Re: [Xen-devel] [PATCH] x86/vPMU: constrain MSR_IA32_DS_AREA loads

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 12/17/2015 09:29 AM, Jan Beulich wrote:
> > > > On 17.12.15 at 15:26, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 12/17/2015 09:18 AM, Jan Beulich wrote:
> > > > > > On 17.12.15 at 15:12, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > > On 12/17/2015 09:01 AM, Jan Beulich wrote:
> > > > > @@ -415,8 +416,10 @@ static int core2_vpmu_verify(struct vcpu
> > > > >                 enabled_cntrs |= (1ULL << i);
> > > > >         }
> > > > >     
> > > > > -    if ( vpmu_is_set(vcpu_vpmu(v), VPMU_CPU_HAS_DS) &&
> > > > > -         !is_canonical_address(core2_vpmu_cxt->ds_area) )
> > > > > +    if ( vpmu_is_set(vpmu, VPMU_CPU_HAS_DS) &&
> > > > > +         !(has_hvm_container_vcpu(v)
> > > > > +           ? is_canonical_address(core2_vpmu_cxt->ds_area)
> > > > > +           : __addr_ok(core2_vpmu_cxt->ds_area)) )
> > > > Should we instead of (or in addition to) this also make the same change
> > > > in core2_vpmu_do_wrmsr()?
> > > Currently there's no need for this since - afaict - PV guests can't
> > > write this MSR directly (it's not among the white listed set in
> > > traps.c).
> > Then we probably shouldn't set VPMU_CPU_HAS_DS for PV guests.
> Or add the MSR to the permitted set. You know better than I
> what the best route here is.
I vaguely recall a conversation where we weren't sure whether BTS (which 
needs DS area) will work for PV. Something to do with DS address being 
in the right context (guest or host). I'd need to find that conversation 
(or test BTS on PV).
-boris


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