vm-allocator: free GSIs when they are no longer used

These changes free GSIs when they are no longer used. That way we
won't exhaust the available GSIs anymore when attaching and
detaching devices.

On-behalf-of: SAP sebastian.eydam@sap.com
Signed-off-by: Sebastian Eydam <sebastian.eydam@cyberus-technology.de>

Author: amphi

vm-allocator/src/gsi.rs

@@ -197,6 +197,11 @@ impl GsiAllocator {
         self.gsis.alloc()
     }
 
+    /// Frees a GSI
+    pub fn free_gsi(&mut self, vector: u32) -> Result<(), InterruptAllocError> {
+        self.gsis.free(vector)
+    }
+
     #[cfg(target_arch = "x86_64")]
     /// Allocate an IRQ
     pub fn allocate_irq(&mut self) -> Result<u32, InterruptAllocError> {

vm-allocator/src/system.rs

@@ -91,6 +91,11 @@ impl SystemAllocator {
         self.gsi_allocator.allocate_gsi()
     }
 
+    /// Frees the given GSI.
+    pub fn free_gsi(&mut self, vector: u32) -> Result<(), InterruptAllocError> {
+        self.gsi_allocator.free_gsi(vector)
+    }
+
     /// Reserves a section of `size` bytes of IO address space.
     pub fn allocate_io_addresses(
         &mut self,

vmm/src/interrupt.rs

@@ -24,19 +24,23 @@ struct InterruptRoute {
     gsi: u32,
     irq_fd: EventFd,
     registered: AtomicBool,
+    allocator: Arc<Mutex<SystemAllocator>>,
 }
 
 impl InterruptRoute {
-    pub fn new(allocator: &mut SystemAllocator) -> Result<Self> {
+    pub fn new(allocator: Arc<Mutex<SystemAllocator>>) -> Result<Self> {
         let irq_fd = EventFd::new(libc::EFD_NONBLOCK)?;
         let gsi = allocator
+            .lock()
+            .unwrap()
             .allocate_gsi()
             .map_err(|e| io::Error::other(format!("Failed allocating new GSI: {e}")))?;
 
         Ok(InterruptRoute {
             gsi,
             irq_fd,
             registered: AtomicBool::new(false),
+            allocator,
         })
     }
 
@@ -77,6 +81,12 @@ impl InterruptRoute {
     }
 }
 
+impl Drop for InterruptRoute {
+    fn drop(&mut self) {
+        let _ = self.allocator.lock().unwrap().free_gsi(self.gsi);
+    }
+}
+
 pub struct RoutingEntry {
     route: IrqRoutingEntry,
     masked: bool,
@@ -292,11 +302,10 @@ impl InterruptManager for MsiInterruptManager {
     type GroupConfig = MsiIrqGroupConfig;
 
     fn create_group(&self, config: Self::GroupConfig) -> Result<Arc<dyn InterruptSourceGroup>> {
-        let mut allocator = self.allocator.lock().unwrap();
         let mut irq_routes: HashMap<InterruptIndex, InterruptRoute> =
             HashMap::with_capacity(config.count as usize);
         for i in config.base..config.base + config.count {
-            irq_routes.insert(i, InterruptRoute::new(&mut allocator)?);
+            irq_routes.insert(i, InterruptRoute::new(self.allocator.clone())?);
         }
 
         Ok(Arc::new(MsiInterruptGroup::new(