From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1794418258; b=YS+EyMxy6Qe4FiDR1GqoX8tQQOlnYYu7QK2JAKnPoUWhIkk2JI5xPPJY4VSDnBDuvLfN yvBINUWroYcVbr2dRagKpRtOs+LJHmK/Z5Pdl9tThmijbPiCTnY369b3uKuDLxU8sZY2D cjnhmS/6Ai6gZ0ulgp6fy87yrnuFgB1t6uqsmuv1mIUsJb9cDtoJYViYGFClZ10AVYsFV Pq/FCSNp5WoLbALEI4YtzyT4GZclXGInza2jK+FEq0RK/8v0ipvQVvFM7n+UlTZ17g568 EDFD8N6srKDBiJQ7UiiHtxqUYhF3boLsjJVXYaZG2GTLiSJUeKkV+JQB1eg2irBTtuA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794418258; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=JV5GVKOLEyaBHZnDjhlOtWRQQrsO3dwgvOGbPw+xeI4=; b=ZyOgApuXKSEimq6AZeu/1166RQl0lDUQMIToOdjKkPhwA7nZ/OTUERleRcakIP8A661q tfIHLp6XP0SOts5TXA+Hi0JnjidIS9+bWHX0ZyAs+Z+fdwEmLRZ/vprovb3fmfSfy0Qas ape+Go1bp4EWPb1jVLE5xdll5P4TtxKKlRqSTgw3q7v65InliknyTtZs4K+g2VWwYqN4R 9qAMTuxNIJk9AbD5LMyde5CnmbrxMEx8c5QQUr4x9POhR84Q4FtD0BdxshPvrCWmoQMcj +0MNZfplM/a6UsiuxbxLNZmC3RzIo0nCle7w6WJrwHf8V9srD27Uuwa4w1TuWox0CMQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=iobE4ZKR; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8F9AA606A32A for ; Wed, 11 Nov 2026 17:30:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=iobE4ZKR Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7533F1F00A05; Wed, 11 Nov 2026 17:30:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794418258; bh=JV5GVKOLEyaBHZnDjhlOtWRQQrsO3dwgvOGbPw+xeI4=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=iobE4ZKR9B+xaUzzMKBTIJhdlAtXVktJlP4nOR+AxQiJvpSAdTl4F7qCr36l6Av+g UIDy66DH2j6m1/gVzv3O6xLoPRCHCsWOnjjarpbEEJn+I1ggfACgujrj22w95VdItl ZkEUDNfZYayd6qGFp+Q59DzYyz8e/plJObYvKqWwlG2DlYvNeD4XvU1UZIhxhh//kY 4PsNvmim3bNdoIPYijKFAYdWvjEsYgoImDaq8B9O23byV5/oTWjGitHTxGrdcM17+N yYbwsdv0TkyEWZkbpI9c6KRu7TLXLU5KCNnA5xP4nd84TWpA7sVQS62lSiCeqef1wU rexsn7HWFHFmQ== From: Sasha Levin To: stable@vger.kernel.org Cc: "David Hildenbrand (Arm)" , Josef Bacik , "Lorenzo Stoakes (ARM)" , Xu Xin , Muhammad Usama Anjum , Sasha Levin Subject: [PATCH 5.15.y] mm/madvise: fix data loss from MADV_FREE on a KSM page Date: Wed, 11 Nov 2026 12:30:56 -0500 Message-ID: <20261111173037.3570025-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261109202343-failed-5.15-22d043c1da48@kernel.org> References: <20261109202343-failed-5.15-22d043c1da48@kernel.org> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: "David Hildenbrand (Arm)" [ Upstream commit 22d043c1da48d6c7274f9dd900714b6d58b7b9c6 ] MADV_FREE can clear the dirty flag of a singly mapped KSM folio. The folio remains in the stable tree and can gain new mappings without being dirtied again. Once marked lazyfree, reclaim can discard data that those mappings still need. KSM always marks a folio dirty when converting it to a KSM folio in try_to_merge_one_page(). Marking a folio lazyfree clears PG_swapbacked but leaves PG_dirty unchanged. Preserving PG_dirty makes reclaim restore PG_swapbacked instead of discarding the folio. This also protects folios that were already lazyfree when KSM converted them. Skip KSM folios before clearing their dirty flag, checking under the folio lock to serialize with KSM conversion. Fixes: 854e9ed09ded ("mm: support madvise(MADV_FREE)") Cc: stable@vger.kernel.org Reported-by: Josef Bacik Reviewed-by: Lorenzo Stoakes (ARM) Reviewed-by: Xu Xin Tested-by: Muhammad Usama Anjum Link: https://patch.msgid.link/20261031-fixes_core-v3-34-d6437171ecc3@kernel.org Signed-off-by: David Hildenbrand (Arm) [ sashal: Adapted the folio-based KSM guard to the existing page-based APIs. ] Signed-off-by: Sasha Levin --- mm/madvise.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/mm/madvise.c b/mm/madvise.c index 367220e1fe52a..779bcf78c6a66 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -654,6 +654,15 @@ static int madvise_free_pte_range(pmd_t *pmd, unsigned long addr, if (PageSwapCache(page) || PageDirty(page)) { if (!trylock_page(page)) continue; + /* + * KSM pages can gain new mappings at any time, so we must + * not clear their dirty flag. + */ + if (PageKsm(page)) { + unlock_page(page); + continue; + } + /* * If page is shared with others, we couldn't clear * PG_dirty of the page. -- 2.53.0