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

[Jan Beulich <jbeulich@suse.com>]

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.)

Jan