linux-kernel - Re: [PATCH 2/2] liveupdate: Fix boot failure due to kmemleak access to unmapped pages

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Message-ID: <20251122180720.92605-1-ranxiaokai627@163.com>
Date: Sat, 22 Nov 2025 18:07:20 +0000
From: ranxiaokai627@....com
To: rppt@...nel.org
Cc: akpm@...ux-foundation.org,
	catalin.marinas@....com,
	changyuanl@...gle.com,
	graf@...zon.com,
	kexec@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	pasha.tatashin@...een.com,
	pratyush@...nel.org,
	ran.xiaokai@....com.cn,
	ranxiaokai627@....com
Subject: Re: [PATCH 2/2] liveupdate: Fix boot failure due to kmemleak access to unmapped pages

>On Thu, Nov 20, 2025 at 02:41:47PM +0000, ranxiaokai627@....com wrote:
>> Subject: liveupdate: Fix boot failure due to kmemleak access to unmapped pages
>
>Please prefix kexec handover patches with kho: rather than liveupdate.

Thanks for your review, i will update the patch subject.

>> 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 enabled, __free_pages() invokes
>> debug_pagealloc_unmap_pages(), clearing the _PAGE_PRESENT bit for
>> freed pages in the direct mapping.
>> Commit 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
>> releases the KHO scratch region via init_cma_reserved_pageblock(),
>> unmapping its physical pages. Subsequent kmemleak scanning accesses
>> these unmapped pages, triggering fatal page faults.
>> 
>> Call kmemleak_no_scan_phys() from kho_reserve_scratch() to
>> exclude the reserved region from scanning before
>> it is released to the buddy allocator.
>> 
>> Fixes: 3dc92c311498 ("kexec: add Kexec HandOver (KHO) generation helpers")
>> Signed-off-by: Ran Xiaokai <ran.xiaokai@....com.cn>
>> ---
>>  kernel/liveupdate/kexec_handover.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>> 
>> diff --git a/kernel/liveupdate/kexec_handover.c b/kernel/liveupdate/kexec_handover.c
>> index 224bdf5becb6..dd4942d1d76c 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>
>> @@ -654,6 +655,7 @@ static void __init kho_reserve_scratch(void)
>>  	if (!addr)
>>  		goto err_free_scratch_desc;
>>  
>> +	kmemleak_no_scan_phys(addr);
>
>There's kmemleak_ignore_phys() that can be called after the scratch areas
>allocated from memblock and with that kmemleak should not access them.
>
>Take a look at __cma_declare_contiguous_nid().

Thanks for catching this.
Since kmemleak_ignore_phys() perfectly handles this issue,
introducing another helper is unnecessary.
I'll post v2 shortly.

>>  	kho_scratch[i].addr = addr;
>>  	kho_scratch[i].size = size;
>>  	i++;
>
>-- 
>Sincerely yours,
>Mike.