linux-kernel - [PATCH v2] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

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Message-ID: <20251122182929.92634-1-ranxiaokai627@163.com>
Date: Sat, 22 Nov 2025 18:29:29 +0000
From: ranxiaokai627@....com
To: rppt@...nel.org,
	akpm@...ux-foundation.org,
	catalin.marinas@....com,
	changyuanl@...gle.com,
	graf@...zon.com,
	pasha.tatashin@...een.com,
	pratyush@...nel.org
Cc: kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	ran.xiaokai@....com.cn,
	ranxiaokai627@....com
Subject: [PATCH v2] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

From: Ran Xiaokai <ran.xiaokai@....com.cn>

When booting with debug_pagealloc=on while having:
CONFIG_KEXEC_HANDOVER_ENABLE_DEFAULT=y
CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=n
the system fails to boot due to page faults during kmemleak scanning.

This occurs because:
With debug_pagealloc is enabled, __free_pages() invokes
debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for
freed pages in the kernel page table.
Commit 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
triggers this when releases the KHO scratch region calling
init_cma_reserved_pageblock(). Subsequent kmemleak scanning accesses
these non-PRESENT pages, leading to fatal page faults.

Call kmemleak_ignore_phys() from kho_init() to exclude
the reserved region from kmemleak scanning before
it is released to the buddy allocator to fix this.

Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
---
 kernel/liveupdate/kexec_handover.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 224bdf5becb6..c729d455ee7b 100644
--- a/kernel/liveupdate/kexec_handover.c
+++ b/kernel/liveupdate/kexec_handover.c
@@ -11,6 +11,7 @@

 #include <linux/cleanup.h>
 #include <linux/cma.h>
+#include <linux/kmemleak.h>
 #include <linux/count_zeros.h>
 #include <linux/kexec.h>
 #include <linux/kexec_handover.h>
@@ -1369,6 +1370,7 @@ static __init int kho_init(void)
 		unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
 		unsigned long pfn;

+		kmemleak_ignore_phys(kho_scratch[i].addr);
 		for (pfn = base_pfn; pfn < base_pfn + count;
 		     pfn += pageblock_nr_pages)
 			init_cma_reserved_pageblock(pfn_to_page(pfn));
-- 
2.25.1