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Re: [PATCH RFC 2/2] KVM: x86/vPMU: ignore access to LBR-related MSRs

If you do all this it's only a small step to fully enable LBRs for guests. 

Just need to allow them to be written, expose PERF_CAPABILITIES too, and
start/stop them on entry/exit, and enable context switching through perf in
the host.

That would be far better than creating a frankenstate where LBR is there but
mostly broken on some KVM versions.