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@xxxxxxxxxxxxxxx> 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
