCRATCH) && is_kho_boot())
+		return memblock_setclr_flag(&memblock.memory, base, size, 1,
+					    MEMBLOCK_KHO_SCRATCH);
+	else
+		return 0;
 }
 
 /**
@@ -1140,8 +1143,11 @@ __init int memblock_mark_kho_scratch(phys_addr_t base, phys_addr_t size)
  */
 __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);
+	if (IS_ENABLED(CONFIG_MEMBLOCK_KHO_SCRATCH) && is_kho_boot())
+		return memblock_setclr_flag(&memblock.memory, base, size, 0,
+					    MEMBLOCK_KHO_SCRATCH);
+	else
+		return 0;
 }
 
 static bool should_skip_region(struct memblock_type *type,
-- 
2.47.3