Re: [PATCH 14/21] libs/guest: introduce helper to check cpu policy compatibility

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Mar 30, 2021 at 06:02:45PM +0200, Jan Beulich wrote:
> On 23.03.2021 10:58, Roger Pau Monne wrote:
> > --- a/tools/libs/guest/xg_cpuid_x86.c
> > +++ b/tools/libs/guest/xg_cpuid_x86.c
> > @@ -1098,3 +1098,20 @@ int xc_cpu_policy_update_msrs(xc_interface *xch, 
> > xc_cpu_policy_t policy,
> >      return rc;
> >  
> >  }
> > +
> > +bool xc_cpu_policy_is_compatible(xc_interface *xch, const xc_cpu_policy_t 
> > p1,
> > +                                 const xc_cpu_policy_t p2)
> > +{
> > +    struct cpu_policy_errors err;
> 
> Don't you need an initializer here for ...
> 
> > +    int rc = x86_cpu_policies_are_compatible(p1, p2, &err);
> > +
> > +    if ( !rc )
> > +        return true;
> > +
> > +    if ( err.leaf != -1 )
> > +        ERROR("Leaf %#x subleaf %#x is not compatible", err.leaf, 
> > err.subleaf);
> > +    if ( err.msr != -1 )
> > +        ERROR("MSR index %#x is not compatible", err.msr);
> 
> ... these checks to have a chance of actually triggering? (I'm also
> not certain -1 is a good indicator, but I guess we have been using it
> elsewhere as well.)

Well, this is strictly the error path, at which point I would expect
err to be properly set by x86_cpu_policies_are_compatible. I can
however initialize err for safety here.

Thanks, Roger.