On 10/01/2018 16:48, Woodhouse, David wrote: >> >> And what is the point of this "always set IBRS=1" then? Are there >> some other things lurking in the shadows? > Yes. *FUTURE* CPUs will have a mode where you can just set IBRS and > leave it set for ever and not worry about any of this, and the > performance won't even suck. > > Quite why it's still an option you have to set in an MSR, and not just > a feature bit that they advertise and do it unconditionally, I have no > idea. But apparently that's the plan.
And again---why you still need IBPBs. That also escapes me. I wouldn't be surprised if that's just a trick to sneak it in a generation earlier... Paolo
