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 05E2D33EC; Sun, 5 Jul 2026 02:08:28 +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=1783217310; cv=none; b=Dp2pRiO5xH0BCMGfbW5Lir1Z50vCd4uYYx1kmbyV1cNv6xInB3r8lfm//CKk4Dy07OCUGzCz7P1RmvH1+6yOLnLML7A4Xw2IK2BEsDhRCrU+bIc16gqE1EbYTre6gsZuTMxA3+PojN1n7EmG4gjK6eLihVrsLPTvUtB9Z7dXgSo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783217310; c=relaxed/simple; bh=lTaUj7uF+90n/LsGOVnBH+5mFS/xSTVXDsvE8jJZ++g=; h=Date:To:From:Subject:Message-Id; b=FJKFqwMtYBEYj3hL7X68kE9cYNB5EB2qLjSfGJX95kGm1Jfxa0IgK9CTfhYW9/CgTY9NVItervfsyWipZARYs1FhGBRyfh9VSBOHBQOGUpbf8ovSuI3n2BMkSDuI1MubR4fxLl+rVCLHTAl1MqmwoM7gPXD4aydaHDT+pPsOA9I= 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=uN+1IFvx; 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="uN+1IFvx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 93AC81F000E9; Sun, 5 Jul 2026 02:08:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1783217308; bh=nl3EQnBacKgUws6evdkNL++HkX2qCNVYd/S8Pfi4pYY=; h=Date:To:From:Subject; b=uN+1IFvxLHeKbOsJWcTb5DJpa+O2TviVGc0eQ9t06cGa2fYbyM90r/rA4HAWWQXLX pPuofPSbHueUfMnMmrM3Jc6Cuw/gUhMemu2nIkbI3qJZCJWRWE6X62B2J5okj9gGsC g/BDzkPcANEGU2AHHR//IIulEfeXq1Yl51Hg28v4= Date: Sat, 04 Jul 2026 19:08:28 -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: <20260705020828.93AC81F000E9@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: Fri, 3 Jul 2026 17:18:33 +0100 copy_hugetlb_page_range() clears the uffd-wp bit of hwpoison and migration entries with huge_pte_clear_uffd_wp(), which operates on the present-PTE bit position. Swap entries keep the uffd-wp state elsewhere -- the same branches read and set 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 hwpoison branch 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, and an hwpoison entry misidentifies which page is poisoned. Use pte_swp_clear_uffd_wp(), matching copy_nonpresent_pte() and move_huge_pte(). Link: https://lore.kernel.org/20260703161833.57416-1-kirill@shutemov.name Fixes: bc70fbf269fd ("mm/hugetlb: handle uffd-wp during fork()") Signed-off-by: Kiryl Shutsemau Assisted-by: Claude:claude-fable-5 Reported-by: Sashiko AI review Closes: https://lore.kernel.org/all/20260703140011.99E601F000E9@smtp.kernel.org/ Cc: David Hildenbrand Cc: Muchun Song Cc: Oscar Salvador Cc: Peter Xu Cc: Signed-off-by: Andrew Morton --- mm/hugetlb.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/mm/hugetlb.c~mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork +++ a/mm/hugetlb.c @@ -4918,7 +4918,7 @@ again: softleaf = softleaf_from_pte(entry); if (unlikely(softleaf_is_hwpoison(softleaf))) { 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(softleaf_is_migration(softleaf))) { bool uffd_wp = pte_swp_uffd_wp(entry); @@ -4936,7 +4936,7 @@ 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 mm-hugetlb-fix-swap-entry-corruption-when-clearing-uffd-wp-at-fork.patch