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

Chen, Zide
2024-05-09T01:29:39Z

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.