Re: [PATCH 3/8] kvm: vmx: pass MSR_IA32_SPEC_CTRL and MSR_IA32_PRED_CMD down to the guest

[Paolo Bonzini]

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