From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CD65B2108 for ; Mon, 24 Apr 2023 13:34:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 55184C433EF; Mon, 24 Apr 2023 13:34:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1682343280; bh=0F5eQlGxdY6rAWgVPlo8eM1iLlhEB//90tLNeN/pz0g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=k2w/12RzUTpVeR2NziIRS9zHNZ5yiWuSumgnEHAITMU6WVXjr2ya97kJunMUQdQ0y XFMdzvreXL+HAgLUhBNPpYtrhQsHaidHcsoOKFMklr7G7VEULlEAAL/ZkZm+2kpXpL YeOPuAU1QCncVVR0u1Ic4Zp8/EtYlJvH1Ny6LP8E= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Peter Xu , David Hildenbrand , Yang Shi , Andrea Arcangeli , Axel Rasmussen , Mike Rapoport , Nadav Amit , Andrew Morton Subject: [PATCH 5.10 35/68] mm/khugepaged: check again on anon uffd-wp during isolation Date: Mon, 24 Apr 2023 15:18:06 +0200 Message-Id: <20230424131129.014396671@linuxfoundation.org> X-Mailer: git-send-email 2.40.0 In-Reply-To: <20230424131127.653885914@linuxfoundation.org> References: <20230424131127.653885914@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit From: Peter Xu commit dd47ac428c3f5f3bcabe845f36be870fe6c20784 upstream. Khugepaged collapse an anonymous thp in two rounds of scans. The 2nd round done in __collapse_huge_page_isolate() after hpage_collapse_scan_pmd(), during which all the locks will be released temporarily. It means the pgtable can change during this phase before 2nd round starts. It's logically possible some ptes got wr-protected during this phase, and we can errornously collapse a thp without noticing some ptes are wr-protected by userfault. e1e267c7928f wanted to avoid it but it only did that for the 1st phase, not the 2nd phase. Since __collapse_huge_page_isolate() happens after a round of small page swapins, we don't need to worry on any !present ptes - if it existed khugepaged will already bail out. So we only need to check present ptes with uffd-wp bit set there. This is something I found only but never had a reproducer, I thought it was one caused a bug in Muhammad's recent pagemap new ioctl work, but it turns out it's not the cause of that but an userspace bug. However this seems to still be a real bug even with a very small race window, still worth to have it fixed and copy stable. Link: https://lkml.kernel.org/r/20230405155120.3608140-1-peterx@redhat.com Fixes: e1e267c7928f ("khugepaged: skip collapse if uffd-wp detected") Signed-off-by: Peter Xu Reviewed-by: David Hildenbrand Reviewed-by: Yang Shi Cc: Andrea Arcangeli Cc: Axel Rasmussen Cc: Mike Rapoport Cc: Nadav Amit Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- mm/khugepaged.c | 4 ++++ 1 file changed, 4 insertions(+) --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -622,6 +622,10 @@ static int __collapse_huge_page_isolate( result = SCAN_PTE_NON_PRESENT; goto out; } + if (pte_uffd_wp(pteval)) { + result = SCAN_PTE_UFFD_WP; + goto out; + } page = vm_normal_page(vma, address, pteval); if (unlikely(!page)) { result = SCAN_PAGE_NULL;