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

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Message-ID: <aSBq8T8ETc3zjBf6@kernel.org>
Date: Fri, 21 Nov 2025 15:36:49 +0200
From: Mike Rapoport <rppt@...nel.org>
To: ranxiaokai627@....com
Cc: catalin.marinas@....com, akpm@...ux-foundation.org, graf@...zon.com,
	pasha.tatashin@...een.com, pratyush@...nel.org,
	changyuanl@...gle.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, kexec@...ts.infradead.org,
	ran.xiaokai@....com.cn
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.

> 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().

>  	kho_scratch[i].addr = addr;
>  	kho_scratch[i].size = size;
>  	i++;

-- 
Sincerely yours,
Mike.