Re: [Xen-devel] [PATCH 2/2] x86/cpuid: Alter the policy logic for leaf 0xb to be multi-invocation

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 27/06/18 15:58, Jan Beulich wrote:
>>>> On 27.06.18 at 15:55, <andrew.cooper3@xxxxxxxxxx> wrote:
>> @@ -316,6 +319,33 @@ static void __init calculate_raw_policy(void)
>>              cpuid_count_leaf(7, i, &p->feat.raw[i]);
>>      }
>>  
>> +    if ( p->basic.max_leaf >= 0xb )
>> +    {
>> +        union {
>> +            struct cpuid_leaf l;
>> +            struct cpuid_topo_leaf t;
>> +        } u;
>> +
>> +        for ( i = 0; i < ARRAY_SIZE(p->topo.raw); ++i )
>> +        {
>> +            cpuid_count_leaf(0xb, i, &u.l);
>> +
>> +            if ( u.t.type == 0 )
>> +                break;
>> +
>> +            p->topo.subleaf[i] = u.t;
>> +        }
>> +
>> +        /*
>> +         * The choice of CPUID_GUEST_NR_TOPO is per the manual.  It may need
>> +         * to grow for future harware.
> Missing d.

Where?  I'm afraid that after repeated re-reads, I can't spot any issue.

>
>> @@ -108,7 +109,11 @@ struct cpuid_policy
>>              uint64_t :64, :64; /* Leaf 0x9 - DCA */
>>  
>>              /* Leaf 0xa - Intel PMU. */
>> -            uint8_t pmu_version;
>> +            uint8_t pmu_version, _pmu[15];
>> +
>> +            uint64_t :64, :64; /* Leaf 0xb - Topology. */
>> +            uint64_t :64, :64; /* Leaf 0xc - rsvd */
>> +            uint64_t :64, :64; /* Leaf 0xd - XSTATE. */
> I don't understand why you add the latter two lines, neither in general
> nor in the particular context of this patch.

This is part of reducing the effort for people extending the CPUID
leaves, by keeping the .basic union in line with max_leaf.

There are further non-subleaf leaves beyond this point (0x15/0x16) and
I've noticed several mistakes with newer submitted series.  I'd much
rather do this myself once now, than attempt to explain it to others
during code review.

~Andrew

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