arch, hypervisor: Populate CPUID leaf 0x4000_0010 (TSC frequency)

This hypervisor leaf includes details of the TSC frequency if that is
available from KVM. This can be used to efficiently calculate time
passed when there is an invariant TSC.

TEST=Run `cpuid` in the guest and observe the frequency populated.

Fixes: #5178

Signed-off-by: Rob Bradford <robert.bradford@intel.com>

hypervisor/src/cpu.rs

@@ -237,6 +237,12 @@ pub enum HypervisorCpuError {
     ///
     #[error("Failed to initialize PMU")]
     InitializePmu,
+    #[cfg(target_arch = "x86_64")]
+    ///
+    /// Error getting TSC frequency
+    ///
+    #[error("Failed to get TSC frequency: {0}")]
+    GetTscKhz(#[source] anyhow::Error),
 }
 
 #[derive(Debug)]
@@ -432,4 +438,11 @@ pub trait Vcpu: Send + Sync {
     /// Return the list of initial MSR entries for a VCPU
     ///
     fn boot_msr_entries(&self) -> Vec<MsrEntry>;
+    #[cfg(target_arch = "x86_64")]
+    ///
+    /// Get the frequency of the TSC if available
+    ///
+    fn tsc_khz(&self) -> Result<Option<u32>> {
+        Ok(None)
+    }
 }

hypervisor/src/kvm/mod.rs

@@ -2156,6 +2156,23 @@ impl cpu::Vcpu for KvmVcpu {
             .set_device_attr(&cpu_attr)
             .map_err(|_| cpu::HypervisorCpuError::InitializePmu)
     }
+
+    #[cfg(target_arch = "x86_64")]
+    ///
+    /// Get the frequency of the TSC if available
+    ///
+    fn tsc_khz(&self) -> cpu::Result<Option<u32>> {
+        match self.fd.get_tsc_khz() {
+            Err(e) => {
+                if e.errno() == libc::EIO {
+                    Ok(None)
+                } else {
+                    Err(cpu::HypervisorCpuError::GetTscKhz(e.into()))
+                }
+            }
+            Ok(v) => Ok(Some(v)),
+        }
+    }
 }
 
 impl KvmVcpu {

hypervisor/src/kvm/x86_64/mod.rs

@@ -50,6 +50,9 @@ pub fn check_required_kvm_extensions(kvm: &Kvm) -> KvmResult<()> {
     if !kvm.check_extension(Cap::ImmediateExit) {
         return Err(KvmError::CapabilityMissing(Cap::ImmediateExit));
     }
+    if !kvm.check_extension(Cap::GetTscKhz) {
+        return Err(KvmError::CapabilityMissing(Cap::GetTscKhz));
+    }
     Ok(())
 }
 #[derive(Clone, Serialize, Deserialize)]