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From:   David Dunn <daviddunn@google.com>
Date:   Thu, 3 Feb 2022 09:33:49 -0800
Message-ID: <CABOYuvZJrBkcr5MCosVtq0+om5=kwcXWcFRNGxDyX_JPwpKubw@mail.gmail.com>
Subject: Re: [PATCH kvm/queue v2 2/3] perf: x86/core: Add interface to query
 perfmon_event_map[] directly
To:     Jim Mattson <jmattson@google.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        Like Xu <like.xu.linux@gmail.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Like Xu <likexu@tencent.com>,
        Stephane Eranian <eranian@google.com>
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Jim,

I agree.

It seems inevitable that the demands on the vPMU will continue to
grow.  On the current path, we will keep adding complexity to perf
until it essentially has a raw MSR interface used by KVM.

Your proposal gives a clean separation where KVM notifies perf when
the PMC will stop counting.  That handles both vPMU and TDX.  And it
allows KVM to provide the full expressiveness to guests.

Dave Dunn

On Wed, Feb 2, 2022 at 2:35 PM Jim Mattson <jmattson@google.com> wrote:

> Given what's coming with TDX, I wonder if we should just bite the
> bullet and cede the PMU to the guest while it's running, even for
> non-TDX guests. That would solve (1) and (2) as well.