Hi Marc, On 2021/4/15 18:42, Marc Zyngier wrote: > On Thu, 15 Apr 2021 07:59:26 +0100, > Keqian Zhu <zhukeqi...@huawei.com> wrote: >> >> Hi Marc, >> >> On 2021/4/14 21:44, Marc Zyngier wrote: >>> KVM/arm64 is the sole user of perf_num_counters(), and really >>> could do without it. Stop using the obsolete API by relying on >>> the existing probing code. >>> >>> Signed-off-by: Marc Zyngier <m...@kernel.org> >>> --- >>> arch/arm64/kvm/perf.c | 7 +------ >>> arch/arm64/kvm/pmu-emul.c | 2 +- >>> include/kvm/arm_pmu.h | 4 ++++ >>> 3 files changed, 6 insertions(+), 7 deletions(-) >>> >>> diff --git a/arch/arm64/kvm/perf.c b/arch/arm64/kvm/perf.c >>> index 739164324afe..b8b398670ef2 100644 >>> --- a/arch/arm64/kvm/perf.c >>> +++ b/arch/arm64/kvm/perf.c >>> @@ -50,12 +50,7 @@ static struct perf_guest_info_callbacks kvm_guest_cbs = { >>> >>> int kvm_perf_init(void) >>> { >>> - /* >>> - * Check if HW_PERF_EVENTS are supported by checking the number of >>> - * hardware performance counters. This could ensure the presence of >>> - * a physical PMU and CONFIG_PERF_EVENT is selected. >>> - */ >>> - if (IS_ENABLED(CONFIG_ARM_PMU) && perf_num_counters() > 0) >>> + if (kvm_pmu_probe_pmuver() != 0xf) >> The probe() function may be called many times >> (kvm_arm_pmu_v3_set_attr also calls it). I don't know whether the >> first calling is enough. If so, can we use a static variable in it, >> so the following calling can return the result right away? > > No, because that wouldn't help with crappy big-little implementations > that could have PMUs with different versions. We want to find the > version at the point where the virtual PMU is created, which is why we > call the probe function once per vcpu. I see.
But AFAICS the pmuver is placed in kvm->arch, and the probe function is called once per VM. Maybe I miss something. > > This of course is broken in other ways (BL+KVM is a total disaster > when it comes to PMU), but making this static would just make it > worse. OK. Thanks, Keqian _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm