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=1794045933; b=ql6g+vlVRMuZ55zWuh5Fu8ohJ5kK3YmSZnnLTRPlXbSyyxBBEVz0vH0Vq/HPqolfZnZC kCEzNTLvXgLuw2WzAh3SBs5/OSp4/+SLZPVNiyRcj78atN2QTz8b3VosnOw7FNoGQWzyX tlRapN0gCAmii3D1GbtghypiBmx3vXzX4XIx1RDOzx0YV+TI2G16v3Kr0/wvkBkv+vzMK +4/s9otv0FQXmcbSYzmsFQs9dWExeq+JBAoJjCCKm3r25miGQ+5fiS8gjd9JrniVEmIqW cCTPkoa9XuFX8Nk6YoWry/KGcQ+NYriZvVazFRSpOZALPqFqrJFYhnfsLUfIehXw+Ng== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794045933; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=T5Jkr4UtJyeAEXfPXYg5udwVQFW6Vr4nJKy/I9Intek=; b=U7pD9HnIILdAz/JOUPGkDSRb9gDHX4lyYimLD8P0GPGdu25paBK/icMbt6ItJuvjZNlb qDqI6SMTxoSj5OtwrAi+4KIL9XNg481KsnScV80UbxuJdvusYcMtYujFX628OK/W/lqPo F5kmTNnh3zhXYpBVygUKRhqWE3omuOs+ybdvO2eePnnqiY0yGWnkTOu79FS4kaKmU03hs 0dBtBfu69RZTUVVKMcklI4potdoP2wlMGBYsGZjFLFE7N1nr3DsvfdPtrzairMEIjAu2S 3IWxn2OW20AqVsyB3unka9c6wLcnxrhs+4tjI8IcIlB7/b3NzNKcj3SGeS5LWouEzwA== 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=hu61Lxj1; 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 936C1606A326 for ; Sat, 7 Nov 2026 10:05:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=hu61Lxj1 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2B6601F0089F; Sat, 7 Nov 2026 10:05:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794045933; bh=T5Jkr4UtJyeAEXfPXYg5udwVQFW6Vr4nJKy/I9Intek=; h=From:To:Cc:Subject:Date; b=hu61Lxj1gLrEY8GuE0jX9HCLAY86hz5imTMFpoZvkCUBymvZnsasNGW1EFZBqySBL xYBlzP5GXyGDgAzjvtGYOZguAELJrYhU369ISHe52pjw5kBuo84ZFFDrrQy3gAlHfF LQkJBH0+C2TtRpCLjTCiJV3/l4PhStsUwtJqfLBqaEfMckMOjlevsFA5cV3f35ezsM lXGIXSafbIpvYjDifz7zw4oFSv5pAqn3IoEuJgOIIqIQ/mvUQjA+vvRQckiSfNpJiD 1VAf9S7mCnSpwFNV+N7lkEvdFskO/3BboNGGANS97ntU7BOQQ98R4rmnaiy6uh2Xxm xr8dx0r197Y0g== From: Sasha Levin To: david@kernel.org, akpm@linux-foundation.org, kylebot@openai.com, ljs@kernel.org, muchun.song@linux.dev, rppt@kernel.org, lance.yang@linux.dev, osalvador@suse.de, peterx@redhat.com, linmiaohe@huawei.com, lokeshgidra@google.com, liam@infradead.org Cc: stable@vger.kernel.org Subject: FAILED: patch "[PATCH] mm/userfaultfd: only allocate anon_vma in CoW mappings" failed to apply to 7.3-stable tree Date: Sat, 7 Nov 2026 05:05:31 -0500 Message-ID: <20261107050530-failed-7.3-514c9247db30@kernel.org> X-Mailer: git-send-email 2.53.0 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-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The patch below does not apply to the 7.3-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-7.3.y git checkout FETCH_HEAD git cherry-pick -x 514c9247db305922591d806ec65d3c3fe420538d # git commit -s git send-email --to '' --in-reply-to '20261107050530-failed-7.3-514c9247db30@kernel.org' --subject-prefix 'PATCH 7.3.y' 'HEAD^..' Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From 514c9247db305922591d806ec65d3c3fe420538d Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Wed, 14 Oct 2026 13:53:11 +0200 Subject: [PATCH] mm/userfaultfd: only allocate anon_vma in CoW mappings find_vma_and_prepare_anon() can end up allocating an anon_vma in VMAs that are not CoW mappings, which is wrong. If we have a MAP_SHARED R/O file mapped, we lack VM_SHARED (but do have VM_MAYSHARE) and lack VM_MAYWRITE. While uffd later rejects such mappings (uffd registration requires VM_MAYWRITE, see comment in validate_dst_vma) find_vma_and_prepare_anon() still wrongly allocates an anon vma before it validates the vma. This in turn later confuses copy_page_range()->vma_needs_copy() such that we end up calling copy_hugetlb_page_range() with ranges that actually do not contain *any* per-pagetable information that would require copying, which is the basis for PMD-table sharing in the first place. copy_hugetlb_page_range() should not have to worry about shared PMD tables at all: it doesn't make any sense to copy page tables that are shared, as they can be fully recreated later. Ending up in the function with shareable page tables is the real issue. If a destination PMD table is shared in copy_hugetlb_page_range(), it might get concurrently unshared as we are not holding relevant locks, resulting in us using a page table that is no longer mapped and possibly freed after calling: dst_pte = huge_pte_alloc(dst, dst_vma, addr, sz); To fix it, do not allocate an anon_vma in non-CoW mappings and add a safety guard to copy_hugetlb_page_range(), making sure that we never end up messing with shared PMD tables in there. Before commit 867a43a34ff8a ("userfaultfd: use per-vma locks in userfaultfd operations") we would always validate the VMA before allocating an anon_vma, and consequently never wrongly allocate an anon_vma. As uffd_lock_vma() is part of the same lookup machinery and also contains a misleading VM_SHARED check, change that one as well directly for consistency. A follow-up cleanup will stop taking the hugetlb_vma_lock_read(src_vma) lock in copy_hugetlb_page_range() entirely. Further, the usage of VM_SHARED in userfaultfd code should be cleaned up later to focus on CoW vs. non-CoW mappings. Link: https://lore.kernel.org/20261014-copy_hugetlb_page_range-v1-1-5b68e03fe7fe@kernel.org Fixes: 867a43a34ff8 ("userfaultfd: use per-vma locks in userfaultfd operations") Signed-off-by: David Hildenbrand (Arm) Signed-off-by: Andrew Morton Reported-by: Kyle Zeng Reviewed-by: Lorenzo Stoakes (ARM) Reviewed-by: Kyle Zeng Tested-by: Kyle Zeng Acked-by: Muchun Song Acked-by: Mike Rapoport (Microsoft) Tested-by: Lance Yang Cc: Oscar Salvador Cc: Peter Xu Cc: Miaohe Lin Cc: Lokesh Gidra Cc: Liam R. Howlett Cc: --- mm/hugetlb.c | 24 ++++++++++++------------ mm/userfaultfd.c | 5 ++--- 2 files changed, 14 insertions(+), 15 deletions(-) diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 27e8136b18150..da5d04edf7c10 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4973,10 +4973,11 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, raw_write_seqcount_begin(&src->write_protect_seq); } else { /* - * For shared mappings the vma lock must be held before - * calling hugetlb_walk() in the src vma. Otherwise, the - * returned ptep could go away if part of a shared pmd and - * another thread calls huge_pmd_unshare. + * Shared mappings only need copying when we could have + * information stored in page tables (e.g., userfaultfd PTE + * bits or markers), which is incompatible with PMD sharing. + * Still take the hugetlb VMA lock for now to satisfy + * hugetlb_walk()'s locking requirements. */ hugetlb_vma_lock_read(src_vma); } @@ -4984,6 +4985,13 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, last_addr_mask = hugetlb_mask_last_page(h); for (addr = src_vma->vm_start; addr < src_vma->vm_end; addr += sz) { spinlock_t *src_ptl, *dst_ptl; + + if (WARN_ON_ONCE(want_pmd_share(src_vma, addr) || + want_pmd_share(dst_vma, addr))) { + ret = -EINVAL; + break; + } + src_pte = hugetlb_walk(src_vma, addr, sz); if (!src_pte) { addr |= last_addr_mask; @@ -4995,14 +5003,6 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src, break; } -#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING - /* If the pagetables are shared, there is nothing to do */ - if (ptdesc_pmd_is_shared(virt_to_ptdesc(dst_pte))) { - addr |= last_addr_mask; - continue; - } -#endif - dst_ptl = huge_pte_lock(h, dst, dst_pte); src_ptl = huge_pte_lockptr(h, src, src_pte); spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING); diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c index da67d35cd9546..405f2d72f204e 100644 --- a/mm/userfaultfd.c +++ b/mm/userfaultfd.c @@ -115,8 +115,7 @@ struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm, vma = vma_lookup(mm, addr); if (!vma) vma = ERR_PTR(-ENOENT); - else if (!(vma->vm_flags & VM_SHARED) && - unlikely(anon_vma_prepare(vma))) + else if (vma_is_cow_mapping(vma) && unlikely(anon_vma_prepare(vma))) vma = ERR_PTR(-ENOMEM); return vma; @@ -145,7 +144,7 @@ static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm, * We know we're going to need an anon rmap, so check that * early. */ - if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma_has_anon_rmap(vma))) + if (vma_is_cow_mapping(vma) && unlikely(!vma_has_anon_rmap(vma))) vma_end_read(vma); else return vma; -- 2.53.0