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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 063AEC2D0DB for ; Mon, 20 Jan 2020 15:34:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CD43B21D7E for ; Mon, 20 Jan 2020 15:34:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728596AbgATPeB (ORCPT ); Mon, 20 Jan 2020 10:34:01 -0500 Received: from foss.arm.com ([217.140.110.172]:33770 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726642AbgATPeA (ORCPT ); Mon, 20 Jan 2020 10:34:00 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 1D06630E; Mon, 20 Jan 2020 07:34:00 -0800 (PST) Received: from lakrids.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5DBB83F52E; Mon, 20 Jan 2020 07:33:58 -0800 (PST) Date: Mon, 20 Jan 2020 15:33:56 +0000 From: Mark Rutland To: Peter Zijlstra Cc: James Clark , Will Deacon , "linux-arm-kernel@lists.infradead.org" , nd , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Jiri Olsa , Tan Xiaojun , Al Grant , Namhyung Kim , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH 1/1] Return EINVAL when precise_ip perf events are requested on Arm Message-ID: <20200120153355.GC43842@lakrids.cambridge.arm.com> References: <20200115105855.13395-1-james.clark@arm.com> <20200115105855.13395-2-james.clark@arm.com> <20200117123920.GB8199@willie-the-truck> <20200117140143.GD14879@hirez.programming.kicks-ass.net> <1231fd60-79cd-fcdf-8b99-a3be746bf2d1@arm.com> <20200117151658.GH14879@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200117151658.GH14879@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jan 17, 2020 at 04:16:58PM +0100, Peter Zijlstra wrote: > On Fri, Jan 17, 2020 at 03:00:37PM +0000, James Clark wrote: > > Hi Peter, > > > > Do you mean something like this? > > Yes. > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index 43d1d4945433..f74acd085bea 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -10812,6 +10812,12 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, > > goto err_pmu; > > } > > > > + if (event->attr.precise_ip && > > + !(pmu->capabilities & PERF_PMU_CAP_PRECISE_IP)) { > > + err = -EOPNOTSUPP; > > + goto err_pmu; > > + } > > + > > err = exclusive_event_init(event); > > if (err) > > goto err_pmu; > > > > > > Or should it only be done via sysfs to not break userspace? > > So we've added checks like this in the past and gotten away with it. Do > you already know of some userspace that will break due to it? > > An alternative approach is adding a sysctl like kernel.perf_nostrict > which would disable this or something, that way 'old' userspace has a > chicken bit. Could we allocate a "strict" bit from perf_event_attr::__reserved_1, and update drivers to expose a whitelist of fields they support? Then the core could do something like: if (attr->strict && !pmu_check_whitelist(pmu, attr)) return -EOPNOTSUPP; ... and we could also expose the whitelist somewhere in sysfs. Thanks, Mark,