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=1794352245; b=Tp8SJqXouxkma2M32xrlE8W6NebuHaF9oTfjAE6v43SDL3FH6xKYhaN0zUIRxYDz+9L5 qJo2BJcA/UH10e5DN5KX+LKy1wMkrlDfeLz0wsaGeDKZnNus+sDNEsgoFCUmVGN7svQfr Oa4NxbjzwZ+xXoZPfWTehNgKi1n2VZQf+U7JZxP1Z0duPPb0yvlMJ0Rv4y+6KfDDxgQo/ ibqT9QkgIL+WjNHH3zEWyQtdHD0WOO9csG9E8jEZDDaE/Qxjs9Pk+P0ldS9tjw32co3VE 7pmzNakFH7sHnLgQ/eUY7O/mrdYa4mhC0+VcRoWetWIApkA20f9vqRRUL9WaXgq98DA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794352245; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=ok3n3s1PieUsRKr4lKqMJm3zdz4Lx3ky2IaLFteFDMc=; b=nQ0W690XDwoSnPfIarzgbjCUR/rVnSglP98XCc3VmKvqiKjySQAvJY5GxpqfkBNNZBYH 67SFh4WPwnJYSmvYyQnPpY0tzz2Mj6rQ8roOBff7wmlNjFBUyHGBNZJJg1tHR4O/s6oH0 faUX9NSv8b0A3N6g6hnDuyXKGtfQMy3nMyVs4mhGB3HiaPoCtSlcjPkdSoUVcwyVplkQF dFTqRI1IsxTCS+yNP43U2c7el8wtCWTW6xLE2EA1bGfLkhG+pVDCr5cC79bCkQmuYe2uR DK1iNO1pdNMDWs5zjCWfz5HYG0KUS4JpyQVv2kTZBlTY5R+scHdio1nZsXy8GGt6LZQ== 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=RuXy3QEh; 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 9F9E7606A321 for ; Tue, 10 Nov 2026 23:10:44 +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=RuXy3QEh Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8E8AE1F0093C; Tue, 10 Nov 2026 23:10:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794352244; bh=ok3n3s1PieUsRKr4lKqMJm3zdz4Lx3ky2IaLFteFDMc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=RuXy3QEhGaYpSF47QE2JnMH1OIzvD4LH4Kicy8Rfgwba6iHhy3RdBwFR4fhoRajoi ZY6RQHX2ouQSHInIm/1aHgDanJeCBMDezBjllaIEFb2GTDcBT+gGkIYboG3dd/dQxh byXWK3i3m8oXCDMtK2Ji6XdHqw6YV0Tm5VrYcbVjuRuWuCfKP0S3zsv8kcBGLpFKJc ibzkXsppP5FqfIpupOyAwOwTeBOO3Pn+gZ4bWMXmw98yppi08ywvXBVZhU7FhYiPA2 J/u7s92HEvmSHvDSL8ePGTjQ2YeyIlX28L51tFVIwGQJpWnXd/MpxDk9+bm0jMDpIg o5wIUju4T9lfg== 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 5.15.y] mm/madvise: atomically clear the young bit on THP MADV_COLD Date: Tue, 10 Nov 2026 18:10:41 -0500 Message-ID: <20261110231006.82713-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107061139-failed-5.15-246c8cc33438@kernel.org> References: <20261107061139-failed-5.15-246c8cc33438@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: [ sashal: adjusted context for the pmd_young() check without the !pageout guard ] 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 367220e1fe52a..3079da08c19de 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -363,10 +363,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *pmd, } if (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