On 2024-10-14 7:56 a.m., Peter Zijlstra wrote:
> On Thu, Aug 01, 2024 at 04:58:23AM +0000, Mingwei Zhang wrote:
>
>> @@ -5941,8 +5942,21 @@ void perf_put_mediated_pmu(void)
>> }
>> EXPORT_SYMBOL_GPL(perf_put_mediated_pmu);
>>
>> +static void perf_switch_interrupt(bool enter, u32 guest_lvtpc)
>> +{
>> + /* Mediated passthrough PMU should have PASSTHROUGH_VPMU cap. */
>> + if (!passthru_pmu)
>> + return;
>> +
>> + if (passthru_pmu->switch_interrupt &&
>> + try_module_get(passthru_pmu->module)) {
>> + passthru_pmu->switch_interrupt(enter, guest_lvtpc);
>> + module_put(passthru_pmu->module);
>> + }
>> +}
>
> Should we move the whole module reference to perf_pmu_(,un}register() ?
A PMU module can be load/unload anytime. How should we know if the PMU
module is available when the reference check is moved to
perf_pmu_(,un}register()?
>
>> @@ -11842,7 +11860,21 @@ int perf_pmu_register(struct pmu *pmu, const char *name, int type)
>> if (!pmu->event_idx)
>> pmu->event_idx = perf_event_idx_default;
>>
>> - list_add_rcu(&pmu->entry, &pmus);
>> + /*
>> + * Initialize passthru_pmu with the core pmu that has
>> + * PERF_PMU_CAP_PASSTHROUGH_VPMU capability.
>> + */
>> + if (pmu->capabilities & PERF_PMU_CAP_PASSTHROUGH_VPMU) {
>> + if (!passthru_pmu)
>> + passthru_pmu = pmu;
>> +
>> + if (WARN_ONCE(passthru_pmu != pmu, "Only one passthrough PMU is supported\n")) {
>> + ret = -EINVAL;
>> + goto free_dev;
>
> Why impose this limit? Changelog also fails to explain this.
Because the passthru_pmu is global variable. If there are two or more
PMUs with the PERF_PMU_CAP_PASSTHROUGH_VPMU, the former one will be
implicitly overwritten if without the check.
Thanks
Kan
>
>> + }
>> + }
>> +
>> + list_add_tail_rcu(&pmu->entry, &pmus);
>> atomic_set(&pmu->exclusive_cnt, 0);
>> ret = 0;
>> unlock:
>> --
>> 2.46.0.rc1.232.g9752f9e123-goog
>>
>
