Re: [PATCH v3 03/13] libs/guest: allow fetching a specific MSR entry from a cpu policy

["Roger Pau Monné" <roger.pau@citrix.com>]

On Mon, May 03, 2021 at 12:41:29PM +0200, Jan Beulich wrote:
> On 30.04.2021 17:52, Roger Pau Monne wrote:
> > Introduce an interface that returns a specific MSR entry from a cpu
> > policy in xen_msr_entry_t format. Provide a helper to perform a binary
> > search against an array of MSR entries.
> > 
> > This is useful to callers can peek data from the opaque
> > xc_cpu_policy_t type.
> > 
> > No caller of the interface introduced on this patch.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> > ---
> > Changes since v1:
> >  - Introduce a helper to perform a binary search of the MSR entries
> >    array.
> > ---
> >  tools/include/xenctrl.h         |  2 ++
> >  tools/libs/guest/xg_cpuid_x86.c | 42 +++++++++++++++++++++++++++++++++
> >  2 files changed, 44 insertions(+)
> > 
> > diff --git a/tools/include/xenctrl.h b/tools/include/xenctrl.h
> > index cbca7209e34..605c632cf30 100644
> > --- a/tools/include/xenctrl.h
> > +++ b/tools/include/xenctrl.h
> > @@ -2611,6 +2611,8 @@ int xc_cpu_policy_serialise(xc_interface *xch, const xc_cpu_policy_t policy,
> >  int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t policy,
> >                              uint32_t leaf, uint32_t subleaf,
> >                              xen_cpuid_leaf_t *out);
> > +int xc_cpu_policy_get_msr(xc_interface *xch, const xc_cpu_policy_t policy,
> > +                          uint32_t msr, xen_msr_entry_t *out);
> >  
> >  int xc_get_cpu_levelling_caps(xc_interface *xch, uint32_t *caps);
> >  int xc_get_cpu_featureset(xc_interface *xch, uint32_t index,
> > diff --git a/tools/libs/guest/xg_cpuid_x86.c b/tools/libs/guest/xg_cpuid_x86.c
> > index de27826f415..9e83daca0e6 100644
> > --- a/tools/libs/guest/xg_cpuid_x86.c
> > +++ b/tools/libs/guest/xg_cpuid_x86.c
> > @@ -850,3 +850,45 @@ int xc_cpu_policy_get_cpuid(xc_interface *xch, const xc_cpu_policy_t policy,
> >      *out = *tmp;
> >      return 0;
> >  }
> > +
> > +static int compare_entries(const void *l, const void *r)
> > +{
> > +    const xen_msr_entry_t *lhs = l;
> > +    const xen_msr_entry_t *rhs = r;
> > +
> > +    if ( lhs->idx == rhs->idx )
> > +        return 0;
> > +    return lhs->idx < rhs->idx ? -1 : 1;
> > +}
> > +
> > +static xen_msr_entry_t *find_entry(xen_msr_entry_t *entries,
> > +                                   unsigned int nr_entries, unsigned int index)
> > +{
> > +    const xen_msr_entry_t key = { index };
> > +
> > +    return bsearch(&key, entries, nr_entries, sizeof(*entries), compare_entries);
> > +}
> 
> Isn't "entries" / "entry" a little too generic a name here, considering
> the CPUID equivalents use "leaves" / "leaf"? (Noticed really while looking
> at patch 7.)

Would you be fine with naming the function find_msr and leaving the
rest of the parameters names as-is?

Thanks, Roger.