@@ -130,6 +130,21 @@ config KVM_BOOK3S_HV_EXIT_TIMING
If unsure, say N.
+config KVM_BOOK3S_HV_NESTED_PMU_WORKAROUND
+ bool "Nested L0 host workaround for L1 KVM host PMU handling bug" if EXPERT
+ depends on KVM_BOOK3S_HV_POSSIBLE
+ default !EXPERT
+ help
+ Old nested HV capable Linux guests have a bug where they don't
+ reflect the PMU in-use status of their L2 guest to the L0 host
+ while the L2 PMU registers are live. This can result in loss
+ of L2 PMU register state, causing perf to not work correctly in
+ L2 guests.
+
+ Selecting this option for the L0 host implements a workaround for
+ those buggy L1s which saves the L2 state, at the cost of performance
+ in all nested-capable guest entry/exit.
+
config KVM_BOOKE_HV
bool
@@ -4047,8 +4047,14 @@ static int kvmhv_p9_guest_entry(struct kvm_vcpu *vcpu, u64 time_limit,
vcpu->arch.vpa.dirty = 1;
save_pmu = lp->pmcregs_in_use;
}
- /* Must save pmu if this guest is capable of running nested guests */
- save_pmu |= nesting_enabled(vcpu->kvm);
+ if (IS_ENABLED(CONFIG_KVM_BOOK3S_HV_NESTED_PMU_WORKAROUND)) {
+ /*
+ * Save pmu if this guest is capable of running nested guests.
+ * This is option is for old L1s that do not set their
+ * lppaca->pmcregs_in_use properly when entering their L2.
+ */
+ save_pmu |= nesting_enabled(vcpu->kvm);
+ }
kvmhv_save_guest_pmu(vcpu, save_pmu);
#ifdef CONFIG_PPC_PSERIES