Re: [PATCH v3] KHO: Fix boot failure due to kmemleak access to non-PRESENT pages

[Pratyush Yadav <pratyush@kernel.org>]

On Mon, Nov 24 2025, Pratyush Yadav wrote:

> On Mon, Nov 24 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>
>> ---
>>  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);
>
> Can you please put the explanation you gave in [0] for why this is not
> necessary in KHO boot as a comment here?

And also an explanation of why this is necessary in the first place. You
do explain that in the commit message, but a shorter version as a
comment will make this a lot easier to understand instead of having to
dig through git history.

[...]

-- 
Regards,
Pratyush Yadav