From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 9986E606A324 for ; Mon, 26 Oct 2026 23:23:16 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=lists.infradead.org header.i=@lists.infradead.org header.a=rsa-sha256 header.s=bombadil.20210309 header.b=qwmFNF7D; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=XfqLS+Hl DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Cc:To:In-Reply-To:References :Message-Id:Content-Transfer-Encoding:Content-Type:MIME-Version:Subject:Date: From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Unsubscribe-Post: List-Owner; bh=+1JYyOVK17L4M/YeGKfhk/Lxzr76gDTGDeCEv+yAeac=; b=qwmFNF7DxeWyW3 iXc8VPZX63V/sFzNN515wW6CN/DQH8pbqWHzhh3AidPsB+XNRMlYwtkMG0+Fr/3ilvKeQDPApOTFT WCBiqYLODSy5gOlVjzgoPLR+cs7og9b68OmfKM7EHgXPOYQQOIKoQ2ILanxH95D/CO2VceCY5p8I4 CPYDL6/Y+MppYHxqHyea/rJQwTaZ7ougJ0p+IukKZAZiQ07Z0Xq0QNqM7cz5jxvB4Cb2L5AkHQ+o/ 0chnogQtf/+4wYQL9ZvuA9S9MQYzSFKWeQF6M+scCvv6IhVAIHF4xNg8svZceAgKGDko1I86EF6jT 5u8O6U+FcA7Upm8u3UJQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLU28-00000003Q2h-0xqs; Mon, 26 Oct 2026 23:23:16 +0000 Received: from sea.source.kernel.org ([2600:3c0a:e001:78e:0:1991:8:25]) by bombadil.infradead.org with esmtps (Exim 4.100.1 #2 (Red Hat Linux)) id 1xLU27-00000003Q2X-0qlX for kexec@lists.infradead.org; Mon, 26 Oct 2026 23:23:15 +0000 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id DF9B9418A5; Mon, 26 Oct 2026 23:23:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4086B1F01829; Mon, 26 Oct 2026 23:22:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793056994; bh=+1JYyOVK17L4M/YeGKfhk/Lxzr76gDTGDeCEv+yAeac=; h=From:Date:Subject:References:In-Reply-To:To:Cc; b=XfqLS+HlbsjgMnNRoaz++2jtQC1Na277NB03VKlGtUyrHgM+UcBK81mvCEQXk6SEn uoUWk/Y0LokQHfua8ALu7xo3TimdxKbFw+ync5x9x0414hpGK5euj90aDiThH/i2g6 gltMFd0YkJRSCGbzjhMIA1svIJg0OdjzS+VJrfdV55Ru5CcTX1Km3zOSH9bit+hmH0 nXtTvSU+BWI1pGaDlkzv7qX0PMn63J0KkAM5JF7EYYmHtIGdHKXb/weVqb341vnhNN LtvoefAcxQzn7M5h/ljiIxS0k3AY0Dobha0DvHSvTN45tBuUaJN6bUn9HpN5iNYDaL BChgtuF/TGxrw== From: "David Hildenbrand (Arm)" Date: Tue, 27 Oct 2026 00:17:37 +0100 Subject: [PATCH 17/46] mm/khugepaged: preserve dirty bits when collapsing PTE-mapped THPs X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Message-Id: <20261027-fixes_core-v1-17-6f74bec9a5bb@kernel.org> References: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> In-Reply-To: <20261027-fixes_core-v1-0-6f74bec9a5bb@kernel.org> To: Andrew Morton , Johannes Weiner , Michal Hocko , Qi Zheng , Shakeel Butt , Lorenzo Stoakes , Kairui Song , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Baoquan He , Baolin Wang , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Kees Cook , Peter Zijlstra , Jann Horn , Pedro Falcato , Hugh Dickins , Pasha Tatashin , Pratyush Yadav , "Matthew Wilcox (Oracle)" , Jan Kara , Zi Yan , Lance Yang , Rik van Riel , Harry Yoo , Alistair Popple , Nico Pache , Ryan Roberts , Dev Jain , Usama Arif , Kiryl Shutsemau , Matthew Brost , John Hubbard , Peter Xu , Will Deacon , "Aneesh Kumar K.V" , Nick Piggin , Oscar Salvador , Minchan Kim , Muchun Song , Xu Xin , Chengming Zhou , Chris Li , Kemeng Shi , Nhat Pham , Youngjun Park , Gregory Price , Joshua Hahn , Rakie Kim , Ying Huang , Jason Gunthorpe Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kexec@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-arch@vger.kernel.org, linux-cxl@vger.kernel.org, Chris Mason , stable@vger.kernel.org, "David Hildenbrand (Arm)" X-Mailer: b4 0.16.0 X-Developer-Signature: v=1; a=openpgp-sha256; l=2036; i=david@kernel.org; h=from:subject:message-id; bh=/nGuewYAfnIDGwfYFGkywdM27AcdGHIuhx2sh7J1pmM=; b=owGbwMvMwCF2/OVpCdfQ3ZWMp9WSGLLu35/6OOtCmHDt6RCT9t8MvwO2SXtqiyk4FhS5aFTuX MPD2Pu4o5SFQYyDQVZMkSUo+L7By5fraqvd+Jhh5rAygQxh4OIUgInszmf4Z8e1UOzQzKxPdqpf L849defDtaQtSYFsyhXzPZYxX3zefZDhn2bE7/KyvsKAtbrnVr0+WPQz3O36FpVnmdnVGpfN+PP n8AMA X-Developer-Key: i=david@kernel.org; a=openpgp; fpr=1BD9CAAD735C4C3A460DFCCA4DDE10F700FF835A X-BeenThere: kexec@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "kexec" X-Spam-Status: No, score=-19.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=ham autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 From: Chris Mason try_collapse_pte_mapped_thp() clears PTEs without transferring their dirty bits to the folio. A shmem read fault can map a clean folio writable, so a later store only dirties the PTE. Losing that dirty bit allows reclaim to discard modified data. The assumption that regular files are read-only is also obsolete since commit 1b6444331bebb ("mm/khugepaged: enable clean pagecache folio collapse for writable files"). In any case, transferring PTE dirty bits to the folio when removing mappings (and while the folio is still mapped) is the right thing to do. Use get_and_clear_ptes() to collect the dirty bits and mark the folio dirty before unmapping it. Update the comment. This was reproduced with shmem using MADV_COLLAPSE followed by MADV_PAGEOUT. Fix generated by an LLM and sent by Chris Mason in private. Fixes: 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP") Fixes: 1b6444331bebb ("mm/khugepaged: enable clean pagecache folio collapse for writable files") Cc: stable@vger.kernel.org Signed-off-by: Chris Mason [ david: adjust comment; simplify description; cover file-thp as well ] Signed-off-by: David Hildenbrand (Arm) --- mm/khugepaged.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 04d9bb21ff524..dd17c3dae8006 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -1995,9 +1995,10 @@ static enum scan_result try_collapse_pte_mapped_thp(struct mm_struct *mm, unsign /* * Must clear entry, or a racing truncate may re-remove it. * TLB flush can be left until pmdp_collapse_flush() does it. - * PTE dirty? Shmem page is already dirty; file is read-only. */ - clear_ptes(mm, addr, pte, nr_batch_ptes); + ptent = get_and_clear_ptes(mm, addr, pte, nr_batch_ptes); + if (pte_dirty(ptent)) + folio_mark_dirty(folio); folio_remove_rmap_ptes(folio, page, nr_batch_ptes, vma); nr_mapped_ptes += nr_batch_ptes; } -- 2.43.0