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=1794350834; b=nAcHZWwjiUaxuD9FSyuUdDglEJmfj/ZjmK7Zedd1jicEOB0He42QiC+6BKpNxBhUPHxC j4nzhgd+BH1FOA4NxC63dLpk4Qc5ajDxbnFLsfQvhRKJI2vwqmCQ7LIlh0ySoA0+E5Com MoNBeCW/adTSbUL2LsTEawYVXeNe4uw54Uj9Bdtyvwh7jfN+n48mLwpUN+1ojPnUAzM4t zO9Lw+T949yczkOW3fFNB9TxYgpkh26aLw0/tR+uDO6hRR1zndBHzYNN8+4C3hmt4qV1v FTyXJCki0D1gYzyNJXz9l/wNWT5hVQhzBDTT6FTFpHQ1hrno+kKD5uv2tILD4NAhg6Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794350834; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=zWzERcXx19jQFlRJzHBmIdKsZ87oY2HndjwKvsnilsU=; b=mo/W+uNkU0JhREicfYnVIN0PaxX6qoIZ9fwfe5FkCn+6t/NR59I8rRwspfUmrlbsnggL Y4scF3WYKYt5tkPoxl9Op2fO/iE5qKoPbdjN+kWCQJ2ROTvLMHYX4yiBHZF815bqk/YIX dgJgwHMX2KK91zKe8N26YDtSuWAiqEFoqXNByPg5MWxtlxJtRr0ENDXJX95yj6JM+GFVy u0JpNifBLfL2HSUtefH4Gbq3sqE76YnQI6MpG8FKKUZm1QtLH3XpdTHE/y/vsPOFS6pes hGI0dgNC3M6l8seRJ5lIhBcwZgr5eTNTwDTMO4hX4z5lI9r00iZksLd2HSb5kBgI9KQ== 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=h9Ed1GoN; 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 CB0B4606A32A for ; Tue, 10 Nov 2026 22:47:13 +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=h9Ed1GoN Received: by smtp.kernel.org (Postfix) with ESMTPSA id D69781F00A06; Tue, 10 Nov 2026 22:47:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794350833; bh=zWzERcXx19jQFlRJzHBmIdKsZ87oY2HndjwKvsnilsU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=h9Ed1GoN9eS1BCLDsGoZRexHtz4ITZq2F3td0BYJPqblh1pT57zSe09X2THPTPQ+g 9NpxyVkFbDhWdjcIDW7WbZ2ivzMHVEMv7TOvPYOPZEfgeWjJ7gbzG7i0UdzjY2vl8i 1Fv7OvVbmbBVzme5b8eybt2uBq99WSWSla4+sjvFDgzSx8KM7bcVgGNhOPjDBADEcT VUPGcUDjKq55goFy73Pi8KrmLp/iuutV1UdmGvjqbkvDsy6N76oXDQ0P8wwJ81FUbo BXBHoVdA/N5aoLXBnk9JiTa6/odArPVXA3+4hVdvdtnURFDgrS41SG84izZJ+/S6Qp qUskspzuDykUw== From: Sasha Levin To: stable@vger.kernel.org Cc: Pedro Falcato , Andrew Morton , Samarth Narang , "Gregory Price (Meta)" , Zi Yan , "Lorenzo Stoakes (ARM)" , "David Hildenbrand (Arm)" , SJ Park , "Liam R. Howlett" , Vlastimil Babka , Jann Horn , Minchan Kim , Michal Hocko , Johannes Weiner , Sasha Levin Subject: [PATCH 6.6.y 2/2] mm/madvise: atomically clear the young bit on THP MADV_COLD Date: Tue, 10 Nov 2026 17:47:09 -0500 Message-ID: <20261110224525.4066997-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261110224525.4066997-1-sashal@kernel.org> References: <20261107053858-failed-6.6-246c8cc33438@kernel.org> <20261110224525.4066997-1-sashal@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: Pedro Falcato [ Upstream commit 246c8cc33438a71c28f9b86baa492d9a0a130316 ] As-is, madvise_cold_or_pageout_pte_range() discards the hardware young bit by invalidating the PMD, doing pmd_mkold() and subsequently writing to the pmd again. However, it does so in a racy manner, looking at a possibly-stale snapshot. It's entirely possible that a write elsewhere set the hardware D bit, which this logic now loses. Fix it by using pmdp_test_and_clear_young(). This is an atomic modification of the PMD entry, and thus safe against any possible racing writes. As a (nice) side-effect, this elides one non-required TLB flush in pmdp_invalidate(). This bug can interact with the swapping system in complicated ways, leading to data loss. For instance, if a folio is marked lazyfree, but was later read from, and then MADV_COLD'd while racing a write to that same THP, dropping the dirty bit may lead to data loss as reclaim/MADV_PAGEOUT drops the "clean" anon folio: T0 T1 ================================================================ MADV_FREE(thp) | folio marked lazyfree | read(thp) | PMD marked young by hardware | | MADV_COLD(thp) write(thp) | if (pmd_young(pmd)) { PMD marked dirty by hardware | set(pmdp, pmd_mkold(pmd)); MADV_PAGEOUT/reclaim | dirty bit may or may not be | set | reclaim/pageout may drop | the folio | Link: https://lore.kernel.org/20261013191719.95502-1-pfalcato@suse.de Fixes: 9c276cc65a58 ("mm: introduce MADV_COLD") Signed-off-by: Pedro Falcato Signed-off-by: Andrew Morton Reported-by: Samarth Narang Closes: https://lore.kernel.org/linux-mm/20261011132227.413217-1-samarth.colleges@gmail.com/ Reviewed-by: Gregory Price (Meta) Acked-by: Zi Yan Reviewed-by: Lorenzo Stoakes (ARM) Acked-by: David Hildenbrand (Arm) Reviewed-by: SJ Park Cc: Liam R. Howlett Cc: Vlastimil Babka Cc: Jann Horn Cc: Minchan Kim Cc: Michal Hocko Cc: Johannes Weiner Cc: Signed-off-by: Sasha Levin --- mm/madvise.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/mm/madvise.c b/mm/madvise.c index 7d3a9c4b993f0..d9f55db95a9b1 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -404,10 +404,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, } if (!pageout && pmd_young(orig_pmd)) { - pmdp_invalidate(vma, addr, pmd); - orig_pmd = pmd_mkold(orig_pmd); - - set_pmd_at(mm, addr, pmd, orig_pmd); + pmdp_test_and_clear_young(vma, addr, pmd); tlb_remove_pmd_tlb_entry(tlb, pmd, addr); } -- 2.53.0