From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id EFC6AC433EF for ; Wed, 18 May 2022 14:56:28 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 5EFC16B0071; Wed, 18 May 2022 10:56:28 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 59F046B0073; Wed, 18 May 2022 10:56:28 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 48E896B0074; Wed, 18 May 2022 10:56:28 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id 3AF326B0071 for ; Wed, 18 May 2022 10:56:28 -0400 (EDT) Received: from smtpin24.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id 1907B607AD for ; Wed, 18 May 2022 14:56:28 +0000 (UTC) X-FDA: 79479164856.24.F2BF559 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf07.hostedemail.com (Postfix) with ESMTP id A7F76400C9 for ; Wed, 18 May 2022 14:56:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=4Is6VMKTGS6Q+REIPQaUhYHAbJCVB2LMBP9f+Vwnyr0=; b=ZicRzH8+hsKxFUFZUGV7uh6rsr liYqq1jo/NJPjFOq45aL15fhGeuMBVY2fPnZKIydDip+x+51BJs5NLmaGT8oWGbYZbNY+K0Pyrkef 6rtOzeBsy0dtcUJ9XhADYUN1Y2oy9oXlw62lJz3I3InUErp1+tH7/lFyOSmAivKaDcxFU8jfS3PYX 5/inIxpdAkkRzXjoVhil+5k58vn049Ny8S6eWbnS3PYIDvtdMiaokBA2YBm3sYTd/JNaiZ0Wbl7n9 ZDo+9nTYLRaDzeaIcwzrVzxX+7iFsugHlQtmCGx0J+QdfouNf4S/mZbzCdefd3KPIBkiWnP0vWdHc TOCI2+AQ==; Received: from willy by casper.infradead.org with local (Exim 4.94.2 #2 (Red Hat Linux)) id 1nrL61-00Bsxi-6p; Wed, 18 May 2022 14:56:17 +0000 Date: Wed, 18 May 2022 15:56:17 +0100 From: Matthew Wilcox To: David Hildenbrand Cc: Qi Zheng , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, songmuchun@bytedance.com, zhouchengming@bytedance.com, akpm@linux-foundation.org, tglx@linutronix.de, kirill.shutemov@linux.intel.com, jgg@nvidia.com, tj@kernel.org, dennis@kernel.org, ming.lei@redhat.com Subject: Re: [RFC PATCH 00/18] Try to free user PTE page table pages Message-ID: References: <20220429133552.33768-1-zhengqi.arch@bytedance.com> <8c51d9ae-5a8e-74a9-ddc2-70b5fcd38427@bytedance.com> <37055be1-05af-f7ef-c33e-27f90fa0f9ca@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <37055be1-05af-f7ef-c33e-27f90fa0f9ca@redhat.com> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A7F76400C9 X-Stat-Signature: qnzqhgqufsm17rtmp86yeybxdwmgb9zi Authentication-Results: imf07.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=ZicRzH8+; dmarc=none; spf=none (imf07.hostedemail.com: domain of willy@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=willy@infradead.org X-Rspam-User: X-HE-Tag: 1652885778-761955 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, May 18, 2022 at 04:51:06PM +0200, David Hildenbrand wrote: > yes, I talked about the involved challenges, especially, how malicious > user space can trigger allocation of almost elusively page tables and > essentially consume a lot of unmovable+unswappable memory and even store > secrets in the page table structure. There are a lot of ways for userspace to consume a large amount of kernel memory. For example, one can open a file and set file locks on alternate bytes. We generally handle this by accounting the memory to the process and let the OOM killer, rlimits, memcg or other mechanism take care of it. Just because page tables are (generally) reclaimable doesn't mean we need to treat them specially.