On Tue, 2018-02-13 at 11:41 +0100, Paolo Bonzini wrote:

> On 13/02/2018 11:36, David Woodhouse wrote:
> > > > - if the VM has IBRS_ALL, pass through the MSR when it is zero and
> > > > intercept writes when it is one (no writes should happen)
> > > >  
> > > > - if the VM doesn't have IBRS_ALL, do as we are doing now, independent
> > > > of what the host spectre_v2_ibrs_all() setting is.
> > >
> > > We end up having to turn IBRS on again on vmexit then, taking care that
> > > no conditional branch can go round it. So that becomes an
> > > *unconditional* wrmsr or lfence in the vmexit path. We really don't
> > > want that.
> > >
> > Note that being able to keep it simple in KVM was basically what made
> > the difference between me tolerating IBRS_ALL as Intel currently define
> > it, and throwing my toys out of the pram (as I had done in the first
> > iterations of this patch).
> 
> You have my vote. :) 

I was taking that as assent to the patch... could I trouble you for an
explicit ack, please?