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 552893B14D0; Thu, 9 Jul 2026 21:59:37 +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=1783634378; cv=none; b=hYC6rO8pzcnoGmEe8AliDwqzpuO4gr8kpX+e8FJWmBvn3kQ8Rbv4TOpEmy4CCLq45POmm+grrbc9aO2YzJoVTu/XZHl7+3o92wWoK5J1zO+a6Gn1kueu7jygGf2uEwTNs7pdlhdDVdyRrQ/ks+tMP2kmNeifWNtE93CnV3HdwIE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783634378; c=relaxed/simple; bh=nZEfOqakGhrPhkXxd8r6kHvrN4AfqAqTnSXyBK6zciY=; h=Date:To:From:Subject:Message-Id; b=Rdzl3Ae6vtahpVuNY8jFl7HilXuP4Dludh+6NP8f2awnsLkUICkQU+IEIZCewbxLqgtvO+ADMRwh4KZybpxN0M4YjYWR5ocQxydQgCd2dQXicgHwWfdPJO7GiI0uvWp7AlIGYGIi9ry0o/62b64WDjdQPm7WLCV9GU3ExEgHESM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=uxN3wKaK; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="uxN3wKaK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C8BA41F000E9; Thu, 9 Jul 2026 21:59:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783634376; bh=5tK1sldEP4KMoyI7+NHCua1UXH3emOrx5R2z7xRRzu8=; h=Date:To:From:Subject; b=uxN3wKaKMrR0KGa0XZ2GPrd2BL5eOKWdDDDhTHjx8GhVkUzfuBplJnk7bHmCQ/GBX LE6svK/3J187X3hRiInLvpjG5QqDuXgtxFEivr0EmLaAGiUgw9AdeV4ZSYkrCi+haY /F9SsaZaM2jK5aC/QaNGM+XmWBnJIF1Pl1yPUW7E= Date: Thu, 09 Jul 2026 14:59:36 -0700 To: mm-commits@vger.kernel.org,vbabka@kernel.org,usama.anjum@collabora.com,surenb@google.com,stable@vger.kernel.org,shuah@kernel.org,sashiko-bot@kernel.org,rppt@kernel.org,pfalcato@suse.de,peterx@redhat.com,mhocko@suse.com,ljs@kernel.org,liam@infradead.org,jannh@google.com,david@kernel.org,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes.patch added to mm-hotfixes-unstable branch Message-Id: <20260709215936.C8BA41F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes has been added to the -mm mm-hotfixes-unstable branch. Its filename is fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via various branches at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there most days ------------------------------------------------------ From: "Kiryl Shutsemau (Meta)" Subject: fs/proc/task_mmu: fix PAGEMAP_SCAN written state for PMD holes Date: Thu, 9 Jul 2026 13:16:29 +0100 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. MADV_DONTNEED has fill-with-zeros semantics: it changes the contents of the range to zeroes (a subsequent read maps the zero page), which write tracking must report as written. 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 -- and the zeroing goes unreported. A write-tracking checkpoint/migration tool (e.g. CRIU) then treats the range as unchanged and keeps its previous contents, so 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. Add a pagemap_ioctl selftest covering the anon-THP PMD-hole case. Link: https://lore.kernel.org/20260709121629.205562-1-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 Cc: Muhammad Usama Anjum Cc: Peter Xu Assisted-by: Claude:claude-fable-5 Cc: David Hildenbrand 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: Signed-off-by: Andrew Morton --- fs/proc/task_mmu.c | 27 ++++++++- tools/testing/selftests/mm/pagemap_ioctl.c | 56 ++++++++++++++++++- 2 files changed, 80 insertions(+), 3 deletions(-) --- a/fs/proc/task_mmu.c~fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes +++ a/fs/proc/task_mmu.c @@ -3049,12 +3049,35 @@ 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); + /* + * An unpopulated range with no page table -- e.g. a 2MB anon THP + * dropped via MADV_DONTNEED, which pagemap_page_category() never sees + * -- reads as written on a uffd-wp VMA, matching the pte_none case + * there. Reporting it also lets the PM_SCAN_WP_MATCHING arming below + * install markers (uffd_wp_range() allocates the page table under + * WP_UNPOPULATED), so the next scan sees it clean until re-written. + * + * 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. This + * path 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 two agree within the VMA. + */ + 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; --- a/tools/testing/selftests/mm/pagemap_ioctl.c~fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes +++ a/tools/testing/selftests/mm/pagemap_ioctl.c @@ -1102,6 +1102,59 @@ static void unpopulated_scan_test(void) munmap(mem, mem_size); } +/* + * A 2MB anon THP dropped with MADV_DONTNEED leaves a pmd_none hole with no + * page table, which pagemap_page_category() never sees. PAGEMAP_SCAN must + * still report it as written on a uffd-wp VMA, via pagemap_scan_pte_hole(). + */ +static void unpopulated_thp_hole_test(void) +{ + long npages, written = 0, ret, i; + struct page_region regions[16]; + char *area, *mem; + + if (!hpage_size) { + ksft_test_result_skip("%s THP not supported\n", __func__); + return; + } + npages = hpage_size / page_size; + + /* Get a PMD-aligned range so the range can be a single THP. */ + area = mmap(NULL, 2 * hpage_size, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (area == MAP_FAILED) + ksft_exit_fail_msg("%s mmap failed\n", __func__); + mem = (char *)(((unsigned long)area + hpage_size - 1) & ~(hpage_size - 1)); + + memset(mem, 1, hpage_size); + if (madvise(mem, hpage_size, MADV_COLLAPSE) || + !check_huge_anon(mem, 1, hpage_size)) { + ksft_test_result_skip("%s could not form a THP\n", __func__); + munmap(area, 2 * hpage_size); + return; + } + + wp_init(mem, hpage_size); + + /* Drop the whole PMD: it is cleared to a pmd_none hole. */ + if (madvise(mem, hpage_size, MADV_DONTNEED)) + ksft_exit_fail_msg("%s MADV_DONTNEED failed\n", __func__); + + ret = pagemap_ioctl(mem, hpage_size, regions, 16, 0, 0, + PAGE_IS_WRITTEN, 0, 0, PAGE_IS_WRITTEN); + if (ret < 0) + ksft_exit_fail_msg("%s scan failed\n", __func__); + for (i = 0; i < ret; i++) + written += LEN(regions[i]); + + ksft_test_result(written == npages, + "%s pmd-hole reported written (%ld of %ld)\n", + __func__, written, npages); + + wp_free(mem, hpage_size); + munmap(area, 2 * hpage_size); +} + int sanity_tests(void) { unsigned long long mem_size, vec_size; @@ -1610,7 +1663,7 @@ int main(int __attribute__((unused)) arg if (!hugetlb_setup_default(4)) ksft_print_msg("HugeTLB test will be skipped\n"); - ksft_set_plan(118); + ksft_set_plan(119); page_size = getpagesize(); hpage_size = read_pmd_pagesize(); @@ -1790,6 +1843,7 @@ int main(int __attribute__((unused)) arg /* 18. Unpopulated pte scan-path consistency */ unpopulated_scan_test(); + unpopulated_thp_hole_test(); close(pagemap_fd); ksft_finished(); _ Patches currently in -mm which might be from kas@kernel.org are fs-proc-task_mmu-fix-pagemap_scan-written-state-for-unpopulated-ptes.patch mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.patch fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes.patch mm-decouple-protnone-helpers-from-config_numa_balancing.patch mm-rename-uffd-wp-pte-bit-macros-to-uffd.patch mm-rename-uffd-wp-pte-accessors-to-uffd.patch userfaultfd-test-uffd-vma-flags-through-the-vma_flags_t-api.patch mm-add-vm_uffd_rwp-vma-flag.patch mm-add-mm_cp_uffd_rwp-change_protection-flag.patch mm-preserve-rwp-marker-across-pte-rewrites.patch mm-handle-vm_uffd_rwp-in-khugepaged-rmap-and-gup.patch userfaultfd-add-uffdio_register_mode_rwp-and-uffdio_rwprotect-plumbing.patch mm-userfaultfd-add-rwp-fault-delivery-and-expose-uffdio_register_mode_rwp.patch mm-pagemap-add-page_is_accessed-for-rwp-tracking.patch userfaultfd-add-uffd_feature_rwp_async-for-async-fault-resolution.patch userfaultfd-add-uffdio_set_mode-for-runtime-sync-async-toggle.patch documentation-userfaultfd-document-rwp-working-set-tracking.patch