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.zhang@oracle.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
> ---
> Changed since v1:
> - Switch back to the initial implementation with "-pmu".
> https://lore.kernel.org/all/20221119122901.2469-3-dongli.zhang@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.mi@linux.intel.com>