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=1794351866; b=kjzsd7lqbHPxxNT8Az9U+U7RS+oScpA2Zv5xpwNr9F90A9dJCrNjzurUEi/np02RbIiR h3aYEHAJYr+HXvYXx+AGuUN8h0WKYg+LkLK+Qpl/f/GR1amMjKiSWr0YaWoMW1HCUdHVT aG8CWLCoaMrymEZRQweLFcnD4NhTfm+OO8tcQ7HDDskDU0PNC2VJpFM50Vcz2nfWkH7JA eLjPo8nqS9mUOlYfHuwPdn9U1ArxosaH3THleGgNox0TyDsREEd8vZQ7MDntieo4XQMUg VFaZAbS7VsSF2fJoqgVnEYah2KLky5GsOCSisRNXaTavVSNZC4Qr9xq84O+yGy2eamg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794351866; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=ptbrXyjXjn9ybewZ72JuSBgD9Xkgj7iYAbI+rx4WeLM=; b=zSuPmqRrcKIaL3MPO9wl/DsoKT3RUUuhKfZeIjpzfYtrJvjZQKQ9x2aOXt9Fzr26s8Kh HP73q8eHuC68ERGF60+eyXNAApUNtwvm18IRRv8DGHt3UJxipUninL0+6qoT/cn7rkD5l QKDH5Ebyq7S2zWJD+GN4q7V1CT9utJYVC5nm6NJcj8VBRsoOFSYZUEHuyJLYHW2gZuVGZ fDjeucug6oPXWuejejEAMtxgvizm+U2Eue00QGJ/dTyQbYTLLeWKFpWeMKLld1gNeH9rG zEH2n+x4pl4zTCj1KH5UYx696Kiy0AkMxLm0pY91scdbb/ypv2AoqizLMOkBf96Z08Q== 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=bDLcMZu2; 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 1A8FC606A31C for ; Tue, 10 Nov 2026 23:04:26 +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=bDLcMZu2 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 5F41D1F0093C; Tue, 10 Nov 2026 23:04:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794351866; bh=ptbrXyjXjn9ybewZ72JuSBgD9Xkgj7iYAbI+rx4WeLM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bDLcMZu2CBq7qx60kUT9HTr7OWAWwqC75wECD2mA+G5W6/XuiADzQR6smjUBqyRXw /Of4yvmCKHT03VAyXWTdbyMuU/e0abCIu00BEshgEObxtqKlI3fkSoMTPa6G8t17U/ X+h3tqbYIBGiRbdar0ykxFJ13kNoBN0fO9GWJogTvA3AGoDLybhV24ojTWfoO36TV7 dioh8l/1FajBLtxavwQr5X972yFeIW5OXYjMNLd/hncCdFC2iKt+XsS9yxcJQE0Tel mfsKppSM4oMma8ilZGsbHClTJX8H3fyRVoPbHuC9Vyxq+qiRLpjC2V3LZvwMpyY1jH PwyKz73eq8RNw== 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 6.1.y] mm/madvise: atomically clear the young bit on THP MADV_COLD Date: Tue, 10 Nov 2026 18:04:23 -0500 Message-ID: <20261110230356.8288-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107055439-failed-6.1-246c8cc33438@kernel.org> References: <20261107055439-failed-6.1-246c8cc33438@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: Retained pmd_young(orig_pmd) without the !pageout guard because the corresponding reclaim optimization is absent. ] 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 b271cc1b48edb..5640bacba5384 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -379,10 +379,7 @@ 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