Re: [PATCH 2/8] x86/cpu-policy: define bits of leaf 6

[Jan Beulich <jbeulich@xxxxxxxx>]

On 18.11.2025 16:30, Andrew Cooper wrote:
> On 18/11/2025 3:06 pm, Jan Beulich wrote:
>> --- a/xen/include/xen/lib/x86/cpu-policy.h
>> +++ b/xen/include/xen/lib/x86/cpu-policy.h
>> @@ -121,7 +121,31 @@ 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. */
>> +            struct {
>> +                uint32_t /* a */:1,
>> +                    turbo:1,
>> +                    arat:1,
>> +                    :4,
>> +                    hwp:1,
>> +                    hwp_notification:1,
>> +                    hwp_activity_window:1,
>> +                    hwp_epp:1,
>> +                    hwp_plr:1,
>> +                    :1,
>> +                    hdc:1,
>> +                    :2,
>> +                    hwp_peci:1,
>> +                    :2,
>> +                    hw_feedback:1,
>> +                    :12;
>> +                uint32_t /* b */:32;
>> +                uint32_t /* c */ aperfmperf:1,
>> +                    :31;
>> +                uint32_t /* d */:32;
> 
> Elsewhere, single bit fields are bool foo:1, and these want to match for
> consistency.

Oh, yes, will change.

>  In particular using uint32_t:1 creates a latent bug in
> patch 8.

I don't see where that would be.

> One problem with bool bitfields is that your :4 needs to become 4x :1. 
> Right now his hidden in the macros that gen-cpuid.py makes.
> 
> Given that b is of type uint32_t, you can omit the :12 from the end of a
> and leave a comment.  Similarly, the trailing :31 on c can be dropped.

We have these in many other places, and omitting in particular the :31
would also feel somewhat fragile / misleading. It'll need to be

                bool     /* c */ aperfmperf:1;
                uint32_t :31;

or something along these lines.

>> +            } pm;
> 
> Nothing else is sub-scoped.  I'd prefer that you drop the 'pm'.

Wouldn't that require the use of the very extension you just talked about
at the committer's call?

Jan