On Mon, Jul 08, 2019 at 09:23:17AM +0800, Wei Wang wrote: > When the vCPU is scheduled in: > - if the lbr feature was used in the last vCPU time slice, set the lbr > stack to be interceptible, so that the host can capture whether the > lbr feature will be used in this time slice; > - if the lbr feature wasn't used in the last vCPU time slice, disable > the vCPU support of the guest lbr switching. > > Upon the first access to one of the lbr related MSRs (since the vCPU was > scheduled in): > - record that the guest has used the lbr; > - create a host perf event to help save/restore the guest lbr stack; > - pass the stack through to the guest. I don't understand a word of that. Who cares if the LBR MSRs are touched; the guest expects up-to-date values when it does reads them.
