On Fri, Jan 26, 2024, Xiong Zhang wrote: > + /* > + * When PMU is pass-through into guest, this handler should be forbidden from > + * running, the reasons are: > + * 1. After perf_guest_switch_to_kvm_pmi_vector() is called, and before cpu > + * enter into non-root mode, NMI could happen, but x86_pmu_handle_irq() > + * restore PMU to use NMI vector, which destroy KVM PMI vector setting. > + * 2. When VM is running, host NMI other than PMI causes VM exit, KVM will > + * call host NMI handler (vmx_vcpu_enter_exit()) first before KVM save > + * guest PMU context (kvm_pmu_save_pmu_context()), as x86_pmu_handle_irq() > + * clear global_status MSR which has guest status now, then this destroy > + * guest PMU status. > + * 3. After VM exit, but before KVM save guest PMU context, host NMI other > + * than PMI could happen, x86_pmu_handle_irq() clear global_status MSR > + * which has guest status now, then this destroy guest PMU status. > + */ > + if (perf_is_in_guest_passthrough()) Maybe a name more along the lines of: if (perf_is_guest_context_loaded()) because that makes it more obvious that the NMI _can't_ belong to the host PMU. For that matter, I would also rename __perf_force_exclude_guest to perf_guest_context_loaded (or "active" if that's better). The boolean tracks the state (guest vs. host context loaded/active), where as forcing perf events to exclude_guest is an action based on that state.
