From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 9CE4546C4B0; Fri, 7 Aug 2026 15:05:45 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786115149; cv=none; b=aP57V4pZBinE5ff4PFjm9qOdF+arV7w7xSHBfAIeW164Uu92cfFWIU8LUwUL5Z4P/g6y19a3WAt68/ubtr9hRRfJLCEqM4VLCZSZGkLsSXRff3eMfBcIKV8iy5vk7hKqeOQ7gAXk2xDKLFS139H/uvgNG/BMCd/S/ejMBwsTpLo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786115149; c=relaxed/simple; bh=zAvra07XjkQCyLh7JmaFzHkB38EGOPXyqljdgQ7SP5M=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Wk0Z/eHgFwzG0lotsvJdgbbxvUhiRCiAUZMFFYG3sUrFEkBBWtrAmq3MKUOtxm7/DqtjXt+ji2wmbyoiBla3vCIrM34BFhLcFmUVp28s5b1seeUdBWYKqUlw/jGb2+UzrEAmItAuxKVwhLwCfxK3aRKxGXXXHYBhTxsA3O+oaUQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=YT7zPCRW; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="YT7zPCRW" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5EBCB1F000E9; Fri, 7 Aug 2026 15:05:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1786115144; bh=MFpY/6oJWaYgRtqL+fqMX2ZyOfi1kn9QV1r295Lphr0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=YT7zPCRWgG3lOsoc90wmhb89xFHGm5JIivQQX7vG2aG4vFEFut9atAROtIL2TWYpC 4R4+cGoDEyrKrBUhvgZGJAFZzSX4uwGszbf/vtOy3KLsjNlzxFHwfZpD5/Cc2a6VBo ryl8K6frterCRysTVmUxyZ4EQQKac3NJB3gX/xMA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Kiryl Shutsemau , Sashiko AI review , Muhammad Usama Anjum , "David Hildenbrand (Arm)" , Peter Xu , Jann Horn , "Liam R. Howlett" , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Pedro Falcato , Shuah Khan , Suren Baghdasaryan , Vlastimil Babka , Zenghui Yu , Andrew Morton Subject: [PATCH 6.18 172/396] fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes Date: Fri, 7 Aug 2026 16:35:32 +0200 Message-ID: <20260807143428.011302747@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260807143424.272339768@linuxfoundation.org> References: <20260807143424.272339768@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kiryl Shutsemau (Meta) commit 40de8160ca7f67d14619ee0351ce5d68fc4a237a upstream. PAGEMAP_SCAN reports an unpopulated PTE in a uffd-wp VMA as written, but a range with no page table at all -- a PMD hole -- is skipped: pagemap_scan_pte_hole() tests p->cur_vma_category, which never carries PAGE_IS_WRITTEN, so the hole is neither reported nor (under PM_SCAN_WP_MATCHING) armed. In a uffd-wp VMA, WP_UNPOPULATED installs uffd-wp markers when protecting a range, allocating page tables as needed, so an unpopulated slot is treated as written -- see the pte_none() handling in pagemap_page_category(). A missing marker therefore means the range was zapped, e.g. via MADV_DONTNEED. This applies to anon and shmem VMAs. An anonymous THP is write-protected in place as a huge PMD, so a full-PMD MADV_DONTNEED clears it to pmd_none -- a hole with no page table -- and pagemap_scan_pte_hole() misses it. For a MAP_PRIVATE|MAP_ANON mapping MADV_DONTNEED has fill-with-zeros semantics, so a write-tracking checkpoint/migration tool (e.g. CRIU) treats the range as unchanged and keeps its previous contents; after restore or live migration the process reads stale data instead of zeroes -- data corruption. Report a hole in a non-hugetlb uffd-wp VMA as written, matching the pte_none handling in pagemap_page_category(); the existing PM_SCAN_WP_MATCHING path then arms it via uffd_wp_range(). hugetlb is excluded: pagemap_hugetlb_category() reports an empty hugetlb entry (huge_pte_none) as not-written, unlike pagemap_page_category(), which reports pte_none as written. pagemap_scan_pte_hole() fires for a hugetlb slot only when it has no page table; keeping that not-written matches how an allocated-but-empty hugetlb entry reads, so the hole and the empty-entry cases agree within the VMA. Link: https://lore.kernel.org/20260715144234.442721-2-kirill@shutemov.name Fixes: 2bad466cc9d9 ("mm/uffd: UFFD_FEATURE_WP_UNPOPULATED") Signed-off-by: Kiryl Shutsemau Reported-by: Sashiko AI review Closes: https://sashiko.dev/#/patchset/20260707151349.92143-1-kirill@shutemov.name Tested-by: Muhammad Usama Anjum Acked-by: David Hildenbrand (Arm) Cc: Peter Xu Cc: Jann Horn Cc: Liam R. Howlett Cc: Lorenzo Stoakes Cc: Michal Hocko Cc: Mike Rapoport Cc: Pedro Falcato Cc: Shuah Khan Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Zenghui Yu Assisted-by: Claude:claude-fable-5 Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- fs/proc/task_mmu.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -2918,12 +2918,28 @@ static int pagemap_scan_pte_hole(unsigne { struct pagemap_scan_private *p = walk->private; struct vm_area_struct *vma = walk->vma; + unsigned long categories; int ret, err; - if (!vma || !pagemap_scan_is_interesting_page(p->cur_vma_category, p)) + if (!vma) return 0; - ret = pagemap_scan_output(p->cur_vma_category, p, addr, &end); + /* + * In a uffd-wp VMA an unpopulated range is treated as written: + * uffd-wp registration populates page tables and installs markers + * with WP_UNPOPULATED, so a missing marker means the range was + * zapped. See the pte_none() handling in pagemap_page_category(). + * + * hugetlb differs, see pagemap_hugetlb_category(). + */ + categories = p->cur_vma_category; + if (userfaultfd_wp(vma) && !is_vm_hugetlb_page(vma)) + categories |= PAGE_IS_WRITTEN; + + if (!pagemap_scan_is_interesting_page(categories, p)) + return 0; + + ret = pagemap_scan_output(categories, p, addr, &end); if (addr == end) return ret;