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 X-Spam-Level: X-Spam-Status: No, score=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E7347C169C4 for ; Mon, 11 Feb 2019 12:46:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BD656218A6 for ; Mon, 11 Feb 2019 12:46:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727585AbfBKMqK (ORCPT ); Mon, 11 Feb 2019 07:46:10 -0500 Received: from mga04.intel.com ([192.55.52.120]:44460 "EHLO mga04.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727328AbfBKMqJ (ORCPT ); Mon, 11 Feb 2019 07:46:09 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by fmsmga104.fm.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 11 Feb 2019 04:46:08 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.58,358,1544515200"; d="scan'208";a="143268694" Received: from linux.intel.com ([10.54.29.200]) by fmsmga004.fm.intel.com with ESMTP; 11 Feb 2019 04:46:08 -0800 Received: from [10.125.252.196] (abudanko-mobl.ccr.corp.intel.com [10.125.252.196]) by linux.intel.com (Postfix) with ESMTP id 538D75800C6; Mon, 11 Feb 2019 04:46:04 -0800 (PST) Subject: Re: [PATCH v2 1/4] perf-security: document perf_events/Perf resource control To: Thomas Gleixner Cc: Jonatan Corbet , Kees Cook , Ingo Molnar , Peter Zijlstra , Jann Horn , Arnaldo Carvalho de Melo , Jiri Olsa , Namhyung Kim , Alexander Shishkin , Andi Kleen , Mark Rutland , Tvrtko Ursulin , "kernel-hardening@lists.openwall.com" , "linux-doc@vger.kernel.org" , linux-kernel References: From: Alexey Budankov Organization: Intel Corp. Message-ID: <969b6ea5-a5bf-70b7-7031-38b07538f744@linux.intel.com> Date: Mon, 11 Feb 2019 15:46:02 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.5.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.02.2019 1:34, Thomas Gleixner wrote: > On Thu, 7 Feb 2019, Alexey Budankov wrote: > > General note: Please stay in the 80 char limit for all of the text. Yes, sure. [PATCH v2 4/4] implements wrapping at 72 columns. > >> +The perf_events system call API [2]_ allocates file descriptors for every configured >> +PMU event. Open file descriptors are a per-process accountable resource governed >> +by the RLIMIT_NOFILE [11]_ limit (ulimit -n), which is usually derived from the login >> +shell process. When configuring Perf collection for a long list of events on a >> +large server system, this limit can be easily hit preventing required monitoring >> +configuration. > > I'd move this sentence into a different paragraph and keep those related to > RLIMIT_NOFILE together. Makes sense. Let's have these two paragraphs: Open file descriptors +++++++++++++++++++++ Memory allocation +++++++++++++++++ > >> ... RLIMIT_NOFILE limit can be increased on per-user basis modifying >> +content of the limits.conf file [12]_ on some systems. > > On some systems? Well, let's avoid this subtlety and have it like: 'RLIMIT_NOFILE limit can be increased on per-user basis modifying content of the limits.conf file [12]_ .' > >> Ordinarily, a Perf sampling session >> +(perf record) requires an amount of open perf_event file descriptors that is not >> +less than a number of monitored events multiplied by a number of monitored CPUs. > > s/a number of/the number of/ Accepted. > > The ordinary use case is: > > perf CMD pile-of-events PROCESS > > which does not specify the monitored CPUs at all. Then the number of file > descriptors is NR_EVENTS * NR_ONLINE_CPUS. > >> +An amount of memory available to user processes for capturing performance monitoring > > The amount ... Accepted. > >> +data is governed by the perf_event_mlock_kb [2]_ setting. This perf_event specific >> +resource setting defines overall per-cpu limits of memory allowed for mapping >> +by the user processes to execute performance monitoring. The setting essentially >> +extends the RLIMIT_MEMLOCK [11]_ limit, but only for memory regions mapped specially > > s/specially/specifically/ Accepted. > >> +for capturing monitored performance events and related data. >> + >> +For example, if a machine has eight cores and perf_event_mlock_kb limit is set >> +to 516 KiB, then a user process is provided with 516 KiB * 8 = 4128 KiB of memory >> +above the RLIMIT_MEMLOCK limit (ulimit -l) for perf_event mmap buffers. In particular, >> +this means that, if the user wants to start two or more performance monitoring >> +processes, the user is required to manually distribute available 4128 KiB between the > > distribute the available Accepted. > >> +monitoring processes, for example, using the --mmap-pages Perf record mode option. >> +Otherwise, the first started performance monitoring process allocates all available >> +4128 KiB and the other processes will fail to proceed due to the lack of memory. >> + >> +RLIMIT_MEMLOCK and perf_event_mlock_kb resource costraints are ignored for > > constraints. Accepted. > >> +processes with the CAP_IPC_LOCK capability. Thus, perf_events/Perf privileged users > > what means perf_events/Perf ? 'perf_events/Perf privileged users' refers to the paragraph about privileged users. 'perf_events/Perf' means exact combination of the kernel subsystem (perf_events) and the privileged Perf tool (Perf) executable that enables certain group of users with performance monitoring capabilities without scope limit. > >> +can be provided with memory above the constraints for perf_events/Perf performance >> +monitoring purpose by providing the Perf executable with CAP_IPC_LOCK capability. > > Thanks, > > tglx > Thanks, Alexey