vmm: Add support for enabling AMX in vm guests

AMX is an x86 extension adding hardware units for matrix
operations (int and float dot products). The goal of the extension is
to provide performance enhancements for these common operations.

On Linux, AMX requires requesting the permission from the kernel prior
to use. Guests wanting to make use of the feature need to have the
request made prior to starting the vm.

This change then adds the first --cpus features option amx that when
passed will enable AMX usage for guests (needs a 5.17+ kernel) or
exits with failure.

The activation is done in the CpuManager of the VMM thread as it
allows migration and snapshot/restore to work fairly painlessly for
AMX enabled workloads.

Signed-off-by: William Douglas <william.douglas@intel.com>

vmm/src/config.rs

@@ -54,6 +54,8 @@ pub enum Error {
     ParseRestoreSourceUrlMissing,
     /// Error parsing CPU options
     ParseCpus(OptionParserError),
+    /// Invalid CPU features
+    InvalidCpuFeatures(String),
     /// Error parsing memory options
     ParseMemory(OptionParserError),
     /// Error parsing memory zone options
@@ -267,7 +269,7 @@ impl fmt::Display for Error {
                 write!(f, "Error parsing --console: invalid console mode given")
             }
             ParseCpus(o) => write!(f, "Error parsing --cpus: {}", o),
-
+            InvalidCpuFeatures(o) => write!(f, "Invalid feature in --cpus features list: {}", o),
             ParseDevice(o) => write!(f, "Error parsing --device: {}", o),
             ParseDevicePathMissing => write!(f, "Error parsing --device: path missing"),
             ParseFileSystem(o) => write!(f, "Error parsing --fs: {}", o),
@@ -452,6 +454,12 @@ pub struct CpuAffinity {
     pub host_cpus: Vec<u8>,
 }
 
+#[derive(Clone, Debug, Default, PartialEq, Deserialize, Serialize)]
+pub struct CpuFeatures {
+    #[cfg(all(feature = "amx", target_arch = "x86_64"))]
+    pub amx: bool,
+}
+
 pub enum CpuTopologyParseError {
     InvalidValue(String),
 }
@@ -509,6 +517,8 @@ pub struct CpusConfig {
     pub max_phys_bits: u8,
     #[serde(default)]
     pub affinity: Option<Vec<CpuAffinity>>,
+    #[serde(default)]
+    pub features: CpuFeatures,
 }
 
 impl CpusConfig {
@@ -520,7 +530,8 @@ impl CpusConfig {
             .add("topology")
             .add("kvm_hyperv")
             .add("max_phys_bits")
-            .add("affinity");
+            .add("affinity")
+            .add("features");
         parser.parse(cpus).map_err(Error::ParseCpus)?;
 
         let boot_vcpus: u8 = parser
@@ -552,6 +563,27 @@ impl CpusConfig {
                     })
                     .collect()
             });
+        let features_list = parser
+            .convert::<StringList>("features")
+            .map_err(Error::ParseCpus)?
+            .unwrap_or_default();
+        // Some ugliness here as the features being checked might be disabled
+        // at compile time causing the below allow and the need to specify the
+        // ref type in the match.
+        // The issue will go away once kvm_hyperv is moved under the features
+        // list as it will always be checked for.
+        #[allow(unused_mut)]
+        let mut features = CpuFeatures::default();
+        for s in features_list.0 {
+            match <std::string::String as AsRef<str>>::as_ref(&s) {
+                #[cfg(all(feature = "amx", target_arch = "x86_64"))]
+                "amx" => {
+                    features.amx = true;
+                    Ok(())
+                }
+                _ => Err(Error::InvalidCpuFeatures(s)),
+            }?;
+        }
 
         Ok(CpusConfig {
             boot_vcpus,
@@ -560,6 +592,7 @@ impl CpusConfig {
             kvm_hyperv,
             max_phys_bits,
             affinity,
+            features,
         })
     }
 }
@@ -573,6 +606,7 @@ impl Default for CpusConfig {
             kvm_hyperv: false,
             max_phys_bits: DEFAULT_MAX_PHYS_BITS,
             affinity: None,
+            features: CpuFeatures::default(),
         }
     }
 }