linux-kernel - Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics event

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Date:   Sat, 30 Sep 2023 17:31:39 -0700
From:   Namhyung Kim <namhyung@...nel.org>
To:     Jim Mattson <jmattson@...gle.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dapeng Mi <dapeng1.mi@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Like Xu <likexu@...cent.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>,
        Adrian Hunter <adrian.hunter@...el.com>, kvm@...r.kernel.org,
        linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        Zhenyu Wang <zhenyuw@...ux.intel.com>,
        Zhang Xiong <xiong.y.zhang@...el.com>,
        Lv Zhiyuan <zhiyuan.lv@...el.com>,
        Yang Weijiang <weijiang.yang@...el.com>,
        Dapeng Mi <dapeng1.mi@...el.com>,
        David Dunn <daviddunn@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics event

Hello,

On Fri, Sep 29, 2023 at 8:29 PM Jim Mattson <jmattson@...gle.com> wrote:
> For things to work well in the "vPMU as a client of host perf" world,
> we need to have the following at a minimum:
> 1) Guaranteed identity mapping of guest PMCs to host PMCs, so that we
> don't have to intercept accesses to IA32_PERF_GLOBAL_CTRL.
> 2) Exclusive ownership of the PMU MSRs while in the KVM_RUN loop, so
> that we don't have to switch any PMU MSRs on VM-entry/VM-exit (with
> the exception of IA32_PERF_GLOBAL_CTRL, which has guest and host
> fields in the VMCS).

IIUC that means multiplexing should be handled in the guest.
Not sure it can support mixing host and guest events at the
same time.

Thanks,
Namhyung