From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 8D1B02110E; Tue, 30 Sep 2025 21:51:36 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759269096; cv=none; b=Mba3JmzC2bg7P/j5Oo9egaNRMevy1hrCLW1wDsFOEAMuK9W+b4DjfeKpl9YvsZWpxkXmVHfEDgoPsOar1ThNff81ChnDAme7lZbMAI+7VuVcy55/xi7rP/a39wuC5FQJEGkPztP8Xhr3cUgs6SxR+7yxJ58pTbqIdWwJYlWYOTs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759269096; c=relaxed/simple; bh=bslu/l2CcgWsTKNdAVrk3vTbm98RpTdFT8fD9YRhjFM=; h=Date:To:From:Subject:Message-Id; b=htKyCY+oatDka5oxbF1Z0X/lZZuUdK3MPt0JRKSJfvktP2LU1lj+urBN8jPyKoQsRklr01roW0FZdgsXDxTfmfFxiT36pNa2NtIZB6pycZWu6w885rmW8d0nyBXte7pxjWjuPq2mfy4aKBpN9OV7uW05vo1KLnLvvZo0iJjlGYI= 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=qOGwF/Ly; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="qOGwF/Ly" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EC142C4CEF0; Tue, 30 Sep 2025 21:51:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1759269096; bh=bslu/l2CcgWsTKNdAVrk3vTbm98RpTdFT8fD9YRhjFM=; h=Date:To:From:Subject:From; b=qOGwF/LyRJbK0V8i+olAnqSYl3oIV8/6ewzXNg53a5X4O0g/NIn228j8OXhswBx3S OAUF1arma1VKB4UKXYVZxNcb3e66dXb69iBBXWAcK4hs8iP1EQvFHBHLwUxktNefnr 42B+HpcjnIUjZ4OteLncJdj5mi6AAwN5uCmKQ6Cc= Date: Tue, 30 Sep 2025 14:51:35 -0700 To: mm-commits@vger.kernel.org,ziy@nvidia.com,yuzhao@google.com,ying.huang@linux.alibaba.com,vbabka@suse.cz,usamaarif642@gmail.com,stable@vger.kernel.org,ryan.roberts@arm.com,riel@surriel.com,rakie.kim@sk.com,peterx@redhat.com,npache@redhat.com,matthew.brost@intel.com,lorenzo.stoakes@oracle.com,liam.howlett@oracle.com,joshua.hahnjy@gmail.com,jannh@google.com,gourry@gourry.net,dev.jain@arm.com,david@redhat.com,byungchul@sk.com,baolin.wang@linux.alibaba.com,baohua@kernel.org,apopple@nvidia.com,lance.yang@linux.dev,akpm@linux-foundation.org From: Andrew Morton Subject: + mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage.patch added to mm-hotfixes-unstable branch Message-Id: <20250930215135.EC142C4CEF0@smtp.kernel.org> Precedence: bulk X-Mailing-List: mm-commits@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: The patch titled Subject: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage.patch This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage.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 the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Lance Yang Subject: mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage Date: Tue, 30 Sep 2025 16:10:40 +0800 When splitting an mTHP and replacing a zero-filled subpage with the shared zeropage, try_to_map_unused_to_zeropage() currently drops several important PTE bits. For userspace tools like CRIU, which rely on the soft-dirty mechanism for incremental snapshots, losing the soft-dirty bit means modified pages are missed, leading to inconsistent memory state after restore. As pointed out by David, the more critical uffd-wp bit is also dropped. This breaks the userfaultfd write-protection mechanism, causing writes to be silently missed by monitoring applications, which can lead to data corruption. Preserve both the soft-dirty and uffd-wp bits from the old PTE when creating the new zeropage mapping to ensure they are correctly tracked. Link: https://lkml.kernel.org/r/20250930081040.80926-1-lance.yang@linux.dev Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") Signed-off-by: Lance Yang Suggested-by: David Hildenbrand Suggested-by: Dev Jain Acked-by: David Hildenbrand Reviewed-by: Dev Jain Acked-by: Zi Yan Cc: Alistair Popple Cc: Baolin Wang Cc: Barry Song Cc: Byungchul Park Cc: Gregory Price Cc: "Huang, Ying" Cc: Jann Horn Cc: Joshua Hahn Cc: Liam Howlett Cc: Lorenzo Stoakes Cc: Mariano Pache Cc: Mathew Brost Cc: Peter Xu Cc: Rakie Kim Cc: Rik van Riel Cc: Ryan Roberts Cc: Usama Arif Cc: Vlastimil Babka Cc: Yu Zhao Cc: Signed-off-by: Andrew Morton --- mm/migrate.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) --- a/mm/migrate.c~mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage +++ a/mm/migrate.c @@ -297,8 +297,7 @@ bool isolate_folio_to_list(struct folio } static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, - struct folio *folio, - unsigned long idx) + struct folio *folio, pte_t old_pte, unsigned long idx) { struct page *page = folio_page(folio, idx); pte_t newpte; @@ -307,7 +306,7 @@ static bool try_to_map_unused_to_zeropag return false; VM_BUG_ON_PAGE(!PageAnon(page), page); VM_BUG_ON_PAGE(!PageLocked(page), page); - VM_BUG_ON_PAGE(pte_present(ptep_get(pvmw->pte)), page); + VM_BUG_ON_PAGE(pte_present(old_pte), page); if (folio_test_mlocked(folio) || (pvmw->vma->vm_flags & VM_LOCKED) || mm_forbids_zeropage(pvmw->vma->vm_mm)) @@ -323,6 +322,12 @@ static bool try_to_map_unused_to_zeropag newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address), pvmw->vma->vm_page_prot)); + + if (pte_swp_soft_dirty(old_pte)) + newpte = pte_mksoft_dirty(newpte); + if (pte_swp_uffd_wp(old_pte)) + newpte = pte_mkuffd_wp(newpte); + set_pte_at(pvmw->vma->vm_mm, pvmw->address, pvmw->pte, newpte); dec_mm_counter(pvmw->vma->vm_mm, mm_counter(folio)); @@ -365,13 +370,13 @@ static bool remove_migration_pte(struct continue; } #endif + old_pte = ptep_get(pvmw.pte); if (rmap_walk_arg->map_unused_to_zeropage && - try_to_map_unused_to_zeropage(&pvmw, folio, idx)) + try_to_map_unused_to_zeropage(&pvmw, folio, old_pte, idx)) continue; folio_get(folio); pte = mk_pte(new, READ_ONCE(vma->vm_page_prot)); - old_pte = ptep_get(pvmw.pte); entry = pte_to_swp_entry(old_pte); if (!is_migration_entry_young(entry)) _ Patches currently in -mm which might be from lance.yang@linux.dev are hung_task-fix-warnings-caused-by-unaligned-lock-pointers.patch mm-thp-fix-mte-tag-mismatch-when-replacing-zero-filled-subpages.patch mm-rmap-fix-soft-dirty-and-uffd-wp-bit-loss-when-remapping-zero-filled-mthp-subpage-to-shared-zeropage.patch mm-clean-up-is_guard_pte_marker.patch