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=1794063632; b=g3MIm7AUPdvrVGgT+H9YLTHinsVlBlv6o8MqZk0wzqu9wjWoM+BjxkLNP9gf7j3n4lws O7qEBZdC4vDBWLdGODtjoTK83gZ537bbKiPcJUZGLGpkeI2OTx9YdYsJUXRNP+nF64nIE 3fa003xppAkhamnn3urAR7XvfyWO9UW/sO3OhTxtf6nSQ5/tnXifRTjVviD4rIcX38EHi yXRxxoRgrY//2biC7n7gwNeQ9gU8Bnbaxnwb3lxQ6106OVlNnsWJQ+UsZoR6BUhKHyLHB j1w8SMhwdm86Km4qios3OfanXr3XLhCDl14dhFeBlVQhOTQiQ7NIrBSAUQk4cZWncPw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794063632; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=rvC1BRZ8e9sqXVCP3QCIXVWfNjaPMZvKcVB/KE2fHqM=; b=2yerESn1xrFk9xnNSV1q4A3uliNn2cP1ToBSRwIQ/V6x8mgRennxjxpF4bbHNjTe7qwL 2tyVCklzEu/phcaVBZoNBCOe+dnjieo11l7Fm7h0KwH4m3xtHoCFV5SDhhVtTxZFC2dQZ yBkh8xF0m6OGgDHYWF7UsLLbOL/bX0+3iP5g37bsH1e4FJEhl3NiQeFLWcrY43MomUC5h 0GlIu44hlIXTOM3YArvghSY91Qju1Zqq0nY7NS/6addxGskz/HlSl+odlUyJ+HbtVWW/p pXbehyjs9GE6QKomQN7dBBnegQrmbWcLrnjepnSXEgIa5bk7elKNi5/YOiXJinme1aA== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=1oEofURa; 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 25D34606EEAB; Sat, 7 Nov 2026 15:00:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=1oEofURa Received: by smtp.kernel.org (Postfix) with ESMTPSA id ABB8A1F0089F; Sat, 7 Nov 2026 15:00:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794063632; bh=rvC1BRZ8e9sqXVCP3QCIXVWfNjaPMZvKcVB/KE2fHqM=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=1oEofURadr7+aGNWucmbn+rQA2sVABqJTeS/RUiKThdLDY406iUJatudwhZQj1I9+ Dj6jBtO3vQjfg05iS5aJz/cg191EhHcuZq+P9s9v3iW0f3b8YIRb5jBKjpcRfEjNVO jRHHArrek/HyRepv21JdPPz1RfaxO2+SV81tDGNQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, 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 6.18 749/869] mm/madvise: atomically clear the young bit on THP MADV_COLD Date: Sat, 7 Nov 2026 08:57:11 -0500 Message-ID: <20261107134918.158959290@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134852.069646174@linuxfoundation.org> References: <20261107134852.069646174@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore 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 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ 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 bb02220e1959b..729d8f2f07fd8 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -428,10 +428,7 @@ 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