On 2026/07/13 16:41, Oliver Upton wrote:
On Fri, Jul 10, 2026 at 08:15:03PM +0900, Akihiko Odaki wrote:@@ -813,6 +842,15 @@ void kvm_host_pmu_init(struct arm_pmu *pmu) if (!pmuv3_implemented(kvm_arm_pmu_get_pmuver_limit())) return;+ /*+ * IMPDEF PMUv3 traps are non-architectural, and KVM cannot assume a + * uniform PMUv3-compatible arm_pmu is available on all CPUs. + */ + if (cpus_have_final_cap(ARM64_WORKAROUND_PMUV3_IMPDEF_TRAPS)) { + kvm_info("Non-architectural PMU, tainting kernel\n"); + add_taint(TAINT_CPU_OUT_OF_SPEC, LOCKDEP_STILL_OK); + } +This is an unrelated change, and really the taint should be added with the .cpu_enable() for this capability. That's the point where we flip the magic bit.
I'm abandoning this change because it does not effectively cover all corner cases we don't want to support:
https://lore.kernel.org/all/[email protected]/
+void kvm_vcpu_load_pmu(struct kvm_vcpu *vcpu, int last_cpu) +{ + if (!kvm_pmu_fixed_counters_only(vcpu->kvm) || vcpu->cpu == last_cpu || last_cpu == -1)^~~~~~~~~~~~~~ Does this do anything other than avoid a spurious reload on the first KVM_RUN?
Yes. Without this check, the value will be passed to cpu_max_bits_warn() in the following call chain, resulting in a warning ifdef CONFIG_DEBUG_PER_CPU_MAPS:
1. kvm_vcpu_load_pmu() 2. kvm_pmu_probe_armpmu() 3. cpumask_test_cpu() 4. cpumask_check() 5. cpu_max_bits_warn() Regards, Akihiko Odaki
