On 27/02/2020 08:19, Jan Beulich wrote:
> On 26.02.2020 21:22, Andrew Cooper wrote:
>> For now, the default and max policies remain identical, but this will change
>> in the future. Write calculate_{pv,hvm}_def_policy() in a way which will
>> cope
>> with simple feature differences for now.
>>
>> Update XEN_SYSCTL_get_cpu_policy and init_domain_cpuid_policy() to use the
>> default policies.
> For the sysctl the statement looks to be broader than reality,
> as (of course) you don't touch XEN_SYSCTL_cpu_policy_*_max.
I'm afraid I don't understand what you mean here. What would I need to
touch in XEN_SYSCTL_cpu_policy_*_max at all?
>> @@ -381,6 +386,23 @@ static void __init calculate_pv_max_policy(void)
>> p->extd.raw[0xa] = EMPTY_LEAF; /* No SVM for PV guests. */
>> }
>>
>> +static void __init calculate_pv_def_policy(void)
>> +{
>> + struct cpuid_policy *p = &pv_def_cpuid_policy;
>> + uint32_t pv_featureset[FSCAPINTS];
>> + unsigned int i;
>> +
>> + *p = pv_max_cpuid_policy;
>> + cpuid_policy_to_featureset(p, pv_featureset);
>> +
>> + for ( i = 0; i < ARRAY_SIZE(pv_featureset); ++i )
>> + pv_featureset[i] &= pv_def_featuremask[i];
>> +
>> + sanitise_featureset(pv_featureset);
>> + cpuid_featureset_to_policy(pv_featureset, p);
>> + recalculate_xstate(p);
>> +}
> Is there a reason the call to guest_common_feature_adjustments()
> is missing here?
Yes, for the same reason that other logic is dropped. Inheriting from
pv_max_cpuid_policy means that it has already been run on this object.
The host to *_max derivation is non-trivial. Some features get added
in, others are conditional on external factors. The *_max to *_def
derivation is much more simple in comparison.
Long term, I expect this logic to move into libx86 and further simplify
cpuid.c
However, I'm not sure why guest_common_feature_adjustments() is special
compared to the other removed logic, and why it should be called out.
~Andrew
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