vfio: Create a global KVM VFIO device for all VFIO devices

KVM does not support multiple KVM VFIO devices to be created when
trying to support multiple VFIO devices. This commit creates one
global KVM VFIO device being shared with every VFIO device, which
makes possible the support for passing several devices through the
VM.

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

vmm/src/vm.rs

@@ -256,6 +256,9 @@ pub enum DeviceManagerError {
 
     /// Failed to map VFIO MMIO region.
     VfioMapRegion(VfioPciError),
+
+    /// Failed to create the KVM device.
+    CreateKvmDevice(io::Error),
 }
 pub type DeviceManagerResult<T> = result::Result<T, DeviceManagerError>;
 
@@ -946,6 +949,17 @@ impl DeviceManager {
         Ok(())
     }
 
+    fn create_kvm_device(vm: &Arc<VmFd>) -> DeviceManagerResult<DeviceFd> {
+        let mut vfio_dev = kvm_bindings::kvm_create_device {
+            type_: kvm_bindings::kvm_device_type_KVM_DEV_TYPE_VFIO,
+            fd: 0,
+            flags: 0,
+        };
+
+        vm.create_device(&mut vfio_dev)
+            .map_err(DeviceManagerError::CreateKvmDevice)
+    }
+
     fn add_vfio_devices(
         memory: GuestMemoryMmap,
         allocator: &mut SystemAllocator,
@@ -956,9 +970,14 @@ impl DeviceManager {
         mem_slots: u32,
     ) -> DeviceManagerResult<()> {
         if let Some(device_list_cfg) = &vm_cfg.devices {
+            // Create the KVM VFIO device
+            let device_fd = DeviceManager::create_kvm_device(vm_fd)?;
+            let device_fd = Arc::new(device_fd);
+
             for device_cfg in device_list_cfg.iter() {
-                let vfio_device = VfioDevice::new(device_cfg.path, vm_fd, memory.clone())
-                    .map_err(DeviceManagerError::VfioCreate)?;
+                let vfio_device =
+                    VfioDevice::new(device_cfg.path, device_fd.clone(), memory.clone())
+                        .map_err(DeviceManagerError::VfioCreate)?;
 
                 let mut vfio_pci_device = VfioPciDevice::new(vm_fd, allocator, vfio_device)
                     .map_err(DeviceManagerError::VfioPciCreate)?;