From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f44.google.com (mail-wm1-f44.google.com [209.85.128.44]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 6A3E2277C81 for ; Tue, 30 Sep 2025 07:13:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.44 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759216393; cv=none; b=Cq8usurnMMScmOn4Qce/ZG05Ik/O8kTk9YOMgVzumcIIFgzDH3zTyDjoy4Q8xuYRkm/4jWSBGjyTwdc0r5MX9oHMuS5G6CifEF+a1uQ+hZY7ITjEDxtBAZCd3yls4GFN8aBTn05t40ZwedYIEnJzzxr5wledygrhjfpUrDkZBYw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1759216393; c=relaxed/simple; bh=jZLUYO9y0S453l34VftfAEuNf7vhvQMizNgY3IHOQ3s=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=pwYWTiuwMVszY6ygTj8/e9l444qE7UoMSex62hv9kS96VrPwwzycY30oEtpWBf1PCKQ8c8P7h/JKhDAjPu5Qyojm99Am8RzHGF0OK4a4yzomfTWnVTD5R8vWdyZgvVnlnLYBZeTjUXJSYyGCJa+bFjUzBGRFQCnOet9B96TjmBU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=gmail.com; arc=none smtp.client-ip=209.85.128.44 Authentication-Results: smtp.subspace.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Received: by mail-wm1-f44.google.com with SMTP id 5b1f17b1804b1-46e3af7889fso31071805e9.2 for ; Tue, 30 Sep 2025 00:13:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1759216390; x=1759821190; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=RJg+MB8jkyhooYHl7VPWRbhLVwCzgwHPNjrxfT41vz8=; b=KQA0oSz0oZNsgdDpnDLpFeQkcV+dLEvt9oRG5qbUBLc18g9OOjlaMhyS9bWXEKf2aR GLZ76qGb68jPUtaANV5zb5mMr7wDqcqYxYDVl7JYyVuyHo7b+pseRuypvHihi1hFeAJs WRAJTGLI8+94mftpIqLtLkOnHxVy4oikVrFDH8cAPN2ID0whp+4E2b/Eppz7tphGRqyT jDUhj0RCUhYEaJvSPbhYOip+X2ompWtKjAsvU6dFwbztM8Qu8cwD4DUPWq2HUyjHw3jY QCPrazkXPN4A7uQHICrYzla+p81bUT3FVfd8U86RB8K57wr/qeJh/hFxX8bTjHZMGJTf Z1iw== X-Forwarded-Encrypted: i=1; AJvYcCV7zfjrbgLJdI6zt24/VDlhq9lXn2jvQeScs/a1Bc8PyefVW8i7ZSBPPrOiQlpS6WLnPFY0Pd8=@vger.kernel.org X-Gm-Message-State: AOJu0Yy8Aau2bmg4LUT9iRIysf+HZlJENYr1fvWQmIqTCc3XtycRmuli 5DP1J6ZdHIKnHoyRMesdE3GFo/274bbz6BrI4DM2JTdxApum6VVt+vD8 X-Gm-Gg: ASbGnct+y6XojR49/IpORIs0mayFAJFEAqAwQ8x2Rwexg7GDTaQmvTHlZPtTplbuinA sS3xqUBLrrRFDKqbmS0S40ZqF0oyTzNWSRNlysuOUsxJuAPBpM0zdlJBa824t3/fIL1YqXvYNQR a+Z/z1s5xqTTOBeyJQteDadIqMtNuOx+/E8awo2pxRrhEB332S5R1yF7rhPGUc8DzYo2INTsGj4 2eLvkZPFpI0v7LKxfgdQHq3xVwZWbfTyfxfXxygnYE+Eo60uxkNo2m88XnJvaCYaSVXrmElDBkW aINoTikJiUlabFOZnAD8uk9nYcJ5PFdLomYOWYHal81gc3+QKJ5iUV5w021Y52OCgcO25D3YmPi iVtiCT20eJES1nOgzr1cr0yxDW4i2epdw0bbfIOWSnE6q7uvp/A== X-Google-Smtp-Source: AGHT+IHG/vdhpkUdLGzDD/hQegsFD5o72BWBQNk08ly8bjkRBa9wOlUTaVnXFyckUgCALWtyUUhxsA== X-Received: by 2002:a05:600c:8b58:b0:45d:e326:96fb with SMTP id 5b1f17b1804b1-46e32a17d2bmr190697065e9.30.1759216389605; Tue, 30 Sep 2025 00:13:09 -0700 (PDT) Received: from localhost.localdomain ([2a09:0:1:2::301b]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-46e56f64d06sm42221855e9.12.2025.09.30.00.13.00 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Tue, 30 Sep 2025 00:13:09 -0700 (PDT) From: Lance Yang To: akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com Cc: peterx@redhat.com, ziy@nvidia.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, ryan.roberts@arm.com, dev.jain@arm.com, npache@redhat.com, riel@surriel.com, Liam.Howlett@oracle.com, vbabka@suse.cz, harry.yoo@oracle.com, jannh@google.com, matthew.brost@intel.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, usamaarif642@gmail.com, yuzhao@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ioworker0@gmail.com, stable@vger.kernel.org, Lance Yang Subject: [PATCH v4 1/1] mm/rmap: fix soft-dirty and uffd-wp bit loss when remapping zero-filled mTHP subpage to shared zeropage Date: Tue, 30 Sep 2025 15:10:53 +0800 Message-ID: <20250930071053.36158-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Lance Yang 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. Cc: Fixes: b1f202060afe ("mm: remap unused subpages to shared zeropage when splitting isolated thp") Suggested-by: David Hildenbrand Suggested-by: Dev Jain Acked-by: David Hildenbrand Reviewed-by: Dev Jain Signed-off-by: Lance Yang --- v3 -> v4: - Minor formatting tweak in try_to_map_unused_to_zeropage() function signature (per David and Dev) - Collect Reviewed-by from Dev - thanks! - https://lore.kernel.org/linux-mm/20250930060557.85133-1-lance.yang@linux.dev/ v2 -> v3: - ptep_get() gets called only once per iteration (per Dev) - https://lore.kernel.org/linux-mm/20250930043351.34927-1-lance.yang@linux.dev/ v1 -> v2: - Avoid calling ptep_get() multiple times (per Dev) - Double-check the uffd-wp bit (per David) - Collect Acked-by from David - thanks! - https://lore.kernel.org/linux-mm/20250928044855.76359-1-lance.yang@linux.dev/ mm/migrate.c | 16 ++++++++++------ 1 file changed, 10 insertions(+), 6 deletions(-) diff --git a/mm/migrate.c b/mm/migrate.c index ce83c2c3c287..21a2a1bf89f7 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -296,8 +296,7 @@ bool isolate_folio_to_list(struct folio *folio, struct list_head *list) } 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; @@ -306,7 +305,7 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, 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)) @@ -322,6 +321,12 @@ static bool try_to_map_unused_to_zeropage(struct page_vma_mapped_walk *pvmw, 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)); @@ -344,7 +349,7 @@ static bool remove_migration_pte(struct folio *folio, while (page_vma_mapped_walk(&pvmw)) { rmap_t rmap_flags = RMAP_NONE; - pte_t old_pte; + pte_t old_pte = ptep_get(pvmw.pte); pte_t pte; swp_entry_t entry; struct page *new; @@ -365,12 +370,11 @@ static bool remove_migration_pte(struct folio *folio, } #endif 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)) -- 2.49.0