[v2,07/10] target/i386/kvm: query kvm.enable_pmu parameter

Commit Message

Dongli Zhang March 2, 2025, 10 p.m. UTC

There is no way to distinguish between the following scenarios:

(1) KVM_CAP_PMU_CAPABILITY is not supported.
(2) KVM_CAP_PMU_CAPABILITY is supported but disabled via the module
parameter kvm.enable_pmu=N.

In scenario (1), there is no way to fully disable AMD PMU virtualization.

In scenario (2), PMU virtualization is completely disabled by the KVM
module.

To help determine the scenario, read the kvm.enable_pmu value from the
sysfs module parameter.

There isn't any requirement to initialize 'has_pmu_version',
'num_pmu_gp_counters' or 'num_pmu_fixed_counters', if kvm.enable_pmu=N.

Signed-off-by: Dongli Zhang <[e-mail]>
---
 target/i386/kvm/kvm.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

Patch

diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index e895d22f94..efba3ae7a4 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -184,6 +184,10 @@  static int has_triple_fault_event;
 static bool has_msr_mcg_ext_ctl;
 
 static int has_pmu_cap;
+/*
+ * Read from /sys/module/kvm/parameters/enable_pmu.
+ */
+static bool kvm_pmu_disabled;
 
 static struct kvm_cpuid2 *cpuid_cache;
 static struct kvm_cpuid2 *hv_cpuid_cache;
@@ -3256,6 +3260,7 @@  int kvm_arch_init(MachineState *ms, KVMState *s)
     int ret;
     struct utsname utsname;
     Error *local_err = NULL;
+    g_autofree char *kvm_enable_pmu;
 
     /*
      * Initialize SEV context, if required
@@ -3401,6 +3406,17 @@  int kvm_arch_init(MachineState *ms, KVMState *s)
 
     has_pmu_cap = kvm_check_extension(s, KVM_CAP_PMU_CAPABILITY);
 
+    /*
+     * 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 == 'N') {
+            kvm_pmu_disabled = true;
+        }
+    }
+
     return 0;
 }