vmm: add nested option to CPU config

Add an option in the CLI to enable nested support.
Adding an option --cpu nested=on|off to the CPU
argument to enable nested support for Microsoft
Hypervisor. By default it is enabled for both KVM
and MSHV.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

vmm/src/vm_config.rs

@@ -69,6 +69,8 @@ pub struct CpusConfig {
     pub affinity: Option<Vec<CpuAffinity>>,
     #[serde(default)]
     pub features: CpuFeatures,
+    #[serde(default = "default_cpusconfig_nested")]
+    pub nested: bool,
 }
 
 pub const DEFAULT_VCPUS: u32 = 1;
@@ -83,6 +85,7 @@ impl Default for CpusConfig {
             max_phys_bits: DEFAULT_MAX_PHYS_BITS,
             affinity: None,
             features: CpuFeatures::default(),
+            nested: true,
         }
     }
 }
@@ -177,6 +180,10 @@ fn default_memoryconfig_thp() -> bool {
     true
 }
 
+fn default_cpusconfig_nested() -> bool {
+    true
+}
+
 #[derive(Clone, Debug, PartialEq, Eq, Deserialize, Serialize)]
 pub struct MemoryConfig {
     pub size: u64,