Messages in this thread |  | | Date | Mon, 8 Dec 2025 12:51:56 +0100 | | From | Peter Zijlstra <> | | Subject | Re: [PATCH v6 04/44] perf: Add APIs to create/release mediated guest vPMUs |
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On Fri, Dec 05, 2025 at 04:16:40PM -0800, Sean Christopherson wrote:
> +static atomic_t nr_include_guest_events __read_mostly; > + > +static atomic_t nr_mediated_pmu_vms __read_mostly; > +static DEFINE_MUTEX(perf_mediated_pmu_mutex);
> +static int mediated_pmu_account_event(struct perf_event *event) > +{ > + if (!is_include_guest_event(event)) > + return 0; > + > + guard(mutex)(&perf_mediated_pmu_mutex); > + > + if (atomic_read(&nr_mediated_pmu_vms)) > + return -EOPNOTSUPP; > + > + atomic_inc(&nr_include_guest_events); > + return 0; > +} > + > +static void mediated_pmu_unaccount_event(struct perf_event *event) > +{ > + if (!is_include_guest_event(event)) > + return; > + > + atomic_dec(&nr_include_guest_events); > +}
> +int perf_create_mediated_pmu(void) > +{ > + guard(mutex)(&perf_mediated_pmu_mutex); > + if (atomic_inc_not_zero(&nr_mediated_pmu_vms)) > + return 0; > + > + if (atomic_read(&nr_include_guest_events)) > + return -EBUSY; > + > + atomic_inc(&nr_mediated_pmu_vms); > + return 0; > +} > +EXPORT_SYMBOL_GPL(perf_create_mediated_pmu); > + > +void perf_release_mediated_pmu(void) > +{ > + if (WARN_ON_ONCE(!atomic_read(&nr_mediated_pmu_vms))) > + return; > + > + atomic_dec(&nr_mediated_pmu_vms); > +} > +EXPORT_SYMBOL_GPL(perf_release_mediated_pmu);
These two things are supposed to be symmetric, but are implemented differently; what gives?
That is, should not both have the general shape:
if (atomic_inc_not_zero(&A)) return 0;
guard(mutex)(&lock);
if (atomic_read(&B)) return -EBUSY;
atomic_inc(&A); return 0;
Similarly, I would imagine both release variants to have the underflow warn on like:
if (WARN_ON_ONCE(!atomic_read(&A))) return;
atomic_dec(&A);
Hmm?
Also, EXPORT_SYMBOL_FOR_KVM() ?
I can make these edits when applying, if/when we get to applying. Let me continue reading.
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