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From:   Namhyung Kim <namhyung@kernel.org>
Date:   Sat, 30 Sep 2023 17:31:39 -0700
Message-ID: <CAM9d7ciksqA7KGgc07HJAdE0TMpe1YCoS+NhzNEvdygh8T=PPA@mail.gmail.com>
Subject: Re: [Patch v4 07/13] perf/x86: Add constraint for guest perf metrics event
To:     Jim Mattson <jmattson@google.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dapeng Mi <dapeng1.mi@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Kan Liang <kan.liang@linux.intel.com>,
        Like Xu <likexu@tencent.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Jiri Olsa <jolsa@kernel.org>, Ian Rogers <irogers@google.com>,
        Adrian Hunter <adrian.hunter@intel.com>, kvm@vger.kernel.org,
        linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
        Zhenyu Wang <zhenyuw@linux.intel.com>,
        Zhang Xiong <xiong.y.zhang@intel.com>,
        Lv Zhiyuan <zhiyuan.lv@intel.com>,
        Yang Weijiang <weijiang.yang@intel.com>,
        Dapeng Mi <dapeng1.mi@intel.com>,
        David Dunn <daviddunn@google.com>,
        Mingwei Zhang <mizhang@google.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>
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Hello,

On Fri, Sep 29, 2023 at 8:29 PM Jim Mattson <jmattson@google.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