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=1794590424; b=oxuOwgvUsC6vwXhnftcNc9LSG7zCipPYm/eSTnmRR10n4R4Zh6eyYPCawZFeoB26kV3c jNvdVcZnukcx9iR9e6brvPqCslslxIFylvif+MGbXsZdgAG/NVcat4o0ynDoxUPFa7gry dJQ8ArakqHnWq/B78nCgFeYUv41umnugvNu2jTkE4dP+Fo0lQokFgsl0/9DsCwUo3aSlK xmMh39gUSJ7bfkc+0Hj6KqF80E/+RbHCBODDdzpdWPxoI4aV1+Lnd8ByGEddDtHKnIeuE Zj3GW/Y1fsQ2/dKtSgkp+LWCbqvdb9cUU/aij3A0fci+PLLCaemPE/a/tFzEHieZpBQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794590424; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=YEo98+782kH7N6JW4ZjJ0dZ2pY9PMC/gxYi8l143zNM=; b=26UKmfOP5A6pi5qsTgSPRPfLz5scykOh5Nrx6VeSx4QF+xWGRoZOGEyoPURJ4+b5WyLg eQsGAPfuEewGLAMDjLhABRpa/GJ7n2RxtUkjwaC7KHN3uBCmMOVnqlK3ufBfmwz1WP6us 4EYNSEyxOe1RfLIGpD0k/05Znvla5+ca/t2Xr4lhHBj5EdMqvmS9pb7KBBE4iGmSyjwk4 V/590ijphcaOvWR80+2wFiZ2HONgBKbqDyQHneGF9wjHonffG4DVcIO4h1sXin5D8kphN VVkW2Lp4StLwzbdSYp5U5QP+D/X1CxUatau6CaW3+p+Ws7Gool/kmIuf848j170nCFQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=xR3s3wlC; 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 47FE6606E653; Fri, 13 Nov 2026 17:20:24 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=xR3s3wlC Received: by smtp.kernel.org (Postfix) with ESMTPSA id EC24E1F000C8; Fri, 13 Nov 2026 17:20:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794590424; bh=YEo98+782kH7N6JW4ZjJ0dZ2pY9PMC/gxYi8l143zNM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=xR3s3wlC07XqSptHKIoPvWQiAyTHuBdyQGor6YnolMSSJMcV4GoeaNRDtn4BK542F MzQodx1YBWAiKcx2pKW69BMJgfBNJJUtXfBis2HRGHtF6x/OiTeIacMlQSBE4g/vW7 uHeqGbDw4ilzJuAYYuQjhff/pKNKgZY6U3qCN5V4= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Chris Mason , "Lorenzo Stoakes (ARM)" , "Gregory Price (Meta)" , Muhammad Usama Anjum , Lance Yang , "David Hildenbrand (Arm)" , Sasha Levin Subject: [PATCH 6.18 387/686] mm/vma: call ->may_split() before a partial merge Date: Fri, 13 Nov 2026 10:48:40 -0500 Message-ID: <20261113153834.110294395@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261113153820.902362109@linuxfoundation.org> References: <20261113153820.902362109@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Chris Mason [ Upstream commit 0193e83368022a308d19ee0293f55a4f5d548e40 ] 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) Tested-by: Muhammad Usama Anjum Link: https://patch.msgid.link/20261031-fixes_core-v3-42-d6437171ecc3@kernel.org Reviewed-by: Lance Yang Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Sasha Levin --- mm/vma.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/mm/vma.c b/mm/vma.c index dadf7d69182c2..8669da66edc5c 100644 --- a/mm/vma.c +++ b/mm/vma.c @@ -485,6 +485,15 @@ void unmap_region(struct ma_state *mas, struct vm_area_struct *vma, 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. @@ -501,11 +510,9 @@ __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) @@ -875,6 +882,10 @@ 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. -- 2.53.0