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=1794333255; b=APSiSL69jnGA5QtNrDhSRRIZol0WLxjg872TLGPAXQ5opubnDnFSyjI9NhYKVXh0osyw ckHJsNyv2kKpj9+PSOB00+OIJ/zjb6QA+90S7KpjqVcXcfPSf/inK2v94v+hbB2bCeo4K jtHmB+ZBrDHmZBGs76cHp7r0V6noRHJc5nNmyNcxys5nAi31cDHi/Siuyliz5KxCU7crg dpOKRS5NGbJ6mvnZeaSb8aTliawJuKBfmjarylE6eUtrxfFKYi4YNOIdGpY3UrS7zxlTG oF+6niShRYzMAOka5LLwyGzViaqLO4mGBQbS0kbwAlb6eJU5rajKWTtTcuTbRn+wFsQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794333255; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=vzbjzKuQrzRPtBdYMB1Q6wfdhJUh/ZNDkq6muU6Gcig=; b=Y7g9daz0WSoo9xQ983JBn4khf6hA0JsSpnmlcLVJdNDPhcJ9hUSiNq5Q5h1PjcXraeyv vHAO8NvmSniTTjHeRDQMfqcRsiNf2NeFFIKTE7UQDthxbg587U5iPMiXFmFYAIMy7Avuf Kjjl5ZxNJgllkaajqBTJZ69/BJeHjzHSFMKRtoTc9KY0IyFe0RgHwVWuZtdTtZLMKvOXI SGDz0o5i5/oxTbErH0NRA+2lqnblqY82Ul54MvsMqMHKsxNpfGi7sh361AnDflh7s5hK0 J6rLU4hV5+35yZ9L0ZejW/H+wr2ZqP8OIv30DppvHNDirp4v5+THYDPOnrWiqPabUWw== 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=LMfVvYBd; 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 4256D606A31C for ; Tue, 10 Nov 2026 17:54:15 +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=LMfVvYBd Received: by smtp.kernel.org (Postfix) with ESMTPSA id C6AE71F00904; Tue, 10 Nov 2026 17:54:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794333254; bh=vzbjzKuQrzRPtBdYMB1Q6wfdhJUh/ZNDkq6muU6Gcig=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=LMfVvYBdY1duRB4WdlebBA9Dh70OHjdFW2syQ5HkstKKx42PQisMGJN33QVGHLWQw 9VJxnXgkpdEnvOCN56m53jcdSvswtFrbLlMBgfUqgqwFMXOr2SKeefUu0OqN70YDTI aMA0DCgpnlkMOi65Wy3BIjF2Skx55ut2AHsYTHMCQZSm7RI4sAISaYyXmsQK/QV64G V7I95JDa6l/u8cjACTFJe3o+GJy0GCOYExmL1FY8jRnSvCrELQkRMSDNW9GQ1a76rZ yZ1vOzJ/7PeOCEuqYRPuQzeiPraPUQQkhPG25+/UcUtrp06JEWfZT0sJ3xgGESsHGM 9UqsmB0omyfTw== From: Sasha Levin To: stable@vger.kernel.org Cc: Zhiling Zou , Ren Wei , Andrew Morton , Vega , Ye Liu , Sasha Levin Subject: [PATCH 6.12.y] mm/page_table_check: skip zero pages Date: Tue, 10 Nov 2026 12:54:12 -0500 Message-ID: <20261110175354.2995296-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261107051936-failed-6.12-33afd07412a1@kernel.org> References: <20261107051936-failed-6.12-33afd07412a1@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(pfn) with is_huge_zero_folio(pfn_folio(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 2efa910eef23e..1076f8e055f31 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_folio(pfn_folio(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_folio(pfn_folio(pfn))) return; page = pfn_to_page(pfn); -- 2.53.0