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: <479c9b79-a8a3-6e14-9264-cda3e9851b43@huawei.com>
Date: Fri, 24 Oct 2025 15:44:07 +0800
From: Miaohe Lin <linmiaohe@...wei.com>
To: Zi Yan <ziy@...dia.com>
CC: <kernel@...kajraghav.com>, <akpm@...ux-foundation.org>,
	<mcgrof@...nel.org>, <nao.horiguchi@...il.com>, Lorenzo Stoakes
	<lorenzo.stoakes@...cle.com>, Baolin Wang <baolin.wang@...ux.alibaba.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>, <david@...hat.com>, <jane.chu@...cle.com>
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>

Thanks for your patch. LGTM.

Reviewed-by: Miaohe Lin <linmiaohe@...wei.com>

Thanks.
.