[PATCH v4] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[PATCH v4] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[ranxiaokai627]

From: Ran Xiaokai <ran.xiaokai@zte.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.
KHO scratch areas are allocated from memblock and noted by kmemleak. But
these areas don't remain reserved but released later to the page allocator
using init_cma_reserved_pageblock(). This causes subsequent kmemleak scans
access non-PRESENT pages, leading to fatal page faults.

Mark scratch areas with kmemleak_ignore_phys() after they are allocated
from memblock to exclude them from kmemleak scanning before they are
released to buddy allocator to fix this.

Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
---
 kernel/liveupdate/kexec_handover.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
index 224bdf5becb6..55d66e65274f 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 +1370,15 @@ static __init int kho_init(void)
 		unsigned long count = kho_scratch[i].size >> PAGE_SHIFT;
 		unsigned long pfn;
 
+		/*
+		 * When debug_pagealloc is enabled, __free_pages() clears the
+		 * corresponding PRESENT bit in the kernel page table.
+		 * Subsequent kmemleak scans of these pages cause the
+		 * non-PRESENT page faults.
+		 * Mark scratch areas with kmemleak_ignore_phys() to exclude
+		 * them from kmemleak scanning.
+		 */
+		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

Re: [PATCH v4] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[Pratyush Yadav]

On Thu, Nov 27 2025, ranxiaokai627@163.com wrote:

> From: Ran Xiaokai <ran.xiaokai@zte.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.
> KHO scratch areas are allocated from memblock and noted by kmemleak. But
> these areas don't remain reserved but released later to the page allocator
> using init_cma_reserved_pageblock(). This causes subsequent kmemleak scans
> access non-PRESENT pages, leading to fatal page faults.
>
> Mark scratch areas with kmemleak_ignore_phys() after they are allocated
> from memblock to exclude them from kmemleak scanning before they are
> released to buddy allocator to fix this.
>
> Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
> Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Reviewed-by: Pratyush Yadav <pratyush@kernel.org>

Thanks!

[...]

-- 
Regards,
Pratyush Yadav