linux-kernel - Re: [PATCH v4] mm/huge_memory: preserve PG_has_hwpoisoned if a folio is split to >0 order

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Message-ID: <b1d18017-548f-4219-8cba-351e7f8d29b9@linux.alibaba.com>
Date: Fri, 24 Oct 2025 10:08:31 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Zi Yan <ziy@...dia.com>, linmiaohe@...wei.com, david@...hat.com,
 jane.chu@...cle.com
Cc: kernel@...kajraghav.com, akpm@...ux-foundation.org, mcgrof@...nel.org,
 nao.horiguchi@...il.com, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 "Liam R. Howlett" <Liam.Howlett@...cle.com>, Nico Pache <npache@...hat.com>,
 Ryan Roberts <ryan.roberts@....com>, Dev Jain <dev.jain@....com>,
 Barry Song <baohua@...nel.org>, Lance Yang <lance.yang@...ux.dev>,
 "Matthew Wilcox (Oracle)" <willy@...radead.org>,
 Wei Yang <richard.weiyang@...il.com>, Yang Shi <shy828301@...il.com>,
 linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, stable@...r.kernel.org
Subject: Re: [PATCH v4] mm/huge_memory: preserve PG_has_hwpoisoned if a folio
 is split to >0 order

On 2025/10/23 11:05, Zi Yan wrote:
> folio split clears PG_has_hwpoisoned, but the flag should be preserved in
> after-split folios containing pages with PG_hwpoisoned flag if the folio is
> split to >0 order folios. Scan all pages in a to-be-split folio to
> determine which after-split folios need the flag.
> 
> An alternatives is to change PG_has_hwpoisoned to PG_maybe_hwpoisoned to
> avoid the scan and set it on all after-split folios, but resulting false
> positive has undesirable negative impact. To remove false positive, caller
> of folio_test_has_hwpoisoned() and folio_contain_hwpoisoned_page() needs to
> do the scan. That might be causing a hassle for current and future callers
> and more costly than doing the scan in the split code. More details are
> discussed in [1].
> 
> This issue can be exposed via:
> 1. splitting a has_hwpoisoned folio to >0 order from debugfs interface;
> 2. truncating part of a has_hwpoisoned folio in
>     truncate_inode_partial_folio().
> 
> And later accesses to a hwpoisoned page could be possible due to the
> missing has_hwpoisoned folio flag. This will lead to MCE errors.
> 
> Link: https://lore.kernel.org/all/CAHbLzkoOZm0PXxE9qwtF4gKR=cpRXrSrJ9V9Pm2DJexs985q4g@mail.gmail.com/ [1]
> Fixes: c010d47f107f ("mm: thp: split huge page to any lower order pages")
> Cc: stable@...r.kernel.org
> Signed-off-by: Zi Yan <ziy@...dia.com>
> ---

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>