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

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Message-ID: <mafs07bvbwipt.fsf@kernel.org>
Date: Thu, 27 Nov 2025 17:20:14 +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 v4] KHO: Fix boot failure due to kmemleak access to
 non-PRESENT pages

On Thu, Nov 27 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>

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

Thanks!

[...]

-- 
Regards,
Pratyush Yadav