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    SubjectRe: [PATCH RFC 2/2] KVM: x86/vPMU: ignore access to LBR-related MSRs
    On Wed, Dec 06, 2017 at 08:02:07PM +0300, Jan Dakinevich wrote:
    > On Wed, 6 Dec 2017 07:57:28 -0800
    > Andi Kleen <ak@linux.intel.com> wrote:
    >
    > >
    > > If you do all this it's only a small step to fully enable LBRs for
    > > guests.
    >
    > It is quite simple in a case where guest LBR-related MSRs matches host
    > ones. They could be handled by MSR load/store areas, I suppose.

    There is already a LBR control to enable/disable I believe.
    You don't want to save/restore all MSRs on every entry/exit
    because that would be slow. The normal Linux context switch can do it.

    >
    > In other cases, it could be expected the different amount of these MSRs
    > and different theirs base values (e.g. Nehalem vs Core). Guest MSRs
    > could be both subset and superset of host MSRs, so additional efforts
    > to support this would be required.

    In this case ignoring would be sufficient I suppose. But for the case
    when everything matches it should work.

    -Andi

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