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 8A52919ADBA for ; Thu, 20 Nov 2025 15:56:28 +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=1763654188; cv=none; b=ItxZ5Ojz27tfnE0hMVPj8MHeoTUuhgRMdnaQd4yw4cSUWhJ1OxeXnAzmTCdISP3kHSe9d7A1a3hcN2WGZyGoqbLzJAGBqJHM8z+dqeA0fc1jyChZGsteZROQXIgnQiZH4ZSw1+5HQpyR0w6aMIH8ckUp1OH+GX3bMXyOoNNQjxg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763654188; c=relaxed/simple; bh=YkN1ug8kY+zNCgPmMPSf3gWwjII6q2tNgeLRiqsOQ3M=; h=Subject:To:Cc:From:Date:Message-ID:MIME-Version:Content-Type; b=f0PPJ2I5ov9wwxxkvgBmiI1n8tv3Dq4XBE15spl3QGxZk0WJbuZucSZB+hCeUW812Mj1zBrNPQgRJ3ezFDvIkjRRTzQj5DC7aY2wl5aR4BTntmMXOCvw9s6i2EWdAZWGFJVKWiqfIoe12NXclZuxo5U7VhLToquKKprt6n0unzQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=Sjzuwjv1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="Sjzuwjv1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9F174C116C6; Thu, 20 Nov 2025 15:56:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1763654188; bh=YkN1ug8kY+zNCgPmMPSf3gWwjII6q2tNgeLRiqsOQ3M=; h=Subject:To:Cc:From:Date:From; b=Sjzuwjv1CxF/xEuRcPgNXnXZqZdhiVLamVAc+fA+g06gfHDtoOOKLAsP7yEvqODv4 IpI9wj6DNIaU00LNO9FZeDfYJeG3dSQPOsPhcwm5elkoWDPXkJNgNX8pCp6x3wZ5BC 1K0+7Zk52cvfwEfdTidUz84m0yz1Mm4mDUD883PU= Subject: FAILED: patch "[PATCH] mm/memory: do not populate page table entries beyond i_size" failed to apply to 6.17-stable tree To: kas@kernel.org,akpm@linux-foundation.org,baolin.wang@linux.alibaba.com,brauner@kernel.org,david@fromorbit.com,david@redhat.com,djwong@kernel.org,hannes@cmpxchg.org,hughd@google.com,liam.howlett@oracle.com,lorenzo.stoakes@oracle.com,mhocko@suse.com,riel@surriel.com,rppt@kernel.org,shakeel.butt@linux.dev,stable@vger.kernel.org,surenb@google.com,vbabka@suse.cz,viro@zeniv.linux.org.uk,willy@infradead.org Cc: From: Date: Thu, 20 Nov 2025 16:56:22 +0100 Message-ID: <2025112022-pretender-version-d5b3@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.17-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.17.y git checkout FETCH_HEAD git cherry-pick -x 74207de2ba10c2973334906822dc94d2e859ffc5 # git commit -s git send-email --to '' --in-reply-to '2025112022-pretender-version-d5b3@gregkh' --subject-prefix 'PATCH 6.17.y' HEAD^.. Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 74207de2ba10c2973334906822dc94d2e859ffc5 Mon Sep 17 00:00:00 2001 From: Kiryl Shutsemau Date: Mon, 27 Oct 2025 11:56:35 +0000 Subject: [PATCH] mm/memory: do not populate page table entries beyond i_size Patch series "Fix SIGBUS semantics with large folios", v3. Accessing memory within a VMA, but beyond i_size rounded up to the next page size, is supposed to generate SIGBUS. Darrick reported[1] an xfstests regression in v6.18-rc1. generic/749 failed due to missing SIGBUS. This was caused by my recent changes that try to fault in the whole folio where possible: 19773df031bc ("mm/fault: try to map the entire file folio in finish_fault()") 357b92761d94 ("mm/filemap: map entire large folio faultaround") These changes did not consider i_size when setting up PTEs, leading to xfstest breakage. However, the problem has been present in the kernel for a long time - since huge tmpfs was introduced in 2016. The kernel happily maps PMD-sized folios as PMD without checking i_size. And huge=always tmpfs allocates PMD-size folios on any writes. I considered this corner case when I implemented a large tmpfs, and my conclusion was that no one in their right mind should rely on receiving a SIGBUS signal when accessing beyond i_size. I cannot imagine how it could be useful for the workload. But apparently filesystem folks care a lot about preserving strict SIGBUS semantics. Generic/749 was introduced last year with reference to POSIX, but no real workloads were mentioned. It also acknowledged the tmpfs deviation from the test case. POSIX indeed says[3]: References within the address range starting at pa and continuing for len bytes to whole pages following the end of an object shall result in delivery of a SIGBUS signal. The patchset fixes the regression introduced by recent changes as well as more subtle SIGBUS breakage due to split failure on truncation. This patch (of 2): 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. Link: https://lkml.kernel.org/r/20251027115636.82382-1-kirill@shutemov.name Link: https://lkml.kernel.org/r/20251027115636.82382-2-kirill@shutemov.name Signed-off-by: Kiryl Shutsemau Fixes: 6795801366da ("xfs: Support large folios") Reported-by: "Darrick J. Wong" Cc: Al Viro Cc: Baolin Wang Cc: Christian Brauner 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 diff --git a/mm/filemap.c b/mm/filemap.c index 13f0259d993c..2f1e7e283a51 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3681,7 +3681,8 @@ static struct folio *next_uptodate_folio(struct xa_state *xas, static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf, struct folio *folio, unsigned long start, unsigned long addr, unsigned int nr_pages, - unsigned long *rss, unsigned short *mmap_miss) + unsigned long *rss, unsigned short *mmap_miss, + bool can_map_large) { unsigned int ref_from_caller = 1; vm_fault_t ret = 0; @@ -3696,7 +3697,7 @@ static vm_fault_t filemap_map_folio_range(struct vm_fault *vmf, * The folio must not cross VMA or page table boundary. */ addr0 = addr - start * PAGE_SIZE; - if (folio_within_vma(folio, vmf->vma) && + if (can_map_large && folio_within_vma(folio, vmf->vma) && (addr0 & PMD_MASK) == ((addr0 + folio_size(folio) - 1) & PMD_MASK)) { vmf->pte -= start; page -= start; @@ -3811,13 +3812,27 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, unsigned long rss = 0; unsigned int nr_pages = 0, folio_type; unsigned short mmap_miss = 0, mmap_miss_saved; + bool can_map_large; rcu_read_lock(); folio = next_uptodate_folio(&xas, mapping, end_pgoff); if (!folio) goto out; - if (filemap_map_pmd(vmf, folio, start_pgoff)) { + file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; + end_pgoff = min(end_pgoff, file_end); + + /* + * Do not allow to map with PTEs beyond i_size and with PMD + * across i_size to preserve SIGBUS semantics. + * + * Make an exception for shmem/tmpfs that for long time + * intentionally mapped with PMDs across i_size. + */ + can_map_large = shmem_mapping(mapping) || + file_end >= folio_next_index(folio); + + if (can_map_large && filemap_map_pmd(vmf, folio, start_pgoff)) { ret = VM_FAULT_NOPAGE; goto out; } @@ -3830,10 +3845,6 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, goto out; } - file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE) - 1; - if (end_pgoff > file_end) - end_pgoff = file_end; - folio_type = mm_counter_file(folio); do { unsigned long end; @@ -3850,7 +3861,8 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, else ret |= filemap_map_folio_range(vmf, folio, xas.xa_index - folio->index, addr, - nr_pages, &rss, &mmap_miss); + nr_pages, &rss, &mmap_miss, + can_map_large); folio_unlock(folio); } while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL); diff --git a/mm/memory.c b/mm/memory.c index 74b45e258323..b59ae7ce42eb 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -65,6 +65,7 @@ #include #include #include +#include #include #include #include @@ -5501,8 +5502,25 @@ vm_fault_t finish_fault(struct vm_fault *vmf) return ret; } + if (!needs_fallback && vma->vm_file) { + struct address_space *mapping = vma->vm_file->f_mapping; + pgoff_t file_end; + + file_end = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE); + + /* + * Do not allow to map with PTEs beyond i_size and with PMD + * across i_size to preserve SIGBUS semantics. + * + * Make an exception for shmem/tmpfs that for long time + * intentionally mapped with PMDs across i_size. + */ + needs_fallback = !shmem_mapping(mapping) && + file_end < folio_next_index(folio); + } + if (pmd_none(*vmf->pmd)) { - if (folio_test_pmd_mappable(folio)) { + if (!needs_fallback && folio_test_pmd_mappable(folio)) { ret = do_set_pmd(vmf, folio, page); if (ret != VM_FAULT_FALLBACK) return ret;