allocate and register io memory if initial_swiotlb_size != 0

Allocate the swiotlb region if requested via the /machine-config API
endpoint.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

src/vmm/src/builder.rs

@@ -235,6 +235,10 @@ pub fn build_microvm_for_boot(
         .allocate_guest_memory()
         .map_err(StartMicrovmError::GuestMemory)?;
 
+    let io_memory = vm_resources
+        .allocate_io_memory()
+        .map_err(StartMicrovmError::GuestMemory)?;
+
     // Clone the command-line so that a failed boot doesn't pollute the original.
     #[allow(unused_mut)]
     let mut boot_cmdline = boot_config.cmdline.clone();
@@ -258,6 +262,13 @@ pub fn build_microvm_for_boot(
             .map_err(StartMicrovmError::Internal)?;
     }
 
+    if let Some(io_memory) = io_memory {
+        vmm.vm
+            .register_io_region(io_memory)
+            .map_err(VmmError::Vm)
+            .map_err(StartMicrovmError::Internal)?;
+    }
+
     let entry_point = load_kernel(boot_config, vmm.guest_memory())?;
     let initrd = load_initrd_from_config(boot_config, vmm.guest_memory())?;