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Date: Wed, 2 Sep 2026 19:34:38 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Kaitao Cheng <kaitao.cheng@linux.dev>
Cc: David Hildenbrand <david@kernel.org>, Zi Yan <ziy@nvidia.com>, Matthew
 Brost <matthew.brost@intel.com>, Joshua Hahn <joshua.hahnjy@gmail.com>,
 Rakie Kim <rakie.kim@sk.com>, Byungchul Park <byungchul@sk.com>, Gregory
 Price <gourry@gourry.net>, Ying Huang <ying.huang@linux.alibaba.com>,
 Alistair Popple <apopple@nvidia.com>, Naoya Horiguchi
 <nao.horiguchi@gmail.com>, Mel Gorman <mel@csn.ul.ie>, Andi Kleen
 <ak@linux.intel.com>, Muchun Song <muchun.song@linux.dev>, Jun'ichi Nomura
 <j-nomura@ce.jp.nec.com>, linux-mm@kvack.org, linux-kernel@vger.kernel.org,
 Kaitao Cheng <chengkaitao@kylinos.cn>
Subject: Re: [PATCH] migrate: Skip hwpoisoned hugetlb folios during
 migration
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On Wed,  1 Jul 2026 18:55:44 +0800 Kaitao Cheng <kaitao.cheng@linux.dev> wrote:

> Date: Wed,  1 Jul 2026 18:55:44 +0800

Well.

> Hugetlb migration does not check whether the source folio contains
> hwpoisoned memory before trying to move it.  After the folio is unmapped,
> the move path can reach hugetlbfs_migrate_folio() and then
> migrate_huge_page_move_mapping(), which copies the source folio into the
> new folio.
> 
> That copy uses folio_mc_copy(), so architectures with recoverable
> machine-check copy support can fail the copy with -EHWPOISON.  However,
> there is no reason to attempt the move once the source folio is already
> known to contain poisoned memory.  Architectures without such copy_mc
> support also fall back to a normal copy, which can consume the poison.
> 
> Check folio_contain_hwpoisoned_page() after locking the source hugetlb
> folio and fail the migration with -EHWPOISON before unmapping or copying
> it.  This covers both a hwpoisoned hugetlb head folio and large folios
> that only have the has_hwpoisoned summary flag set.

As always: please provide a description of the userspace-visible
runtime effects of the bug.

Even better if you can present a reproducer.

> Fixes: 290408d4a250 ("hugetlb: hugepage migration core")

Oct, 2010.  So I'm assuming this isn't super-urgent.

otoh, now it's out there and known about, perhaps Bad Guys can find a
way of triggering this, so the urgency becomes higher.


Anyway, please consider the Sashiko report
(https://sashiko.dev/#/patchset/20260701105544.97059-1-kaitao.cheng@linux.dev)
then update the changelog with the above info.  Decide whether we
should cc:stable (and describe why) then resend?

Thanks.