From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5A9241FF1C4; Mon, 10 Nov 2025 05:20:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762752026; cv=none; b=WuJK/lGLGPKTan0STPzgLlEHXi8eV2JzecmqKXImc1IUtQKfUT/xRfEAPBRDbMGwE5gLX3yPyJRPNg/7iWmg0Xj71jiJz0tL7kalmCfiosQDR5yTZAGz4fLn7zF2jBW2drXy1MOUjAygrO2G6vP2yVBW0ROvi5I8dyYgHrIdF+0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1762752026; c=relaxed/simple; bh=bBOkItYCk+2YK5Jd2K/iSqJMHSdCIqlCKjghffTHXdA=; h=Date:To:From:Subject:Message-Id; b=SSBER/pybl5kkfNoqQqP9gtkRbQ8eU7RqHF0F43gtNUel8+//9QaxhBAJE7bTVmmgQXQ88lkbewLKVamDE1Hsg1ySOF4cj88v19+VwoEig8lPfhXiFQY8wuCjk75uixKZDlAsY/D/+H+fWmdBljHnx6J26HB5kkBu5FsR68D3rQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=YaQl+PUn; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="YaQl+PUn" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CFC52C4CEFB; Mon, 10 Nov 2025 05:20:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1762752025; bh=bBOkItYCk+2YK5Jd2K/iSqJMHSdCIqlCKjghffTHXdA=; h=Date:To:From:Subject:From; b=YaQl+PUnGYitO3WT+mifgdnRyS4XaCNXFYst/3CJqm1jn+FfwgVUhL5k11GK31QUN uyQRTORosXlk8lq988HNVdNg5DHc32OP9RruN/QgLOuy5JnjcprJRT1XK4KmVM7iyp odH0U3TcolU0kLYWMfrDBHGBJ+MzuMku6ghJRQLA= Date: Sun, 09 Nov 2025 21:20:25 -0800 To: mm-commits@vger.kernel.org,willy@infradead.org,viro@zeniv.linux.org.uk,vbabka@suse.cz,surenb@google.com,stable@vger.kernel.org,shakeel.butt@linux.dev,rppt@kernel.org,riel@surriel.com,mhocko@suse.com,lorenzo.stoakes@oracle.com,liam.howlett@oracle.com,hughd@google.com,hannes@cmpxchg.org,djwong@kernel.org,david@redhat.com,david@fromorbit.com,brauner@kernel.org,baolin.wang@linux.alibaba.com,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] mm-truncate-unmap-large-folio-on-split-failure.patch removed from -mm tree Message-Id: <20251110052025.CFC52C4CEFB@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The quilt patch titled Subject: mm/truncate: unmap large folio on split failure has been removed from the -mm tree. Its filename was mm-truncate-unmap-large-folio-on-split-failure.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Kiryl Shutsemau Subject: mm/truncate: unmap large folio on split failure Date: Mon, 27 Oct 2025 11:56:36 +0000 Accesses within VMA, but beyond i_size rounded up to PAGE_SIZE are supposed to generate SIGBUS. This behavior might not be respected on truncation. During truncation, the kernel splits a large folio in order to reclaim memory. As a side effect, it unmaps the folio and destroys PMD mappings of the folio. The folio will be refaulted as PTEs and SIGBUS semantics are preserved. However, if the split fails, PMD mappings are preserved and the user will not receive SIGBUS on any accesses within the PMD. Unmap the folio on split failure. It will lead to refault as PTEs and preserve SIGBUS semantics. Make an exception for shmem/tmpfs that for long time intentionally mapped with PMDs across i_size. Link: https://lkml.kernel.org/r/20251027115636.82382-3-kirill@shutemov.name Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios") Signed-off-by: Kiryl Shutsemau Cc: Al Viro Cc: Baolin Wang Cc: Christian Brauner Cc: "Darrick J. Wong" Cc: Dave Chinner Cc: David Hildenbrand Cc: Hugh Dickins Cc: Johannes Weiner Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Matthew Wilcox (Oracle) Cc: Michal Hocko Cc: Mike Rapoport Cc: Rik van Riel Cc: Shakeel Butt Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton --- mm/truncate.c | 35 +++++++++++++++++++++++++++++------ 1 file changed, 29 insertions(+), 6 deletions(-) --- a/mm/truncate.c~mm-truncate-unmap-large-folio-on-split-failure +++ a/mm/truncate.c @@ -177,6 +177,32 @@ int truncate_inode_folio(struct address_ return 0; } +static int try_folio_split_or_unmap(struct folio *folio, struct page *split_at, + unsigned long min_order) +{ + enum ttu_flags ttu_flags = + TTU_SYNC | + TTU_SPLIT_HUGE_PMD | + TTU_IGNORE_MLOCK; + int ret; + + ret = try_folio_split_to_order(folio, split_at, min_order); + + /* + * If the split fails, unmap the folio, so it will be refaulted + * with PTEs to respect SIGBUS semantics. + * + * Make an exception for shmem/tmpfs that for long time + * intentionally mapped with PMDs across i_size. + */ + if (ret && !shmem_mapping(folio->mapping)) { + try_to_unmap(folio, ttu_flags); + WARN_ON(folio_mapped(folio)); + } + + return ret; +} + /* * Handle partial folios. The folio may be entirely within the * range if a split has raced with us. If not, we zero the part of the @@ -226,7 +252,7 @@ bool truncate_inode_partial_folio(struct min_order = mapping_min_folio_order(folio->mapping); split_at = folio_page(folio, PAGE_ALIGN_DOWN(offset) / PAGE_SIZE); - if (!try_folio_split_to_order(folio, split_at, min_order)) { + if (!try_folio_split_or_unmap(folio, split_at, min_order)) { /* * try to split at offset + length to make sure folios within * the range can be dropped, especially to avoid memory waste @@ -250,13 +276,10 @@ bool truncate_inode_partial_folio(struct if (!folio_trylock(folio2)) goto out; - /* - * make sure folio2 is large and does not change its mapping. - * Its split result does not matter here. - */ + /* make sure folio2 is large and does not change its mapping */ if (folio_test_large(folio2) && folio2->mapping == folio->mapping) - try_folio_split_to_order(folio2, split_at2, min_order); + try_folio_split_or_unmap(folio2, split_at2, min_order); folio_unlock(folio2); out: _ Patches currently in -mm which might be from kas@kernel.org are