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

Chen, Zide
2024-05-08T21:48:10Z

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?

> }
> break;