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charset="utf-8" When PMU is enabled in QEMU, there is a chance that PMU virtualization is completely disabled by the KVM module parameter kvm.enable_pmu=3DN. The kvm.enable_pmu parameter is introduced since Linux v5.17. Its permission is 0444. It does not change until a reload of the KVM module. Read the kvm.enable_pmu value from the module sysfs to give a chance to provide more information about vPMU enablement. Signed-off-by: Dongli Zhang Reviewed-by: Zhao Liu Reviewed-by: Dapeng Mi --- Changed since v2: - Rework the code flow following Zhao's suggestion. - Return error when: (*kvm_enable_pmu =3D=3D 'N' && X86_CPU(cpu)->enable_pmu) Changed since v3: - Re-split the cases into enable_pmu and !enable_pmu, following Zhao's suggestion. - Rework the commit messages. - Bring back global static variable 'kvm_pmu_disabled' from v2. Changed since v4: - Add Reviewed-by from Zhao. Changed since v5: - Rebase on top of most recent QEMU. Changed since v6: - Add Reviewed-by from Dapeng Mi. target/i386/kvm/kvm.c | 61 +++++++++++++++++++++++++++++++------------ 1 file changed, 44 insertions(+), 17 deletions(-) diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c index 3b803c662d..338b9558e4 100644 --- a/target/i386/kvm/kvm.c +++ b/target/i386/kvm/kvm.c @@ -187,6 +187,10 @@ static int has_triple_fault_event; static bool has_msr_mcg_ext_ctl; =20 static int pmu_cap; +/* + * Read from /sys/module/kvm/parameters/enable_pmu. + */ +static bool kvm_pmu_disabled; =20 static struct kvm_cpuid2 *cpuid_cache; static struct kvm_cpuid2 *hv_cpuid_cache; @@ -2068,23 +2072,30 @@ int kvm_arch_pre_create_vcpu(CPUState *cpu, Error *= *errp) if (first) { first =3D false; =20 - /* - * 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 =3D 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 (X86_CPU(cpu)->enable_pmu) { + if (kvm_pmu_disabled) { + warn_report("Failed to enable PMU since " + "KVM's enable_pmu parameter is disabled"); + } + } else { + /* + * Since Linux v5.18, KVM provides a VM-level capability to ea= sily + * disable PMUs; however, QEMU has been providing PMU property= per + * CPU since v1.6. In order to accommodate both, have to confi= gure + * the VM-level capability here. + * + * KVM_PMU_CAP_DISABLE doesn't change the PMU + * behavior on Intel platform because current "pmu" property w= orks + * as expected. + */ + if (pmu_cap & KVM_PMU_CAP_DISABLE) { + ret =3D kvm_vm_enable_cap(kvm_state, KVM_CAP_PMU_CAPABILIT= Y, 0, + KVM_PMU_CAP_DISABLE); + if (ret < 0) { + error_setg_errno(errp, -ret, + "Failed to set KVM_PMU_CAP_DISABLE"); + return ret; + } } } } @@ -3302,6 +3313,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s) int ret; struct utsname utsname; Error *local_err =3D NULL; + g_autofree char *kvm_enable_pmu; =20 /* * Initialize confidential guest (SEV/TDX) context, if required @@ -3437,6 +3449,21 @@ int kvm_arch_init(MachineState *ms, KVMState *s) =20 pmu_cap =3D kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY); =20 + /* + * The enable_pmu parameter is introduced since Linux v5.17, + * give a chance to provide more information about vPMU + * enablement. + * + * The kvm.enable_pmu's permission is 0444. It does not change + * until a reload of the KVM module. + */ + if (g_file_get_contents("/sys/module/kvm/parameters/enable_pmu", + &kvm_enable_pmu, NULL, NULL)) { + if (*kvm_enable_pmu =3D=3D 'N') { + kvm_pmu_disabled =3D true; + } + } + return 0; } =20 --=20 2.39.3