Re: [PATCH v2 26/54] KVM: x86/pmu: Avoid legacy vPMU code when accessing global_ctrl in passthrough vPMU

Mi, Dapeng
2024-05-09T00:43:46Z

On 5/9/2024 5:48 AM, Chen, Zide wrote:
>
> On 5/5/2024 10:29 PM, Mingwei Zhang wrote:
>> Avoid calling into legacy/emulated vPMU logic such as reprogram_counters()
>> when passthrough vPMU is enabled. Note that even when passthrough vPMU is
>> enabled, global_ctrl may still be intercepted if guest VM only sees a
>> subset of the counters.
>>
>> Suggested-by: Xiong Zhang <xiong.y.zhang@linux.intel.com>
>> Signed-off-by: Mingwei Zhang <mizhang@google.com>
>> ---
>> arch/x86/kvm/pmu.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kvm/pmu.c b/arch/x86/kvm/pmu.c
>> index bd94f2d67f5c..e9047051489e 100644
>> --- a/arch/x86/kvm/pmu.c
>> +++ b/arch/x86/kvm/pmu.c
>> @@ -713,7 +713,8 @@ int kvm_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>> if (pmu->global_ctrl != data) {
>> diff = pmu->global_ctrl ^ data;
>> pmu->global_ctrl = data;
>> - reprogram_counters(pmu, diff);
>> + if (!is_passthrough_pmu_enabled(vcpu))
>> + reprogram_counters(pmu, diff);
> Since in [PATCH 44/54], reprogram_counters() is effectively skipped in
> the passthrough case, is this patch still needed?
Zide, reprogram_counters() and reprogram_counter() are two different
helpers. Both they need to be skipped in passthrough mode.
>
>> }
>> break;