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=1794334245; b=JlXYE6L1eW3m6CO40kGFd75BiMlrsbINJPS3wZJo2DIbpbsUjHgA32/b6dIXqfWZT1sX XAEIH1DXRSiTetzXiA8zSLyKfrfooJKFMYr+hfTvplDTCk7UFdCPtMxMqv0WPrvJq7p20 XOV7TfUfUeEfAjJ8+DM4cjt9emCuCWp4TU5Wqpf9Ct9QnGXXZgPZbMRWOHgA2LYepHD5h KrV06+X4LQ3+es1BCEVUz411c59Mvn6AwPqbEFvmDgrZjqmvVJXsA/KpQgXsZppyTqr3P iro/gvJKmyjkQJpfTLpWuOoF7j2bYE4zBabt35Ry/7U+XZOP5iRMZGQ6XnIn/55DxZQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794334245; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=AVeHV/0ig34Jvn/XnhURaJvAE59/0nVBt0wdtY1TPbs=; b=rpqLE4FPb0U86RwYKX4Jm2rvMvK3uJ2AhAe8dpDqGWUwIR15EFchV2Lbrtm8MFu1Iz3N YKP9XM2zkEhcBDvpLJHqCNbw75U/QYMx45/v7z/fdlj6e7JDSOCtoKm6QZveTSEToCaPh 4bi/B2jCAKruZeANi5Aq6HcXwcNFarz6pt6zrE4jxlIYqN97t2vQWkld+ess1bXGIGTE6 2uPLMttPLZDPH8Yase6ORUEV3Dh4nJz5CCSkj/QweY6FzpKlPwC5xMpkgH+aSM4BqTibz XhVEqpTpnJ6pt9nh9OHdbECpR2qguHtMKR4OfT/w+b4zIMT6Xmr/w5k9W7K6xTKWT5A== 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=bqRNYstW; 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 A1703606A326 for ; Tue, 10 Nov 2026 18:10:45 +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=bqRNYstW Received: by smtp.kernel.org (Postfix) with ESMTPSA id 607461F0089F; Tue, 10 Nov 2026 18:10:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794334245; bh=AVeHV/0ig34Jvn/XnhURaJvAE59/0nVBt0wdtY1TPbs=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=bqRNYstWTbYsjgY5TcvDF+tctoy+dcG5/+CCtX80rMEX5RbEHHjkJh+XAtj915Ipx 5b1XiucCry9t1IKHR2xzKFPdtdQwiYq0AuzocdcxD06sGJkAD1NLgrUKt9GzdVQOXX iRP0aqzjWM7K9PT/cxQgNEW6zYtyTcrL3RoY2Cnrh5HraN2tU34FHq8nK4jjpKA0/X 7vLdLv3JQFLFBG2pXy6K17wwTDSHcrvyLshlcc+ctG5wTZrOV6zlAMrBX1uTDVpDh7 30yTWoMd+EMmxMKH7vfkKS7UKKL4KQai4S/eCCG5/o06F6Ta2nQKTdttf4lNg2vhxh 9BHvW0jIyWEWg== From: Sasha Levin To: stable@vger.kernel.org Cc: Zhiling Zou , Ren Wei , Andrew Morton , Vega , Ye Liu , Sasha Levin Subject: [PATCH 6.6.y] mm/page_table_check: skip zero pages Date: Tue, 10 Nov 2026 13:10:43 -0500 Message-ID: <20261110181016.3096221-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107053208-failed-6.6-33afd07412a1@kernel.org> References: <20261107053208-failed-6.6-33afd07412a1@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: Zhiling Zou [ Upstream commit 33afd07412a1efe5b750a3fd5eb0272ebdd12761 ] page_table_check_set() accounts pages by whether they are PageAnon(). The shared zero page is a special page, not an ordinary file-backed page. Read faults on private anonymous mappings can install many read-only PTEs that point at the zero page, but page_table_check currently accounts them in file_map_count. That lets an unprivileged process populate enough zero-page mappings to overflow file_map_count and trip the BUG_ON() in page_table_check_set(). Skip zero pages in page_table_check accounting. They do not need the anonymous/file mapping conflict checks that page_table_check performs for ordinary pages, and this keeps the existing counter size and page_ext layout unchanged. Link: https://lore.kernel.org/1f8848512d2e3ded944f8d595c29faee8fdaeab0.1784645969.git.roxy520tt@gmail.com Fixes: df4e817b7108 ("mm: page table check") Signed-off-by: Zhiling Zou Signed-off-by: Ren Wei Signed-off-by: Andrew Morton Reported-by: Vega Assisted-by: Codex:gpt-5.4 Cc: Ye Liu Cc: [ sashal: Replaced unavailable is_huge_zero_pfn() with is_huge_zero_page(compound_head(pfn_to_page(pfn))). ] Signed-off-by: Sasha Levin --- mm/page_table_check.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/page_table_check.c b/mm/page_table_check.c index 75269bc47547f..4356aa8563c5b 100644 --- a/mm/page_table_check.c +++ b/mm/page_table_check.c @@ -67,7 +67,8 @@ static void page_table_check_clear(unsigned long pfn, unsigned long pgcnt) unsigned long i; bool anon; - if (!pfn_valid(pfn)) + if (!pfn_valid(pfn) || is_zero_pfn(pfn) || + is_huge_zero_page(compound_head(pfn_to_page(pfn)))) return; page = pfn_to_page(pfn); @@ -107,7 +108,8 @@ static void page_table_check_set(unsigned long pfn, unsigned long pgcnt, unsigned long i; bool anon; - if (!pfn_valid(pfn)) + if (!pfn_valid(pfn) || is_zero_pfn(pfn) || + is_huge_zero_page(compound_head(pfn_to_page(pfn)))) return; page = pfn_to_page(pfn); -- 2.53.0