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Date: Mon, 27 Oct 2025 15:33:23 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Kiryl Shutsemau <kirill@shutemov.name>
Cc: David Hildenbrand <david@redhat.com>, Hugh Dickins <hughd@google.com>,
 Matthew Wilcox <willy@infradead.org>, Alexander Viro
 <viro@zeniv.linux.org.uk>, Christian Brauner <brauner@kernel.org>, Lorenzo
 Stoakes <lorenzo.stoakes@oracle.com>, "Liam R. Howlett"
 <Liam.Howlett@oracle.com>, Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport
 <rppt@kernel.org>, Suren Baghdasaryan <surenb@google.com>, Michal Hocko
 <mhocko@suse.com>, Rik van Riel <riel@surriel.com>, Harry Yoo
 <harry.yoo@oracle.com>, Johannes Weiner <hannes@cmpxchg.org>, Shakeel Butt
 <shakeel.butt@linux.dev>, Baolin Wang <baolin.wang@linux.alibaba.com>,
 "Darrick J. Wong" <djwong@kernel.org>, Dave Chinner <david@fromorbit.com>,
 linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
 linux-kernel@vger.kernel.org, Kiryl Shutsemau <kas@kernel.org>
Subject: Re: [PATCHv3 1/2] mm/memory: Do not populate page table entries
 beyond i_size
Message-Id: <20251027153323.5eb2d97a791112f730e74a21@linux-foundation.org>
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On Mon, 27 Oct 2025 11:56:35 +0000 Kiryl Shutsemau <kirill@shutemov.name> wrote:

> From: Kiryl Shutsemau <kas@kernel.org>
> 
> Accesses within VMA, but beyond i_size rounded up to PAGE_SIZE are
> supposed to generate SIGBUS.
> 
> Recent changes attempted to fault in full folio where possible. They did
> not respect i_size, which led to populating PTEs beyond i_size and
> breaking SIGBUS semantics.
> 
> Darrick reported generic/749 breakage because of this.
> 
> However, the problem existed before the recent changes. With huge=always
> tmpfs, any write to a file leads to PMD-size allocation. Following the
> fault-in of the folio will install PMD mapping regardless of i_size.
> 
> Fix filemap_map_pages() and finish_fault() to not install:
>   - PTEs beyond i_size;
>   - PMD mappings across i_size;
> 
> Make an exception for shmem/tmpfs that for long time intentionally
> mapped with PMDs across i_size.
> 
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> Fixes: 19773df031bc ("mm/fault: try to map the entire file folio in finish_fault()")
> Fixes: 357b92761d94 ("mm/filemap: map entire large folio faultaround")
> Fixes: 01c70267053d ("fs: add a filesystem flag for THPs")

Multiple Fixes: are confusing.

We have two 6.18-rcX targets and one from 2020.  Are we asking people
to backport this all the way back to 2020?  If so I'd suggest the
removal of the more recent Fixes: targets.

Also, is [2/2] to be backported?  The changelog makes it sound that way,
but no Fixes: was identified?