[PATCH 2/3] i386: kvm: disable KVM_CAP_PMU_CAPABILITY if "pmu" is disabled

[Dongli Zhang]

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@oracle.com>
Signed-off-by: Dongli Zhang <dongli.zhang@oracle.com>
---
 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);
+        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;
-- 
2.34.1