> This could achieve the above #1, but how would it solve #2 above? That is, > after the guest uses the lbr feature for a while, the lbr stack has been > passed through, then the guest doesn't use lbr any more, but the vCPU will > still save/restore on switching? If nothing accesses the MSR LBRs after a context switch in the guest nothing gets saved/restored due to: > > Also when the LBRs haven't been set to direct access the state doesn't > > need to be saved. -Andi
