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

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Message-ID: <mafs0see3zkug.fsf@kernel.org>
Date: Mon, 24 Nov 2025 13:16:55 +0100
From: Pratyush Yadav <pratyush@...nel.org>
To: ranxiaokai627@....com
Cc: rppt@...nel.org,  akpm@...ux-foundation.org,  catalin.marinas@....com,
  changyuanl@...gle.com,  graf@...zon.com,  pasha.tatashin@...een.com,
  pratyush@...nel.org,  kexec@...ts.infradead.org,
  linux-kernel@...r.kernel.org,  linux-mm@...ck.org,
  ran.xiaokai@....com.cn
Subject: Re: [PATCH v3] KHO: Fix boot failure due to kmemleak access to
 non-PRESENT pages

On Mon, Nov 24 2025, ranxiaokai627@....com wrote:

> 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.
> 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@....com.cn>
> Reviewed-by: Mike Rapoport (Microsoft) <rppt@...nel.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?

After that,

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

[0] https://lore.kernel.org/all/20251122175735.92578-1-ranxiaokai627@163.com/

>  		for (pfn = base_pfn; pfn < base_pfn + count;
>  		     pfn += pageblock_nr_pages)
>  			init_cma_reserved_pageblock(pfn_to_page(pfn));

-- 
Regards,
Pratyush Yadav