On Thu, 28 Jan 2021 16:56:01 +0000 Marc Zyngier <maz@xxxxxxxxxx> wrote: > On 2021-01-28 15:16, Andre Przywara wrote: > > On Tue, 26 Jan 2021 15:15:20 +0000 > > Marc Zyngier <maz@xxxxxxxxxx> wrote: > > > > Hi Marc, > > > >> We currently find out about the presence of a HW PMU (or the handling > >> of that PMU by perf, which amounts to the same thing) in a fairly > >> roundabout way, by checking the number of counters available to perf. > >> That's good enough for now, but we will soon need to find about about > >> that on paths where perf is out of reach (in the world switch). > >> > >> Instead, let's turn kvm_arm_support_pmu_v3() into a static key. > > > > I am sure the pesky build bot has told you about it already, but this > > fails when ARM_PMU is not defined, as perf_num_counters() is not > > defined. It's bit nasty, since it's a generic function, so we > > can't easily stub it in its original header. > > No sign from the bot yet, but that's indeed a problem. Well spotted. > > > Shall we find a place somewhere in arch/arm64 and provide a stub > > implementation there, #ifndef CONFIG_ARM_PMU? Sounds ugly, though. > > > > Or something else entirely? > > How about: > > diff --git a/arch/arm64/kvm/perf.c b/arch/arm64/kvm/perf.c > index 198fa4266b2d..739164324afe 100644 > --- a/arch/arm64/kvm/perf.c > +++ b/arch/arm64/kvm/perf.c > @@ -55,7 +55,7 @@ int kvm_perf_init(void) > * hardware performance counters. This could ensure the presence of > * a physical PMU and CONFIG_PERF_EVENT is selected. > */ > - if (perf_num_counters() > 0) > + if (IS_ENABLED(CONFIG_ARM_PMU) && perf_num_counters() > 0) Neat! That indeed compiles and works in both cases (w/ and w/o ARM_PMU), fixing the original BUG I saw when using this as the L1 kernel. Thanks! Andre > static_branch_enable(&kvm_arm_pmu_available); > > return perf_register_guest_info_callbacks(&kvm_guest_cbs); > > It certainly compiles here. > > M. _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
