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 F0DEA3A451D; Thu, 9 Jul 2026 03:37:38 +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=1783568260; cv=none; b=lp1eYrQHx7A3lFH/SQxg/1QHRT+vDApn0ebTcHYy1XZslcGOWOR2YTzWrVEwUDonG98COFksUFjkBH0Dr1DxdjP+08wEA7IJCtkN+EOZbt0y1vn6tMmPc1k6SUklV2VOGqF2O8uFPO4PwvYMiUWVTrPIiU6257FTWp9CDXJiAP8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783568260; c=relaxed/simple; bh=ulJaWT+5oJhNMhEGMOGXbRD7JkIgCS52zawAbmsyQC0=; h=Date:To:From:Subject:Message-Id; b=YJNMhDzougRYx+WsRp9GBMOQF4WoC340OjWmEPctw5p7nyqrfXIuBF5sHJLZa6iCORo4UsrNV3EedXT7mTKsw1uipxbox+AZq+BmbDCbb/AKqL11lSPxXIw+gMZGoxluET709XbAa82ky6Cc7ReZmt2QEgpSl+gctRoTlU2UKmc= 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=yni3jNOI; 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="yni3jNOI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 730E11F000E9; Thu, 9 Jul 2026 03:37:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783568258; bh=WZ0AsjbPVZUXfBnoQrNoZ516yTkW8VzLOQlKGSOrlno=; h=Date:To:From:Subject; b=yni3jNOIp0wx3VNgyfuiiGnlqvqEIzUiUAwm0XrDVvzv6NloD5VeWHlwezjeKqsvH Trwd4JLszz5wCARS5SxaJP86LqDSu5xhG2Sw5ii4Co48GfzWfGdH5elNm5eqAEmkSv mW0MIiIH8g5Wdq2p1SngOokEGHBOAOxxFPwITif4= Date: Wed, 08 Jul 2026 20:37:38 -0700 To: mm-commits@vger.kernel.org,stable@vger.kernel.org,sashiko-bot@kernel.org,peterx@redhat.com,osalvador@suse.de,muchun.song@linux.dev,david@kernel.org,kas@kernel.org,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.patch added to mm-hotfixes-unstable branch Message-Id: <20260709033738.730E11F000E9@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.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: mm/hugetlb: fix swap entry corruption when clearing uffd-wp at fork() Date: Wed, 8 Jul 2026 10:01:10 +0100 copy_hugetlb_page_range() clears the uffd-wp bit of migration and hwpoison entries with huge_pte_clear_uffd_wp(), which operates on the present-PTE bit position. Swap entries keep the uffd-wp state elsewhere -- the migration branch reads and sets it with pte_swp_uffd_wp() and pte_swp_mkuffd_wp() -- and the present-PTE position falls into the swap payload. On x86-64 it lands in the inverted swap offset, where a naturally-aligned hugetlb PFN always has the affected bit set, so the clear advances the encoded PFN by two pages. No userfaultfd needs to be involved: the clear is guarded only by the child VMA not being uffd-wp registered, so a plain fork() with an in-flight hugetlb migration entry (or a poisoned hugetlb page) corrupts the entry copied into the child. Instrumenting the clear and forking after MADV_HWPOISON on a 2MB anon hugetlb page shows: offset before=120e00 offset after =120e02 The fallout is mostly latent: rmap walks match migration entries by folio range and remove_migration_pte() rebuilds the PTE from the folio, so a within-folio PFN skew heals once migration completes. But any path that re-encodes the corrupted offset -- e.g. hugetlb_change_protection() rewriting a writable migration entry via make_readable_migration_entry(swp_offset(entry)) -- propagates it. Migration entries legitimately carry uffd-wp, so clear it with pte_swp_clear_uffd_wp(), matching copy_nonpresent_pte() and move_huge_pte(). A hwpoison entry, on the other hand, never carries the uffd-wp bit: it is installed fresh by make_hwpoison_entry() (try_to_unmap_one() does not preserve uffd-wp on the hwpoison path) and hugetlb_change_protection() leaves hwpoison entries untouched. There was nothing to clear there, only the corruption, so drop the clear entirely. Link: https://lore.kernel.org/20260708090110.136162-1-kirill@shutemov.name Fixes: bc70fbf269fd ("mm/hugetlb: handle uffd-wp during fork()") Signed-off-by: Kiryl Shutsemau Reported-by: Sashiko AI review Closes: https://lore.kernel.org/all/20260703140011.99E601F000E9@smtp.kernel.org/ Suggested-by: David Hildenbrand Acked-by: David Hildenbrand (Arm) Assisted-by: Claude:claude-fable-5 Cc: Muchun Song Cc: Oscar Salvador Cc: Peter Xu Cc: Signed-off-by: Andrew Morton --- mm/hugetlb.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-) --- a/mm/hugetlb.c~mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork +++ a/mm/hugetlb.c @@ -4929,8 +4929,12 @@ again: softleaf = softleaf_from_pte(entry); if (unlikely(softleaf_is_hwpoison(softleaf))) { - if (!userfaultfd_wp(dst_vma)) - entry = huge_pte_clear_uffd_wp(entry); + /* + * A hwpoison entry never carries the uffd-wp bit: it is + * installed fresh by make_hwpoison_entry() and + * hugetlb_change_protection() leaves it untouched, so + * there is nothing to clear for the child. + */ set_huge_pte_at(dst, addr, dst_pte, entry, sz); } else if (unlikely(softleaf_is_migration(softleaf))) { bool uffd_wp = pte_swp_uffd_wp(entry); @@ -4948,7 +4952,7 @@ again: set_huge_pte_at(src, addr, src_pte, entry, sz); } if (!userfaultfd_wp(dst_vma)) - entry = huge_pte_clear_uffd_wp(entry); + entry = pte_swp_clear_uffd_wp(entry); set_huge_pte_at(dst, addr, dst_pte, entry, sz); } else if (unlikely(pte_is_marker(entry))) { const pte_marker marker = copy_pte_marker(softleaf, dst_vma); _ 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 fs-proc-task_mmu-fix-pagemap_scan-written-state-for-pmd-holes.patch mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.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 selftests-mm-add-userfaultfd-rwp-tests.patch documentation-userfaultfd-document-rwp-working-set-tracking.patch