From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793306630; b=BhxP+NG5l/MckXtMFP5xcf6Aah+w3EtJ0AAR3DQy7IEY9tKP5TYbrj4I48Gzc5DV7uHY Tr4ADmxQJwNLt39wQ75d3+zxCNRMseFE8Q51ZRNzxA4CxC4Px9olhb9X1qqKP63yQVzLu JvZqQEZHVJfi7GCVLPeiENUx9wc/e+0mgsPCTlH/FuyuzW4ZtulMRm+e4QkEgyTFfaDqV hYPuJAnnKPUBEsnhBhDCQh8Dr9Y+BTCALLsRm6TiyhV3paScSNbGDF6+nE6/P8hK98ddW s/Tbs/ksUaK/U8KPOvVDeKm6YNnc36KDzdt9d5dh5Zbzssw/Px233/Bleow2Pztnq1g== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793306630; h=Received:DKIM-Signature:From:Date:Subject:MIME-Version:Content-Type: Content-Transfer-Encoding:Message-Id:References:In-Reply-To:To:Cc: X-Mailer:X-Developer-Signature:X-Developer-Key; bh=6IH8xaAe45mU8M57+EDLlFo4PLFfCZN3Im2S0WKlnK0=; b=Ps0aNRtiYhKuYuT/XFKEQrgTVI8xgX/flwJKH7dTrWIjPiX5eL92dMqxYSQvZazc4HjE nmgRTBEbm7mQG7g8zKgwQjgN7Pl8V2i6R9akyiUC9FPN54IiPA2tpf4tnmqQyCz4lKA9V n6Wh7eb86k+qWZ5OBjdZNGn9Tz2Hn8R/SQlvWZ113svmgVdXLeTsK19+0RyUtys7zGJgT 10h5haNFjABrHjMmxPZAzvPdIcoSNjAD3AWoC0aTJoguNPtVsle8t0Zj3NBS5p1FzJ59m JGrHorwvvwBkkKObo7ne3DHV8+eJszxovwi6VMpzzTQqGBKhi7I5m7bk4VRsW9yHdrw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b="FXCbw/KG"; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 0178E606A31D; Thu, 29 Oct 2026 20:43:49 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FXCbw/KG Received: by smtp.kernel.org (Postfix) with ESMTPSA id 09C171F031E0; Thu, 29 Oct 2026 20:43:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793306629; bh=6IH8xaAe45mU8M57+EDLlFo4PLFfCZN3Im2S0WKlnK0=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=FXCbw/KGkeADan6zqMALNi5auqZppW+OBphX7usMQRLTkZScs5lZeOWTnOPkT3HYE FzwNqfCPCPRcxwfG9bVzxOcBVT66ZZY64f9snScoYDQ+pTvG1hSXDrKXonFSpK1Kqd 6RBiwVQEpzPNpdM1PJYbB62704hVmMK6mNHCb/41sfYaaO5a0ObT75Zh0vxnKGmQS7 v34PbNeOF4vKtysFkjrqMd/EhUWkUkYBCwoHZTJXRjJ+RdzUVlIymGKA4ttHbOgOHE 3FcaANIDpL3t758KDwXRBEHA/EW2zThvb+Mb/YVaXxc5R5eN8n/MZoXYev776ycpcL EgPBtGftyGEaQ== From: "David Hildenbrand (Arm)" Date: Thu, 29 Oct 2026 21:33:37 +0100 Subject: [PATCH v2 42/47] mm/vma: call ->may_split() before a partial merge X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261029-fixes_core-v2-42-a64ce7f83abb@kernel.org> References: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> In-Reply-To: <20261029-fixes_core-v2-0-a64ce7f83abb@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org, "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=4060; i=david@kernel.org; h=from:subject:message-id; bh=oeEtIdns6TUl03fxOY3qVv1IgcZMbIMX+UxPpI52qI4=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLIer+3cf3Dnh6bQe9PUGDJndafMPDuR68SD7zccnhg2f z8UOCtYvaOUhUGMg0FWTJElKPi+wcuX62qr3fiYYeawMoEMYeDiFICJhNky/GbpEZrLHKi79fvz x1n2EQIuIksqPn7dYFvL/lRNPLc4PZKRYf2M6d3Gjv7FYV5/RXwcegTcRJ3l4veccNLkSGP7fF+ NBQA= X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A From: Chris Mason A driver can use the ->may_split() hook to forbid a VMA boundary at certain addresses. A device-dax device is a character device that gives raw access to a range of memory through mmap(). device-dax refuses any address that is not a multiple of the device's alignment through vm_ops->may_split. vma_merge_existing_range() can move boundaries, but does not call vm_ops->may_split. If a range at the edge of a VMA gets the attributes of the adjacent VMA, the function moves only that range over to the neighbour: one VMA shrinks and the other grows. This is a partial merge, and vma_modify() tries it before any split. Take a device-dax VMA that lies next to another VMA of the same file. The user calls mprotect() on the one page of the first VMA that touches the second VMA, and asks for the protection that the second VMA already has. The result is a partial merge. It puts the boundary inside a 1 GiB mapping, which is a single leaf entry at the PUD level. As part of the merge, the kernel looks for a huge PMD to split at the new boundary. That code does not expect a PUD leaf: vma_merge_existing_range() commit_merge() vma_adjust_trans_huge() split_huge_pmd_address() mm_find_pmd() treats the PUD leaf as a pointer to a PMD table, so the "table" is the device memory that the leaf maps __split_huge_pmd() reads a PMD that the user wrote to the device memory folio_put() on the folio that this PMD names Bad. While the code must at some point be taught to split PUD entries as well, the issue here is that we move VMA boundaries such that they are incompatible with the driver. Fix this by calling ->may_split() on the address that a partial merge would move the boundary to, and by abandoning the merge if the driver refuses. vma_modify() then tries the split, which fails with -EINVAL. Factor out existing split handling into check_split() and reuse it. Fix generated by an LLM and sent by Chris Mason in private. Fixes: 38607c62b34b ("fs/dax: properly refcount fs dax pages") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason Reviewed-by: Lorenzo Stoakes (ARM) [ david: improve description; cleanup the code ] Reviewed-by: Gregory Price (Meta) Tested-by: Gregory Price (Meta) Signed-off-by: Gregory Price (Meta) Signed-off-by: David Hildenbrand (Arm) --- mm/vma.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/mm/vma.c b/mm/vma.c index 1be613044b4a..acdf00346cda 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -516,6 +516,15 @@ void unmap_region(struct unmap_desc *unmap) tlb_finish_mmu(&tlb); } +static int check_split(struct vm_area_struct *vma, unsigned long addr) +{ + if (!vma->vm_ops) + return 0; + if (!vma->vm_ops->may_split) + return 0; + return vma->vm_ops->may_split(vma, addr); +} + /* * __split_vma() bypasses sysctl_max_map_count checking. We use this where it * has already been checked or doesn't make sense to fail. @@ -532,11 +541,9 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, WARN_ON(vma->vm_start >= addr); WARN_ON(vma->vm_end <= addr); - if (vma->vm_ops && vma->vm_ops->may_split) { - err = vma->vm_ops->may_split(vma, addr); - if (err) - return err; - } + err = check_split(vma, addr); + if (err) + return err; new = vm_area_dup(vma); if (!new) @@ -948,6 +955,10 @@ static __must_check struct vm_area_struct *vma_merge_existing_range( if (vmg->__remove_middle && !can_merge_remove_vma(middle)) return NULL; + /* If middle isn't removed then it's resized, i.e. splits. */ + if (!vmg->__remove_middle && check_split(middle, left_side ? end : start)) + return NULL; + /* * If we merge both VMAs, then next is also deleted. This implies * merge_will_delete_vma also. -- 2.43.0