On 11/21/22 06:03, Greg Kurz wrote:
On Sat, 19 Nov 2022 04:29:00 -0800
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 disable KVM_CAP_PMU_CAPABILITY if the 'pmu' is disabled in the vcpu
properties.
Cc: Joe Jin <joe.jin@xxxxxxxxxx>
Signed-off-by: Dongli Zhang <dongli.zhang@xxxxxxxxxx>
---
target/i386/kvm/kvm.c | 17 +++++++++++++++++
1 file changed, 17 insertions(+)
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index 8fec0bc5b5..0b1226ff7f 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -137,6 +137,8 @@ static int has_triple_fault_event;
static bool has_msr_mcg_ext_ctl;
+static int has_pmu_cap;
+
static struct kvm_cpuid2 *cpuid_cache;
static struct kvm_cpuid2 *hv_cpuid_cache;
static struct kvm_msr_list *kvm_feature_msrs;
@@ -1725,6 +1727,19 @@ static void kvm_init_nested_state(CPUX86State *env)
void kvm_arch_pre_create_vcpu(CPUState *cs)
{
+ X86CPU *cpu = X86_CPU(cs);
+ int ret;
+
+ if (has_pmu_cap && !cpu->enable_pmu) {
+ ret = kvm_vm_enable_cap(kvm_state, KVM_CAP_PMU_CAPABILITY, 0,
+ KVM_PMU_CAP_DISABLE);
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 ?
There is already a 'pmu' property for x86_cpu with variable 'enable_pmu'
as we see the above code. It is mainly used by Intel CPU and set to off
by default since qemu 1.5.
And, this property is spread to AMD CPU too.
I think you may need setup a machine property to disable it from current
machine model. Otherwise, it will break the Live Migration scenario.
+ if (ret < 0) {
+ error_report("kvm: Failed to disable pmu cap: %s",
+ strerror(-ret));
+ }
+
+ has_pmu_cap = 0;
+ }
}
int kvm_arch_init_vcpu(CPUState *cs)
@@ -2517,6 +2532,8 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
}
}
+ has_pmu_cap = kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY);
+
ret = kvm_get_supported_msrs(s);
if (ret < 0) {
return ret;
