From: Lance Yang <lance.yang@linux.dev>
To: Usama Arif <usama.arif@linux.dev>
Cc: aarcange@redhat.com, ziy@nvidia.com, david@kernel.org,
baolin.wang@linux.alibaba.com, baohua@kernel.org,
ryan.roberts@arm.com, npache@redhat.com, ljs@kernel.org,
dev.jain@arm.com, linux-mm@kvack.org,
sashiko-bot <sashiko-bot@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org, kernel-team@meta.com,
hannes@cmpxchg.org, shakeel.butt@linux.dev, riel@surriel.com,
liam@infradead.org
Subject: Re: [PATCH] userfaultfd: wait on source PMD during UFFDIO_MOVE
Date: Mon, 6 Jul 2026 10:18:00 +0800 [thread overview]
Message-ID: <eeb3e66a-c140-4347-b86f-c47da2cd9886@linux.dev> (raw)
In-Reply-To: <20260705131231.1499198-1-usama.arif@linux.dev>
On 2026/7/5 21:12, Usama Arif wrote:
> move_pages_huge_pmd() snapshots src_pmdval under src_ptl, drops the lock,
> and, for migration entries, waits with pmd_migration_entry_wait().
>
> Passing &src_pmdval is wrong. pmd_migration_entry_wait() must lock and
> re-read the real page-table PMD; on split-PMD-lock kernels, a stack
> address also resolves to the wrong lock. softleaf_entry_wait_on_locked()
Well spotted!
> then waits without a folio reference, which is safe only while serialized
> against migration-entry removal by the real PT lock.
>
> Pass src_pmd, matching __handle_mm_fault() and hmm_vma_walk_pmd().
>
> Reported-by: sashiko-bot <sashiko-bot@kernel.org>
> Link: https://sashiko.dev/#/patchset/20260703173903.3789516-1-usama.arif%40linux.dev?part=8
> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
> Signed-off-by: Usama Arif <usama.arif@linux.dev>
> ---
As Andrew and Baolin pointed out, this should go to stable ;)
With that,
Reviewed-by: Lance Yang <lance.yang@linux.dev>
next prev parent reply other threads:[~2026-07-06 2:18 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-07-05 13:12 [PATCH] userfaultfd: wait on source PMD during UFFDIO_MOVE Usama Arif
2026-07-05 19:08 ` Rik van Riel
2026-07-05 19:24 ` Andrew Morton
2026-07-06 1:05 ` Baolin Wang
2026-07-06 2:18 ` Lance Yang [this message]
2026-07-06 9:00 ` David Hildenbrand (Arm)
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