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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 E9FD9C0044C for ; Wed, 31 Oct 2018 10:43:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AE78520838 for ; Wed, 31 Oct 2018 10:43:54 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AE78520838 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728626AbeJaTl0 (ORCPT ); Wed, 31 Oct 2018 15:41:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45124 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727852AbeJaTlZ (ORCPT ); Wed, 31 Oct 2018 15:41:25 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4A4E281DEA; Wed, 31 Oct 2018 10:43:51 +0000 (UTC) Received: from [10.36.112.62] (ovpn-112-62.ams2.redhat.com [10.36.112.62]) by smtp.corp.redhat.com (Postfix) with ESMTPS id E5D9D508E1; Wed, 31 Oct 2018 10:43:41 +0000 (UTC) Subject: Re: [PATCH v13 08/12] KVM: x86: Add Intel PT context switch for each vcpu To: Thomas Gleixner Cc: Alexander Shishkin , Luwei Kang , kvm@vger.kernel.org, x86@kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, rkrcmar@redhat.com, joro@8bytes.org, songliubraving@fb.com, peterz@infradead.org, kstewart@linuxfoundation.org, gregkh@linuxfoundation.org, thomas.lendacky@amd.com, konrad.wilk@oracle.com, mattst88@gmail.com, Janakarajan.Natarajan@amd.com, dwmw@amazon.co.uk, jpoimboe@redhat.com, marcorr@google.com, ubizjak@gmail.com, sean.j.christopherson@intel.com, jmattson@google.com, linux-kernel@vger.kernel.org, Chao Peng References: <1540368316-12998-1-git-send-email-luwei.kang@intel.com> <1540368316-12998-9-git-send-email-luwei.kang@intel.com> <87a7n37iuf.fsf@ashishki-desk.ger.corp.intel.com> From: Paolo Bonzini Openpgp: preference=signencrypt Autocrypt: addr=pbonzini@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Wed, 31 Oct 2018 10:43:51 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/10/2018 11:00, Thomas Gleixner wrote: > On Mon, 29 Oct 2018, Paolo Bonzini wrote: >> On 24/10/2018 12:13, Alexander Shishkin wrote: >>> Luwei Kang writes: >>>> + /* >>>> + * Set guest state of MSR_IA32_RTIT_CTL MSR (PT will be disabled >>>> + * on VM entry when it has been disabled in guest before). >>>> + */ >>>> + vmcs_write64(GUEST_IA32_RTIT_CTL, vmx->pt_desc.guest.ctl); >>>> + >>>> + if (vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) { >>>> + wrmsrl(MSR_IA32_RTIT_CTL, 0); >>>> + pt_save_msr(&vmx->pt_desc.host, vmx->pt_desc.addr_range); >>>> + pt_load_msr(&vmx->pt_desc.guest, vmx->pt_desc.addr_range); >>>> + } >>>> +} >>> >>> From my side this is still a NAK, because [1]. >>> >>> [1] https://marc.info/?l=kvm&m=153847567226248&w=2 >> >> Then you should have replied to >> https://marc.info/?l=kvm&m=153865386015249&w=2 instead of having Luwei >> do the work for nothing. >> >> Quoting from there: >> >>>> One shouldn't have to enable or disable anything in KVM to stop it from >>>> breaking one's existing workflow. That makes no sense. >>> >>> If you "have to enable or disable anything" it means you have to >>> override the default. But the default in this patches is "no change >>> compared to before the patches", leaving tracing of both host and guest >>> entirely to the host, so I don't understand your remark. What workflow >>> is broken? >>> >>>> There already are controls in perf that enable/disable guest tracing. >>> >>> You are confusing "tracing guest from the host" and "the guest can trace >>> itself". This patchset is adding support for the latter, and that >>> affects directly whether the tracing CPUID leaf can be added to the >>> guest. Therefore it's not perf that can decide whether to turn it on; >>> KVM must know it when /dev/kvm is opened, which is why it is a module >>> parameter. >> >> I'd be happier if we found an agreement, but without discussion that >> just won't happen. > > So at least we need a way for perf on the host to programmatically detect, > that 'guest traces itself' is enabled, so it can inject that information > into the host data and post processing can tell that. W/o something like > that it's going to be a FAQ. In guest-tracing mode there will be already a TIP.PGD and TIP.PGE packet respectively before vmentry and after vmexit, caused by the RTIT_CTL WRMSRs in pt_guest_enter and pt_guest_exit. The target IP of the packets will come from kvm-intel.ko. In system mode instead you get a Paging Information Packet on vmentry/vmexit, with bit 0 set in the third byte. You won't get it if guest-side tracing is on (because tracing has been disabled by pt_guest_enter and won't be re-enabled until pt_guest_exit). I don't think it's correct to "fake" the PIP in guest-tracing mode, because TIP.PGD should be followed immediately by TIP.PGE. Is this okay for perf users? Paolo