vmm: memory: Add prefault option when creating region

When CoW can be used, the VM restoration time is reduced, but the pages
are not populated. This can lead to some slowness from the guest when
accessing these pages.

Depending on the use case, we might prefer a slower boot time for better
performances from guest runtime. The way to achieve this is to prefault
the pages in this case, using the MAP_POPULATE flag along with CoW.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/vm.rs

@@ -360,9 +360,13 @@ impl Vm {
         vmm_path: PathBuf,
     ) -> Result<Self> {
         let (kvm, fd) = Vm::kvm_new()?;
-        let memory_manager =
-            MemoryManager::new(fd.clone(), &config.lock().unwrap().memory.clone(), None)
-                .map_err(Error::MemoryManager)?;
+        let memory_manager = MemoryManager::new(
+            fd.clone(),
+            &config.lock().unwrap().memory.clone(),
+            None,
+            false,
+        )
+        .map_err(Error::MemoryManager)?;
 
         Vm::new_from_memory_manager(
             config,