Messages in this thread | | | Date | Wed, 6 Dec 2017 09:55:43 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH RFC 2/2] KVM: x86/vPMU: ignore access to LBR-related MSRs |
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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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