linux-kernel - RE: [PATCH v1] KVM/x86/vPMU: Guest PMI Optimization

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Date:   Sun, 14 Oct 2018 13:42:24 +0000
From:   "Wang, Wei W" <wei.w.wang@...el.com>
To:     "Wang, Wei W" <wei.w.wang@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "Xu, Like" <like.xu@...el.com>
Subject: RE: [PATCH v1] KVM/x86/vPMU: Guest PMI Optimization

On Sunday, October 14, 2018 8:41 PM, Wei Wang wrote:
> Here is the plan I have in mind:
> #1 Creates a host perf event on the guest's first bit-setting to
> MSR_CORE_PERF_GLOBAL_CTRL; Meanwhile, disable the intercept of guest
> access to this perf counter related MSRs (i.e. config_base and event_base).
> #2 When the vCPU is sched in,
>      #2.1 make the MSRs of the perf counters (assigned to the guest in
> #1) interceptible, so that guest accesses to such a counter is captured, and
> marked it "used", and disable the intercept again;
>      #2.2 also check if there is any counter that wasn't "used" in the last vCPU
> time slice, if there is, release that counter and the perf event.

Just thought of an issue with passing through config_base and event base - the guest's view of the perf counter is possible to be different from the one assigned by the host, which results in guest using a different config_base and event_base. So we would still need keep those MSRs being intercepted by the host. The remaining part (the lazy allocation and release of the host perf event) can still work.

Best,
Wei