Re: [Xen-devel] [PATCH v5 1/4] xen/libxc: Allow changes to hypervisor CPUID leaf from config file

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 03/19/2014 05:29 AM, Ian Campbell wrote:
> On Wed, 2014-03-19 at 09:26 +0000, Jan Beulich wrote:
> > > > > On 19.03.14 at 01:58, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > Currently only "real" cpuid leaves can be overwritten by users via
> > > 'cpuid' option in the configuration file. This patch provides ability to
> > > do the same for hypervisor leaves (but for now only 0x40000000 is allowed).
> > I'm still not really happy with the approach:
> >
> > > --- a/xen/arch/x86/traps.c
> > > +++ b/xen/arch/x86/traps.c
> > > @@ -690,6 +690,9 @@ int cpuid_hypervisor_leaves( uint32_t idx, uint32_t sub_idx,
> > >       if ( idx > limit )
> > >           return 0;
> > >   
> > > +    if ( domain_cpuid_exists(d, base + idx, sub_idx, eax, ebx, ecx, edx) )
> > > +        return 1;
> > You basically rely here on the tools having fed back the values the
> > hypervisor returned to them. What if this gets tweaked at some
> > point based on some other domain characteristics? I'd really like to
> > see the hypervisor, and only the hypervisor, being in charge of
> > returning the hypervisor leaf values. The sole restriction the tools
> > may place ought to be on the maximum leaf.
> That does sound like it would simplify things.

I'll move the enforcement of cpuid values to cpuid_hypervisor_leaves() 
then. It will also address (to some extent) the comment below.
-boris

> > Sadly I didn't see anyone else commenting on this model of yours,
> > so I can't judge whether I'm the only one having reservations
> > against the model you have been proposing so far.
> Well, the libxc side is certainly very complicated if all which is
> needed is the ability to limit the maximum hypervisor leaf which is
> exposed. That ought to be a dozen lines max across tools and hypervisor
> I would have said.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel