Re: [PATCH v2 36/54] KVM: x86/pmu: Switch PMI handler at KVM context switch boundary

Sandipan Das
2024-07-10T12:30:56Z

On 7/10/2024 3:31 PM, Zhang, Xiong Y wrote:
>
>> On 5/6/2024 11:00 AM, Mingwei Zhang wrote:
>>> From: Xiong Zhang <xiong.y.zhang@linux.intel.com>
>>>
>>> Switch PMI handler at KVM context switch boundary because KVM uses a
>>> separate maskable interrupt vector other than the NMI handler for the
>>> host PMU to process its own PMIs. So invoke the perf API that allows
>>> registration of the PMI handler.
>>>
>>> Signed-off-by: Xiong Zhang <xiong.y.zhang@linux.intel.com>
>>> Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
>>> ---
>>> arch/x86/kvm/pmu.c | 4 ++++
>>> 1 file changed, 4 insertions(+)
>>>
>>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c index
>>> 2ad71020a2c0..a12012a00c11 100644
>>> --- a/arch/x86/kvm/pmu.c
>>> +++ b/arch/x86/kvm/pmu.c
>>> @@ -1097,6 +1097,8 @@ void kvm_pmu_save_pmu_context(struct kvm_vcpu
>> *vcpu)
>>> if (pmc->counter)
>>> wrmsrl(pmc->msr_counter, 0);
>>> }
>>> +
>>> + x86_perf_guest_exit();
>>> }
>>>
>>> void kvm_pmu_restore_pmu_context(struct kvm_vcpu *vcpu) @@ -1107,6
>>> +1109,8 @@ void kvm_pmu_restore_pmu_context(struct kvm_vcpu *vcpu)
>>>
>>> lockdep_assert_irqs_disabled();
>>>
>>> + x86_perf_guest_enter(kvm_lapic_get_reg(vcpu->arch.apic,
>>> +APIC_LVTPC));
>>> +
>>
>> Reading the LVTPC for a vCPU that does not have a struct kvm_lapic allocated
>> leads to a NULL pointer dereference. I noticed this while trying to run a
>> minimalistic guest like https://github.com/dpw/kvm-hello-world
>>
>> Does this require a kvm_lapic_enabled() or similar check?
>>
>
> Intel processor has lapci_in_kernel() checking in "[RFC PATCH v3 16/54] KVM: x86/pmu: Plumb through pass-through PMU to vcpu for Intel CPUs".
> + pmu->passthrough = vcpu->kvm->arch.enable_passthrough_pmu &&
> + lapic_in_kernel(vcpu);
>
> AMD processor seems need this checking also. we could move this checking into common place.
>

Thanks. Adding that fixes the issue.

>
>>> static_call_cond(kvm_x86_pmu_restore_pmu_context)(vcpu);
>>>
>>> /*
>