Re: [Xen-devel] [PATCH RFC] pvh: clearly specify used parameters in vcpu_guest_context

[Tim Deegan <tim@xxxxxxx>]

At 16:32 +0000 on 15 Nov (1384529574), Jan Beulich wrote:
> >>> On 15.11.13 at 16:50, Roger Pau Monne <roger.pau@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/domain.c
> > +++ b/xen/arch/x86/domain.c
> > @@ -704,9 +704,11 @@ int arch_set_info_guest(
> >          /* PVH 32bitfixme */
> >          ASSERT(!compat);
> >  
> > -        if ( c(ctrlreg[1]) || c(ldt_base) || c(ldt_ents) ||
> > +        if ( c(ctrlreg[0]) || c(ctrlreg[1]) || c(ctrlreg[2]) ||
> > +             c(ctrlreg[4]) || c(ldt_base) || c(ldt_ents) ||
> 
> I think it should actually be a bug for the guest to request an
> all blank CR0 or CR4. Minimally CR0.PE, CR0.PG, and CR4.PAE
> would seem to be a valid requirement to be set.

I think zero is better.  Guest CRx are explicitly _not_ loaded from 
these fields so making them look like valid CRx values is just confusing.

But even better would be to allow all these fields to be set to any
valid values, and to load the state into the guest vCPU.  I think
that's going to be more sensible once the current restriction that PVH
vCPUs are always in long more goes away.

Tim.

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