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 374AE3242C7 for ; Thu, 20 Nov 2025 18:17:08 +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=1763662630; cv=none; b=HaR9d5ksCe3bpsXfKfFbnEyOaqalp2Y0QOEO4bISmehZVcYEfP93TN/ecqCiEgDj96imVQNiVkp/OKoQsmoBkNZl/PGXXdEfJ5Oou9k2WN7Bziavnbwr8NEgyhC9CO5tWu+xIQq5Fl1DrfSluiESxi3z5t+xx7/aL6R7CGragXw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1763662630; c=relaxed/simple; bh=QWVeMh8fMWeJvtk9LMQumbs4SADPpV6Vb4blT/fwgjQ=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GR+qSHhTXqZwnvI56rRjDmk6FBxAgFjoGuBUGsIkI3o2ln4fiqKvWKaEFdCGO/atKG11SpxWyjNHp1p4r1Wf4oiy3um73XmBOTfY49NO/WmVNypH2/vVUKso3Y3pJ3m3dn8zcKn4zC3XWxmI6uFuSwvwbqHR7zyJ+qz2CrnmN+s= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=fxVxvapg; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="fxVxvapg" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 48BCBC4AF0B; Thu, 20 Nov 2025 18:17:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1763662628; bh=QWVeMh8fMWeJvtk9LMQumbs4SADPpV6Vb4blT/fwgjQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=fxVxvapg4kZk+PO+i8BGONwZ6KurIbtKSY/K0S9IvnuJ1zdwh1bbimBjYrFO1Gjx0 72n+k0LEnY60jCBSXuHiUoJIFU85RZCIIntbN/GqjwU3zbz37rdVaeJGz0ZhSLsvGA Zdq47P7UiAMOCESFz/Djqvp7u8/7EHQWLVQF0z9oXmDlnxStO2ghI1LIHwNIQvE7K5 Gi+qNEfoO6Nd0cxO/EbSwtkgAYthqaIDviGyqDEkT+VreZYOZWiFLnTOgRArW4QDt3 FDOgr6c6vmJKxWyNf/o2sTmrlgpTJXDZP8CksAwHLs8l0yrZcMal/kMLwzXtU/JhQ2 PJOfOcBLFhwZA== Received: from phl-compute-02.internal (phl-compute-02.internal [10.202.2.42]) by mailfauth.phl.internal (Postfix) with ESMTP id 9763EF40070; Thu, 20 Nov 2025 13:17:07 -0500 (EST) Received: from phl-mailfrontend-01 ([10.202.2.162]) by phl-compute-02.internal (MEProxy); Thu, 20 Nov 2025 13:17:07 -0500 X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeeffedrtdeggddvvdejjeekucetufdoteggodetrf dotffvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfurfetoffkrfgpnffqhgenuceu rghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmnecujf gurhephffvvefufffkofgjfhgggfestdekredtredttdenucfhrhhomhepmfhirhihlhcu ufhhuhhtshgvmhgruhcuoehkrghssehkvghrnhgvlhdrohhrgheqnecuggftrfgrthhtvg hrnhepgeejffehvdeltdefteejieehveeuffeuteevhfehvdejieelteffleefleeiffeh necuffhomhgrihhnpehkvghrnhgvlhdrohhrghenucevlhhushhtvghrufhiiigvpedtne curfgrrhgrmhepmhgrihhlfhhrohhmpehkihhrihhllhdomhgvshhmthhprghuthhhphgv rhhsohhnrghlihhthidqudeiudduiedvieehhedqvdekgeeggeejvdekqdhkrghspeepkh gvrhhnvghlrdhorhhgsehshhhuthgvmhhovhdrnhgrmhgvpdhnsggprhgtphhtthhopedv tddpmhhouggvpehsmhhtphhouhhtpdhrtghpthhtohepshhtrggslhgvsehvghgvrhdrkh gvrhhnvghlrdhorhhgpdhrtghpthhtohepkhgrsheskhgvrhhnvghlrdhorhhgpdhrtghp thhtohepughjfihonhhgsehkvghrnhgvlhdrohhrghdprhgtphhtthhopehvihhrohesii gvnhhivhdrlhhinhhugidrohhrghdruhhkpdhrtghpthhtohepsggrohhlihhnrdifrghn gheslhhinhhugidrrghlihgsrggsrgdrtghomhdprhgtphhtthhopegsrhgruhhnvghrse hkvghrnhgvlhdrohhrghdprhgtphhtthhopegurghvihgusehfrhhomhhorhgsihhtrdgt ohhmpdhrtghpthhtohepuggrvhhiugesrhgvughhrghtrdgtohhmpdhrtghpthhtohephh hughhhugesghhoohhglhgvrdgtohhm X-ME-Proxy: Feedback-ID: i10464835:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 20 Nov 2025 13:17:07 -0500 (EST) From: Kiryl Shutsemau To: stable@vger.kernel.org Cc: Kiryl Shutsemau , "Darrick J. Wong" , Al Viro , Baolin Wang , Christian Brauner , Dave Chinner , David Hildenbrand , Hugh Dickins , Johannes Weiner , Liam Howlett , Lorenzo Stoakes , "Matthew Wilcox (Oracle)" , Michal Hocko , Mike Rapoport , Rik van Riel , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka , Andrew Morton Subject: [PATCH 6.6.y 2/2] mm/memory: do not populate page table entries beyond i_size Date: Thu, 20 Nov 2025 18:16:57 +0000 Message-ID: <20251120181657.964919-2-kas@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251120181657.964919-1-kas@kernel.org> References: <2025112025-voucher-hexagram-61bf@gregkh> <20251120181657.964919-1-kas@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 (cherry picked from commit 74207de2ba10c2973334906822dc94d2e859ffc5) Signed-off-by: Kiryl Shutsemau --- mm/filemap.c | 20 +++++++++++++++----- mm/memory.c | 24 +++++++++++++++++++++++- 2 files changed, 38 insertions(+), 6 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index 7d4d3bea4e1e..6e01364a1ca6 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3614,13 +3614,27 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, struct folio *folio; vm_fault_t ret = 0; unsigned int nr_pages = 0, 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; } @@ -3633,10 +3647,6 @@ 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; - do { unsigned long end; diff --git a/mm/memory.c b/mm/memory.c index 8b80db7115e5..fd917a5bc961 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -67,6 +67,7 @@ #include #include #include +#include #include #include #include @@ -4435,6 +4436,8 @@ static bool vmf_pte_changed(struct vm_fault *vmf) vm_fault_t finish_fault(struct vm_fault *vmf) { struct vm_area_struct *vma = vmf->vma; + bool needs_fallback = false; + struct folio *folio; struct page *page; vm_fault_t ret; @@ -4444,6 +4447,8 @@ vm_fault_t finish_fault(struct vm_fault *vmf) else page = vmf->page; + folio = page_folio(page); + /* * check even for read faults because we might have lost our CoWed * page @@ -4454,8 +4459,25 @@ 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 (PageTransCompound(page)) { + if (!needs_fallback && PageTransCompound(page)) { ret = do_set_pmd(vmf, page); if (ret != VM_FAULT_FALLBACK) return ret; -- 2.51.0