Re: [RFC PATCH 05/41] KVM: x86/pmu: Register PMI handler for passthrough PMU

[Zhang, Xiong Y]

On 4/12/2024 3:07 AM, Sean Christopherson wrote:
> On Fri, Jan 26, 2024, Xiong Zhang wrote:
>> From: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
>>
>> Add function to register/unregister PMI handler at KVM module
>> initialization and destroy time. This allows the host PMU with passthough
>> capability enabled switch PMI handler at PMU context switch time.
>>
>> Signed-off-by: Xiong Zhang <xiong.y.zhang@xxxxxxxxx>
>> Signed-off-by: Mingwei Zhang <mizhang@xxxxxxxxxx>
>> ---
>>  arch/x86/kvm/x86.c | 14 ++++++++++++++
>>  1 file changed, 14 insertions(+)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 2c924075f6f1..4432e736129f 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -10611,6 +10611,18 @@ void __kvm_request_immediate_exit(struct kvm_vcpu *vcpu)
>>  }
>>  EXPORT_SYMBOL_GPL(__kvm_request_immediate_exit);
>>  
>> +void kvm_passthrough_pmu_handler(void)
> 
> s/pmu/pmi, and this needs a verb.  Maybe kvm_handle_guest_pmi()?  Definitely
> open to other names.
kvm_handle_guest_pmi() is ok. 
> 
>> +{
>> +	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
>> +
>> +	if (!vcpu) {
>> +		pr_warn_once("%s: no running vcpu found!\n", __func__);
> 
> Unless I misunderstand the code, this can/should be a full WARN_ON_ONCE.  If a
> PMI skids all the way past vcpu_put(), we've got big problems.
yes, it is big problems and user should be noticed.
>  
>> +		return;
>> +	}
>> +
>> +	kvm_make_request(KVM_REQ_PMI, vcpu);
>> +}
>> +
>>  /*
>>   * Called within kvm->srcu read side.
>>   * Returns 1 to let vcpu_run() continue the guest execution loop without
>> @@ -13815,6 +13827,7 @@ static int __init kvm_x86_init(void)
>>  {
>>  	kvm_mmu_x86_module_init();
>>  	mitigate_smt_rsb &= boot_cpu_has_bug(X86_BUG_SMT_RSB) && cpu_smt_possible();
>> +	kvm_set_vpmu_handler(kvm_passthrough_pmu_handler);
> 
> Hmm, a few patches late, but the "kvm" scope is weird.  This calls a core x86
> function, not a KVM function.
> 
> And to reduce exports and copy+paste, what about something like this?
> 
> void x86_set_kvm_irq_handler(u8 vector, void (*handler)(void))
> {
> 	if (!handler)
> 		handler = dummy_handler;
> 
> 	if (vector == POSTED_INTR_WAKEUP_VECTOR)
> 		kvm_posted_intr_wakeup_handler = handler;
> 	else if (vector == KVM_GUEST_PMI_VECTOR)
> 		kvm_guest_pmi_handler = handler;
> 	else
> 		WARN_ON_ONCE(1);
> 
> 	if (handler == dummy_handler)
> 		synchronize_rcu();
> }
> EXPORT_SYMBOL_GPL(x86_set_kvm_irq_handler);
Good suggestion. Follow it in next version.