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=-10.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, NICE_REPLY_A,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 B821CC433E7 for ; Fri, 16 Oct 2020 11:38:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 5923020866 for ; Fri, 16 Oct 2020 11:38:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406361AbgJPLiw (ORCPT ); Fri, 16 Oct 2020 07:38:52 -0400 Received: from foss.arm.com ([217.140.110.172]:35278 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404884AbgJPLiw (ORCPT ); Fri, 16 Oct 2020 07:38:52 -0400 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 BEBBDD6E; Fri, 16 Oct 2020 04:38:51 -0700 (PDT) Received: from [10.57.50.28] (unknown [10.57.50.28]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 972553F719; Fri, 16 Oct 2020 04:38:49 -0700 (PDT) Subject: Re: [PATCH] coresight: etm4x: Add config to exclude kernel mode tracing To: Leo Yan , Sai Prakash Ranjan Cc: Denis Nikitin , Mathieu Poirier , linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org, linux-kernel@vger.kernel.org, Stephen Boyd , linux-arm-kernel@lists.infradead.org, Mike Leach References: <20201015124522.1876-1-saiprakash.ranjan@codeaurora.org> <20201015160257.GA1450102@xps15> <20201016072401.GC4646@leoy-ThinkPad-X240s> <20201016092450.GG4646@leoy-ThinkPad-X240s> From: Suzuki Poulose Message-ID: Date: Fri, 16 Oct 2020 12:38:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201016092450.GG4646@leoy-ThinkPad-X240s> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On 10/16/20 10:24 AM, Leo Yan wrote: > Hi Sai, > > On Fri, Oct 16, 2020 at 02:10:47PM +0530, Sai Prakash Ranjan wrote: >> Hi Leo, >> >> On 2020-10-16 12:54, Leo Yan wrote: >>> On Thu, Oct 15, 2020 at 11:40:05PM -0700, Denis Nikitin wrote: >>>> Hi Mathieu, >>>> >>>> I think one of the use cases could be VMs. >>>> Is there isolation between EL1 guest kernels which we can control >>>> from perf >>>> in a system wide mode? >>> >>> Sorry for suddenly jumping in. >>> >>> For KVM, I think we need to implement mechanism for saving/restoring >>> CoreSight context for every guest OS, the CPU PMUs has implemented >>> related features [1]. >>> >>> Thanks, >>> Leo >>> >>> [1] >>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm64/kvm/pmu.c >>> Its not as easy as the CPU PMU for virtualizing the ETMs (with memory mapped access only), i.e supporting ETMs from VMs. We could definitely stop/resume on guest entry/exit, to support attr.exclude_guest. >> >> What happens to the sysfs mode of tracing? For that we would still >> need a config right to exclude kernel mode tracing completely. > > IIUC, sysfs mode and perf mode both can apply the same approach, the > guest OS runs a thread context for the host, so when a guest OS is > switched in or out, the hypervisor can save/restore the context for > the guest OS; thus every guest OS will have its dedicated context and > trace data ideally. I don't think Guest Context is something we can support as mentioned above, at least for systems without sysreg access for ETMs (and virtualizing ETRs is a different story !) Cheers Suzuki