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

Mi, Dapeng
2024-05-09T02:58:31Z

On 5/9/2024 9:29 AM, Chen, Zide wrote:
>
> On 5/8/2024 5:43 PM, Mi, Dapeng wrote:
>> 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.
> Yes, but this is talking about reprogram_counters() only. passthrough
> mode is being checked inside and outside the function call, which is
> redundant.
Oh, yes. I don't need this patch then.