Re: [RFC PATCH 06/41] perf: x86: Add function to switch PMI handler

[Zhang, Xiong Y]

On 4/12/2024 3:17 AM, Sean Christopherson wrote:
> On Fri, Jan 26, 2024, Xiong Zhang wrote:
>> From: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
>>
>> Add function to switch PMI handler since passthrough PMU and host PMU will
>> use different interrupt vectors.
>>
>> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
>> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
>> ---
>>  arch/x86/events/core.c            | 15 +++++++++++++++
>>  arch/x86/include/asm/perf_event.h |  3 +++
>>  2 files changed, 18 insertions(+)
>>
>> diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
>> index 40ad1425ffa2..3f87894d8c8e 100644
>> --- a/arch/x86/events/core.c
>> +++ b/arch/x86/events/core.c
>> @@ -701,6 +701,21 @@ struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr, void *data)
>>  }
>>  EXPORT_SYMBOL_GPL(perf_guest_get_msrs);
>>  
>> +void perf_guest_switch_to_host_pmi_vector(void)
>> +{
>> +	lockdep_assert_irqs_disabled();
>> +
>> +	apic_write(APIC_LVTPC, APIC_DM_NMI);
>> +}
>> +EXPORT_SYMBOL_GPL(perf_guest_switch_to_host_pmi_vector);
>> +
>> +void perf_guest_switch_to_kvm_pmi_vector(void)
>> +{
>> +	lockdep_assert_irqs_disabled();
>> +
>> +	apic_write(APIC_LVTPC, APIC_DM_FIXED | KVM_VPMU_VECTOR);
>> +}
>> +EXPORT_SYMBOL_GPL(perf_guest_switch_to_kvm_pmi_vector);
> 
> Why slice and dice the context switch if it's all in perf?  Just do this in
> perf_guest_enter().  
> 
As perf_guest_enter() is in perf core which manages all PMUs, while switch_pmi_vector is for x86 core PMU only, so switch_pmi_vector is put in x86 pmu driver. pmu driver can call perf core function directly, perf core manage pmu through pmu->ops and pmu->flags. If switch_pmi_vector is called in perf_guest_enter, extra interfaces will be added into pmu->ops, this impacts other PMU driver.