Re: [PATCH v2 1/6] x86/cpu-policy: define bits of leaf 6

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 24/11/2025 12:23 pm, Jan Beulich wrote:
> ... as far as we presently use them in the codebase.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> Or should we make both parts proper featureset elements? At least
> APERFMPERF could likely be made visible to guests (in principle).
> ---
> v2: Use bool and unions.
>
> --- a/xen/include/xen/lib/x86/cpu-policy.h
> +++ b/xen/include/xen/lib/x86/cpu-policy.h
> @@ -121,7 +121,46 @@ struct cpu_policy
>              uint64_t :64, :64; /* Leaf 0x3 - PSN. */
>              uint64_t :64, :64; /* Leaf 0x4 - Structured Cache. */
>              uint64_t :64, :64; /* Leaf 0x5 - MONITOR. */
> -            uint64_t :64, :64; /* Leaf 0x6 - Therm/Perf. */
> +
> +            /* Leaf 0x6 - Therm/Perf. */
> +            union {
> +                uint32_t _6a;
> +                struct {
> +                    bool :1,
> +                        turbo:1,
> +                        arat:1,
> +                        :1,
> +                        :1,
> +                        :1,
> +                        :1,
> +                        hwp:1,
> +                        hwp_notification:1,
> +                        hwp_activity_window:1,
> +                        hwp_epp:1,
> +                        hwp_plr:1,
> +                        :1,
> +                        hdc:1,
> +                        :1,
> +                        :1,
> +                        hwp_peci:1,
> +                        :1,
> +                        :1,
> +                        hw_feedback:1;
> +                };
> +            };
> +            union {
> +                uint32_t _6b;
> +            };
> +            union {
> +                uint32_t _6c;
> +                struct {
> +                    bool aperfmperf:1;
> +                };
> +            };
> +            union {
> +                uint32_t _6d;
> +            };

The _6[a-d] variables are only needed for the featureset <-> policy
conversion which isn't the case here (notice how you don't need it the
series), and we're unlikely to want in the future.

This wants to read:

            /* Leaf 0x6 - Therm/Perf. */
            bool :1,
                turbo:1,
                arat:1,
                :1,
                :1,
                :1,
                :1,
                hwp:1,
                hwp_notification:1,
                hwp_activity_window:1,
                hwp_epp:1,
                hwp_plr:1,
                :1,
                hdc:1,
                :1,
                :1,
                hwp_peci:1,
                :1,
                :1,
                hw_feedback:1;
            uint32_t :32; /* b */
            bool aperfmperf:1;
            uint32_t :32; /* d */

and with that, Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>