Hi Like, On 7/2/23 06:41, Like Xu wrote: > On Wed, Jun 21, 2023 at 9:39 AM Dongli Zhang <dongli.zhang@xxxxxxxxxx> wrote: >> >> The "perf stat" at the VM side still works even we set "-cpu host,-pmu" in >> the QEMU command line. That is, neither "-cpu host,-pmu" nor "-cpu EPYC" >> could disable the pmu virtualization in an AMD environment. >> >> We still see below at VM kernel side ... >> >> [ 0.510611] Performance Events: Fam17h+ core perfctr, AMD PMU driver. >> >> ... although we expect something like below. >> >> [ 0.596381] Performance Events: PMU not available due to virtualization, using software events only. >> [ 0.600972] NMI watchdog: Perf NMI watchdog permanently disabled >> >> This is because the AMD pmu (v1) does not rely on cpuid to decide if the >> pmu virtualization is supported. >> >> We introduce a new property 'pmu-cap-disabled' for KVM accel to set >> KVM_PMU_CAP_DISABLE if KVM_CAP_PMU_CAPABILITY is supported. Only x86 host >> is supported because currently KVM uses KVM_CAP_PMU_CAPABILITY only for >> x86. > > We may check cpu->enable_pmu when creating the first CPU or a BSP one > (before it gets running) and then choose whether to disable guest pmu using > vm ioctl KVM_CAP_PMU_CAPABILITY. Introducing a new property is not too > acceptable if there are other options. In the v1 of the implementation, we have implemented something similar: not based on the cpu_index (or BSP), but to introduce a helper before creating the KVM vcpu to let the further implementation decide. We did the KVM_CAP_PMU_CAPABILITY in that helper once. [PATCH 1/3] kvm: introduce a helper before creating the 1st vcpu https://lore.kernel.org/all/20221119122901.2469-2-dongli.zhang@xxxxxxxxxx/ [PATCH 2/3] i386: kvm: disable KVM_CAP_PMU_CAPABILITY if "pmu" is disabled https://lore.kernel.org/all/20221119122901.2469-3-dongli.zhang@xxxxxxxxxx/ The below was the suggestion from Greg Kurz about to use per-VCPU property to control per-VM cap: "It doesn't seem conceptually correct to configure VM level stuff out of a vCPU property, which could theoretically be different for each vCPU, even if this isn't the case with the current code base. Maybe consider controlling PMU with a machine property and this could be done in kvm_arch_init() like other VM level stuff ?" Would you mind comment on that? Thank you very much! Dongli Zhang > >> >> Cc: Joe Jin <joe.jin@xxxxxxxxxx> >> Cc: Like Xu <likexu@xxxxxxxxxxx> >> Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx> >> --- >> Changed since v1: >> - In version 1 we did not introduce the new property. We ioctl >> KVM_PMU_CAP_DISABLE only before the creation of the 1st vcpu. We had >> introduced a helpfer function to do this job before creating the 1st >> KVM vcpu in v1. >> >> accel/kvm/kvm-all.c | 1 + >> include/sysemu/kvm_int.h | 1 + >> qemu-options.hx | 7 ++++++ >> target/i386/kvm/kvm.c | 46 ++++++++++++++++++++++++++++++++++++++++ >> 4 files changed, 55 insertions(+) >> >> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c >> index 7679f397ae..238098e991 100644 >> --- a/accel/kvm/kvm-all.c >> +++ b/accel/kvm/kvm-all.c >> @@ -3763,6 +3763,7 @@ static void kvm_accel_instance_init(Object *obj) >> s->xen_version = 0; >> s->xen_gnttab_max_frames = 64; >> s->xen_evtchn_max_pirq = 256; >> + s->pmu_cap_disabled = false; >> } >> >> /** >> diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h >> index 511b42bde5..cbbe08ec54 100644 >> --- a/include/sysemu/kvm_int.h >> +++ b/include/sysemu/kvm_int.h >> @@ -123,6 +123,7 @@ struct KVMState >> uint32_t xen_caps; >> uint16_t xen_gnttab_max_frames; >> uint16_t xen_evtchn_max_pirq; >> + bool pmu_cap_disabled; >> }; >> >> void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml, >> diff --git a/qemu-options.hx b/qemu-options.hx >> index b57489d7ca..1976c0ca3e 100644 >> --- a/qemu-options.hx >> +++ b/qemu-options.hx >> @@ -187,6 +187,7 @@ DEF("accel", HAS_ARG, QEMU_OPTION_accel, >> " tb-size=n (TCG translation block cache size)\n" >> " dirty-ring-size=n (KVM dirty ring GFN count, default 0)\n" >> " notify-vmexit=run|internal-error|disable,notify-window=n (enable notify VM exit and set notify window, x86 only)\n" >> + " pmu-cap-disabled=true|false (disable KVM_CAP_PMU_CAPABILITY, x86 only, default false)\n" >> " thread=single|multi (enable multi-threaded TCG)\n", QEMU_ARCH_ALL) >> SRST >> ``-accel name[,prop=value[,...]]`` >> @@ -254,6 +255,12 @@ SRST >> open up for a specified of time (i.e. notify-window). >> Default: notify-vmexit=run,notify-window=0. >> >> + ``pmu-cap-disabled=true|false`` >> + When the KVM accelerator is used, it controls whether to disable the >> + KVM_CAP_PMU_CAPABILITY via KVM_PMU_CAP_DISABLE. When disabled, the >> + PMU virtualization is disabled at the KVM module side. This is for >> + x86 host only. >> + >> ERST >> >> DEF("smp", HAS_ARG, QEMU_OPTION_smp, >> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c >> index de531842f6..bf4136fa1b 100644 >> --- a/target/i386/kvm/kvm.c >> +++ b/target/i386/kvm/kvm.c >> @@ -129,6 +129,7 @@ static bool has_msr_ucode_rev; >> static bool has_msr_vmx_procbased_ctls2; >> static bool has_msr_perf_capabs; >> static bool has_msr_pkrs; >> +static bool has_pmu_cap; >> >> static uint32_t has_architectural_pmu_version; >> static uint32_t num_architectural_pmu_gp_counters; >> @@ -2767,6 +2768,23 @@ int kvm_arch_init(MachineState *ms, KVMState *s) >> } >> } >> >> + has_pmu_cap = kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY); >> + >> + if (s->pmu_cap_disabled) { >> + if (has_pmu_cap) { >> + ret = kvm_vm_enable_cap(s, KVM_CAP_PMU_CAPABILITY, 0, >> + KVM_PMU_CAP_DISABLE); >> + if (ret < 0) { >> + s->pmu_cap_disabled = false; >> + error_report("kvm: Failed to disable pmu cap: %s", >> + strerror(-ret)); >> + } >> + } else { >> + s->pmu_cap_disabled = false; >> + error_report("kvm: KVM_CAP_PMU_CAPABILITY is not supported"); >> + } >> + } >> + >> return 0; >> } >> >> @@ -5951,6 +5969,28 @@ static void kvm_arch_set_xen_evtchn_max_pirq(Object *obj, Visitor *v, >> s->xen_evtchn_max_pirq = value; >> } >> >> +static void kvm_set_pmu_cap_disabled(Object *obj, Visitor *v, >> + const char *name, void *opaque, >> + Error **errp) >> +{ >> + KVMState *s = KVM_STATE(obj); >> + bool pmu_cap_disabled; >> + Error *error = NULL; >> + >> + if (s->fd != -1) { >> + error_setg(errp, "Cannot set properties after the accelerator has been initialized"); >> + return; >> + } >> + >> + visit_type_bool(v, name, &pmu_cap_disabled, &error); >> + if (error) { >> + error_propagate(errp, error); >> + return; >> + } >> + >> + s->pmu_cap_disabled = pmu_cap_disabled; >> +} >> + >> void kvm_arch_accel_class_init(ObjectClass *oc) >> { >> object_class_property_add_enum(oc, "notify-vmexit", "NotifyVMexitOption", >> @@ -5990,6 +6030,12 @@ void kvm_arch_accel_class_init(ObjectClass *oc) >> NULL, NULL); >> object_class_property_set_description(oc, "xen-evtchn-max-pirq", >> "Maximum number of Xen PIRQs"); >> + >> + object_class_property_add(oc, "pmu-cap-disabled", "bool", >> + NULL, kvm_set_pmu_cap_disabled, >> + NULL, NULL); >> + object_class_property_set_description(oc, "pmu-cap-disabled", >> + "Disable KVM_CAP_PMU_CAPABILITY"); >> } >> >> void kvm_set_max_apic_id(uint32_t max_apic_id) >> -- >> 2.34.1 >>
