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_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.
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
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 f99b0becd8..5d4439ba74 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3620,6 +3620,7 @@ static void kvm_accel_instance_init(Object *obj)
s->kvm_dirty_ring_size = 0;
s->notify_vmexit = NOTIFY_VMEXIT_OPTION_RUN;
s->notify_window = 0;
+ s->pmu_cap_disabled = false;
}
/**
diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
index 3b4adcdc10..e29ac5d767 100644
--- a/include/sysemu/kvm_int.h
+++ b/include/sysemu/kvm_int.h
@@ -110,6 +110,7 @@ struct KVMState
struct KVMDirtyRingReaper reaper;
NotifyVmexitOption notify_vmexit;
uint32_t notify_window;
+ bool pmu_cap_disabled;
};
void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
diff --git a/qemu-options.hx b/qemu-options.hx
index 7f99d15b23..15a2f717ff 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -186,6 +186,7 @@ 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[,...]]``
@@ -247,6 +248,12 @@ 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 a213209379..090e4fb44d 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -122,6 +122,7 @@ 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;
@@ -2652,6 +2653,23 @@ 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;
}
@@ -5706,6 +5724,28 @@ static void kvm_arch_set_notify_window(Object *obj, Visitor *v,
s->notify_window = 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",
@@ -5722,6 +5762,12 @@ void kvm_arch_accel_class_init(ObjectClass *oc)
object_class_property_set_description(oc, "notify-window",
"Clock cycles without an event window "
"after which a notification VM exit occurs");
+
+ 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
