vmm: Break the cyclic dependency between DeviceManager and IO bus

By inserting the DeviceManager on the IO bus, we introduced some cyclic
dependency:

  DeviceManager ---> AddressManager ---> Bus ---> BusDevice
        ^                                             |
        |                                             |
        +---------------------------------------------+

This cycle needs to be broken by inserting a Weak reference instead of
an Arc (considered as a strong reference).

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

vmm/src/cpu.rs

@@ -507,7 +507,7 @@ impl CpuManager {
         let cpu_manager = Arc::new(Mutex::new(CpuManager {
             boot_vcpus,
             max_vcpus,
-            io_bus: Arc::downgrade(&device_manager.io_bus().clone()),
+            io_bus: Arc::downgrade(&device_manager.io_bus()),
             mmio_bus: device_manager.mmio_bus().clone(),
             ioapic: device_manager.ioapic().clone(),
             vm_memory: guest_memory,

vmm/src/device_manager.rs

@@ -39,7 +39,6 @@ use std::io::{self, sink, stdout};
 use std::os::unix::fs::OpenOptionsExt;
 use std::path::PathBuf;
 use std::result;
-#[cfg(feature = "pci_support")]
 use std::sync::Weak;
 use std::sync::{Arc, Mutex};
 use tempfile::NamedTempFile;
@@ -278,7 +277,7 @@ impl Console {
 
 struct AddressManager {
     allocator: Arc<Mutex<SystemAllocator>>,
-    io_bus: Arc<devices::Bus>,
+    io_bus: Weak<devices::Bus>,
     mmio_bus: Arc<devices::Bus>,
     vm_fd: Arc<VmFd>,
 }
@@ -311,6 +310,8 @@ impl DeviceRelocation for AddressManager {
 
                 // Update PIO bus
                 self.io_bus
+                    .upgrade()
+                    .unwrap()
                     .update_range(old_base, len, new_base, len)
                     .map_err(|e| io::Error::new(io::ErrorKind::Other, e))?;
             }
@@ -461,6 +462,7 @@ pub struct DeviceManager {
 }
 
 impl DeviceManager {
+    #[allow(clippy::too_many_arguments)]
     pub fn new(
         vm_fd: Arc<VmFd>,
         config: Arc<Mutex<VmConfig>>,
@@ -469,10 +471,8 @@ impl DeviceManager {
         _exit_evt: &EventFd,
         reset_evt: &EventFd,
         vmm_path: PathBuf,
+        io_bus: &Arc<devices::Bus>,
     ) -> DeviceManagerResult<Arc<Mutex<Self>>> {
-        let io_bus = devices::Bus::new();
-        let mmio_bus = devices::Bus::new();
-
         let mut virtio_devices: Vec<(Arc<Mutex<dyn vm_virtio::VirtioDevice>>, bool)> = Vec::new();
         let migratable_devices: Vec<Arc<Mutex<dyn Migratable>>> = Vec::new();
         let mut _mmap_regions = Vec::new();
@@ -482,8 +482,8 @@ impl DeviceManager {
 
         let address_manager = Arc::new(AddressManager {
             allocator,
-            io_bus: Arc::new(io_bus),
+            io_bus: Arc::downgrade(io_bus),
-            mmio_bus: Arc::new(mmio_bus),
+            mmio_bus: Arc::new(devices::Bus::new()),
             vm_fd: vm_fd.clone(),
         });
 
@@ -527,6 +527,8 @@ impl DeviceManager {
         #[cfg(feature = "acpi")]
         address_manager
             .io_bus
+            .upgrade()
+            .unwrap()
             .insert(memory_manager.clone(), 0xa00, 0x18)
             .map_err(DeviceManagerError::BusError)?;
 
@@ -597,6 +599,8 @@ impl DeviceManager {
         #[cfg(feature = "acpi")]
         address_manager
             .io_bus
+            .upgrade()
+            .unwrap()
             .insert(
                 Arc::clone(&device_manager) as Arc<Mutex<dyn BusDevice>>,
                 0xae00,
@@ -670,6 +674,8 @@ impl DeviceManager {
             let pci_config_io = Arc::new(Mutex::new(PciConfigIo::new(Arc::clone(&pci_bus))));
             self.address_manager
                 .io_bus
+                .upgrade()
+                .unwrap()
                 .insert(pci_config_io, 0xcf8, 0x8)
                 .map_err(DeviceManagerError::BusError)?;
             let pci_config_mmio = Arc::new(Mutex::new(PciConfigMmio::new(Arc::clone(&pci_bus))));
@@ -752,6 +758,8 @@ impl DeviceManager {
 
         self.address_manager
             .io_bus
+            .upgrade()
+            .unwrap()
             .insert(acpi_device, 0x3c0, 0x4)
             .map_err(DeviceManagerError::BusError)?;
 
@@ -783,6 +791,8 @@ impl DeviceManager {
 
         self.address_manager
             .io_bus
+            .upgrade()
+            .unwrap()
             .insert(ged_device.clone(), 0xb000, 0x1)
             .map_err(DeviceManagerError::BusError)?;
         Ok(Some(ged_device))
@@ -794,6 +804,8 @@ impl DeviceManager {
 
         self.address_manager
             .io_bus
+            .upgrade()
+            .unwrap()
             .insert(i8042, 0x61, 0x4)
             .map_err(DeviceManagerError::BusError)?;
         #[cfg(feature = "cmos")]
@@ -819,6 +831,8 @@ impl DeviceManager {
 
             self.address_manager
                 .io_bus
+                .upgrade()
+                .unwrap()
                 .insert(cmos, 0x70, 0x2)
                 .map_err(DeviceManagerError::BusError)?;
         }
@@ -864,6 +878,8 @@ impl DeviceManager {
 
             self.address_manager
                 .io_bus
+                .upgrade()
+                .unwrap()
                 .insert(serial.clone(), 0x3f8, 0x8)
                 .map_err(DeviceManagerError::BusError)?;
 
@@ -1429,7 +1445,7 @@ impl DeviceManager {
 
         pci.register_mapping(
             vfio_pci_device,
-            self.address_manager.io_bus.as_ref(),
+            self.address_manager.io_bus.upgrade().unwrap().as_ref(),
             self.address_manager.mmio_bus.as_ref(),
             bars,
         )
@@ -1534,7 +1550,7 @@ impl DeviceManager {
 
         pci.register_mapping(
             virtio_pci_device.clone(),
-            self.address_manager.io_bus.as_ref(),
+            self.address_manager.io_bus.upgrade().unwrap().as_ref(),
             self.address_manager.mmio_bus.as_ref(),
             bars,
         )
@@ -1606,8 +1622,8 @@ impl DeviceManager {
         Ok(())
     }
 
-    pub fn io_bus(&self) -> &Arc<devices::Bus> {
+    pub fn io_bus(&self) -> Arc<devices::Bus> {
-        &self.address_manager.io_bus
+        Arc::clone(&self.address_manager.io_bus.upgrade().unwrap())
     }
 
     pub fn mmio_bus(&self) -> &Arc<devices::Bus> {

vmm/src/vm.rs

@@ -222,6 +222,8 @@ pub struct Vm {
     state: RwLock<VmState>,
     cpu_manager: Arc<Mutex<cpu::CpuManager>>,
     memory_manager: Arc<Mutex<MemoryManager>>,
+    // Hold the strong reference onto the IO bus.
+    _io_bus: Arc<devices::Bus>,
 }
 
 impl Vm {
@@ -329,6 +331,8 @@ impl Vm {
             .ok_or(Error::CreateSystemAllocator)?,
         ));
 
+        let io_bus = Arc::new(devices::Bus::new());
+
         let memory_config = config.lock().unwrap().memory.clone();
 
         let memory_manager = MemoryManager::new(
@@ -351,6 +355,7 @@ impl Vm {
             &exit_evt,
             &reset_evt,
             vmm_path,
+            &io_bus,
         )
         .map_err(Error::DeviceManager)?;
 
@@ -379,6 +384,7 @@ impl Vm {
             state: RwLock::new(VmState::Created),
             cpu_manager,
             memory_manager,
+            _io_bus: io_bus,
         })
     }