On 6/24/2025 3:43 PM, Dongli Zhang wrote: > Although AMD PERFCORE and PerfMonV2 are removed when "-pmu" is configured, > there is no way to fully disable KVM AMD PMU virtualization. Neither > "-cpu host,-pmu" nor "-cpu EPYC" achieves this. > > As a result, the following message still appears in the VM dmesg: > > [ 0.263615] Performance Events: AMD PMU driver. > > However, the expected output should be: > > [ 0.596381] Performance Events: PMU not available due to virtualization, > using software events only. > [ 0.600972] NMI watchdog: Perf NMI watchdog permanently disabled > > This occurs because AMD does not use any CPUID bit to indicate PMU > availability. > > To address this, KVM_CAP_PMU_CAPABILITY is used to set KVM_PMU_CAP_DISABLE > when "-pmu" is configured. > > Signed-off-by: Dongli Zhang <dongli.zh...@oracle.com> > Reviewed-by: Xiaoyao Li <xiaoyao...@intel.com> > Reviewed-by: Zhao Liu <zhao1....@intel.com> > --- > Changed since v1: > - Switch back to the initial implementation with "-pmu". > https://lore.kernel.org/all/20221119122901.2469-3-dongli.zh...@oracle.com > - Mention that "KVM_PMU_CAP_DISABLE doesn't change the PMU behavior on > Intel platform because current "pmu" property works as expected." > Changed since v2: > - Change has_pmu_cap to pmu_cap. > - Use (pmu_cap & KVM_PMU_CAP_DISABLE) instead of only pmu_cap in if > statement. > - Add Reviewed-by from Xiaoyao and Zhao as the change is minor. > Changed since v5: > - Re-base on top of most recent mainline QEMU. > - To resolve conflicts, move the PMU related code before the > call site of is_tdx_vm(). > > target/i386/kvm/kvm.c | 31 +++++++++++++++++++++++++++++++ > 1 file changed, 31 insertions(+) > > diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c > index 234878c613..15155b79b5 100644 > --- a/target/i386/kvm/kvm.c > +++ b/target/i386/kvm/kvm.c > @@ -178,6 +178,8 @@ static int has_triple_fault_event; > > static bool has_msr_mcg_ext_ctl; > > +static int pmu_cap; > + > static struct kvm_cpuid2 *cpuid_cache; > static struct kvm_cpuid2 *hv_cpuid_cache; > static struct kvm_msr_list *kvm_feature_msrs; > @@ -2062,6 +2064,33 @@ full: > > int kvm_arch_pre_create_vcpu(CPUState *cpu, Error **errp) > { > + static bool first = true; > + int ret; > + > + if (first) { > + first = false; > + > + /* > + * Since Linux v5.18, KVM provides a VM-level capability to easily > + * disable PMUs; however, QEMU has been providing PMU property per > + * CPU since v1.6. In order to accommodate both, have to configure > + * the VM-level capability here. > + * > + * KVM_PMU_CAP_DISABLE doesn't change the PMU > + * behavior on Intel platform because current "pmu" property works > + * as expected. > + */ > + if ((pmu_cap & KVM_PMU_CAP_DISABLE) && !X86_CPU(cpu)->enable_pmu) { > + ret = kvm_vm_enable_cap(kvm_state, KVM_CAP_PMU_CAPABILITY, 0, > + KVM_PMU_CAP_DISABLE); > + if (ret < 0) { > + error_setg_errno(errp, -ret, > + "Failed to set KVM_PMU_CAP_DISABLE"); > + return ret; > + } > + } > + } > + > if (is_tdx_vm()) { > return tdx_pre_create_vcpu(cpu, errp); > } > @@ -3363,6 +3392,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s) > } > } > > + pmu_cap = kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY); > + > return 0; > } >
LGTM. Reviewed-by: Dapeng Mi <dapeng1...@linux.intel.com>
