vmm: only use KVM_ARM_VCPU_PMU_V3 if available

Having PMU in guests isn't critical, and not all hardware supports
it (e.g. Apple Silicon).

CpuManager::init_pmu already has a fallback for if PMU is not
supported by the VCPU, but we weren't getting that far, because we
would always try to initialise the VCPU with KVM_ARM_VCPU_PMU_V3, and
then bail when it returned with EINVAL.

Signed-off-by: Alyssa Ross <hi@alyssa.is>

Cargo.toml

@@ -52,6 +52,7 @@ vm-memory = "0.10.0"
 # List of patched crates
 [patch.crates-io]
 kvm-bindings = { git = "https://github.com/cloud-hypervisor/kvm-bindings", branch = "ch-v0.6.0-tdx" }
+kvm-ioctls = { git = "https://github.com/rust-vmm/kvm-ioctls", branch = "main" }
 versionize_derive = { git = "https://github.com/cloud-hypervisor/versionize_derive", branch = "ch" }
 
 [dev-dependencies]

hypervisor/src/kvm/mod.rs

@@ -330,7 +330,7 @@ impl KvmVm {
         Ok(VfioDeviceFd::new_from_kvm(device_fd))
     }
     /// Checks if a particular `Cap` is available.
-    fn check_extension(&self, c: Cap) -> bool {
+    pub fn check_extension(&self, c: Cap) -> bool {
         self.fd.check_extension(c)
     }
 }

vmm/src/cpu.rs

@@ -52,6 +52,8 @@ use hypervisor::arch::x86::MsrEntry;
 use hypervisor::arch::x86::{SpecialRegisters, StandardRegisters};
 #[cfg(target_arch = "aarch64")]
 use hypervisor::kvm::kvm_bindings;
+#[cfg(all(target_arch = "aarch64", feature = "kvm"))]
+use hypervisor::kvm::kvm_ioctls::Cap;
 #[cfg(feature = "tdx")]
 use hypervisor::kvm::{TdxExitDetails, TdxExitStatus};
 use hypervisor::{CpuState, HypervisorCpuError, HypervisorType, VmExit, VmOps};
@@ -370,7 +372,14 @@ impl Vcpu {
             .map_err(Error::VcpuArmPreferredTarget)?;
         // We already checked that the capability is supported.
         kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PSCI_0_2;
-        kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PMU_V3;
+        if vm
+            .as_any()
+            .downcast_ref::<hypervisor::kvm::KvmVm>()
+            .unwrap()
+            .check_extension(Cap::ArmPmuV3)
+        {
+            kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_PMU_V3;
+        }
         // Non-boot cpus are powered off initially.
         if self.id > 0 {
             kvi.features[0] |= 1 << kvm_bindings::KVM_ARM_VCPU_POWER_OFF;