From: Pedro Falcato <pfalcato@suse.de>
To: "Jérémy Jean" <Jeremy.Jean@oss.cyber.gouv.fr>
Cc: David Hildenbrand <david@kernel.org>, Zi Yan <ziy@nvidia.com>,
Baolin Wang <baolin.wang@linux.alibaba.com>,
"Liam R. Howlett" <liam@infradead.org>,
Nico Pache <nico.pache@linux.dev>,
Ryan Roberts <ryan.roberts@arm.com>, Dev Jain <dev.jain@arm.com>,
Barry Song <baohua@kernel.org>,
Lance Yang <lance.yang@linux.dev>,
Usama Arif <usama.arif@linux.dev>,
Kiryl Shutsemau <kas@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
stable@vger.kernel.org
Subject: Re: [PATCH] mm/khugepaged: reject shmem collapse ranges beyond i_size
Date: Thu, 12 Nov 2026 18:11:35 +0000 [thread overview]
Message-ID: <avYBFPhB46XWAG4A@pedro-suse.tail5790ac.ts.net> (raw)
In-Reply-To: <20261112142335.2749597-2-Jeremy.Jean@oss.cyber.gouv.fr>
On Thu, Nov 12, 2026 at 02:23:35PM +0000, Jérémy Jean wrote:
> MADV_COLLAPSE lets collapse_file() treat absent shmem pages as holes
> filled with zeros. It does not check i_size, which allows one present
> page to become a huge mapping that covers the whole collapse range,
> including pages beyond EOF. This makes those pages writable. A later
> file extension can expose their contents after F_SEAL_WRITE.
>
> Hold inode i_rwsem in read mode while collapsing shmem so i_size
> cannot change. Reject a collapse if its page range extends past
> i_size rounded up to PAGE_SIZE. Keep i_size_read() outside the
> page-cache XArray lock because its 32-bit SMP reader is not IRQ
> safe.
I don't think this is an issue. shmem/tmpfs purposefully maps with large pages
across i_size, and collapsing across i_size is a feature, not a bug.
--
Pedro
next prev parent reply other threads:[~2026-11-12 18:11 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-12 14:23 Jérémy Jean
2026-11-12 18:11 ` Pedro Falcato [this message]
2026-11-12 22:50 ` Andrew Morton
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