hypervisor: Add get_feature_msrs method

KVM defines feature MSRs as MSRs that expose host capabilities and
processor features.

CPU profiles will describe how to adjust such feature MSRs similarly to
how they describe CPUID modifications.

We thus introduce a method on the hypervisor trait that queries the
hypervisor for the supported feature MSRs.

This will later be used to obtain the feature MSRs that need to be
adjusted when a CPU profile is applied.

The method will also be used by the upcoming CPU profile generation
tool which will be introduced in a follow up PR.

Signed-off-by: Oliver Anderson <oliver.anderson@cyberus-technology.de>
On-behalf-of: SAP oliver.anderson@sap.com

hypervisor/src/kvm/mod.rs

@@ -1825,6 +1825,42 @@ impl hypervisor::Hypervisor for KvmHypervisor {
         Ok(v)
     }
 
+    #[cfg(target_arch = "x86_64")]
+    fn get_feature_msrs(&self) -> hypervisor::Result<Vec<MsrEntry>> {
+        let list = self
+            .kvm
+            .get_msr_feature_index_list()
+            .map_err(|e| hypervisor::HypervisorError::GetFeatureMsrs(e.into()))?;
+
+        let kvm_msrs: Vec<kvm_msr_entry> = list
+            .as_slice()
+            .iter()
+            .copied()
+            .map(|index| kvm_msr_entry {
+                index,
+                ..Default::default()
+            })
+            .collect();
+
+        let mut kvm_msrs = MsrEntries::from_entries(&kvm_msrs).unwrap();
+
+        let num_feature_msrs = self
+            .kvm
+            .get_msrs(&mut kvm_msrs)
+            .map_err(|e| hypervisor::HypervisorError::GetFeatureMsrs(e.into()))?;
+
+        if list.as_slice().len() == num_feature_msrs {
+            Ok(kvm_msrs
+                .as_slice()
+                .iter()
+                .copied()
+                .map(MsrEntry::from)
+                .collect())
+        } else {
+            Err(hypervisor::HypervisorError::GetFeatureMsrsPartial)
+        }
+    }
+
     #[cfg(target_arch = "aarch64")]
     ///
     /// Retrieve AArch64 host maximum IPA size supported by KVM.