fix(vmm): drop uffd handle on handler disconnect

This is to unregister all UFFD ranges when the UFFD handler is
disconnected so that no further UFFD message is sent if the handler is
not longer available.

Signed-off-by: Nikita Kalyazin <[email protected]>

Author: kalyazin

src/vmm/src/lib.rs

@@ -844,6 +844,14 @@ impl Vmm {
         }
     }
 
+    fn hungup_event_in_uffd_socket(&self, source: RawFd, event_set: EventSet) -> bool {
+        if let Some(uffd_socket) = &self.uffd_socket {
+            uffd_socket.as_raw_fd() == source && (event_set == EventSet::IN | EventSet::HANG_UP)
+        } else {
+            false
+        }
+    }
+
     fn process_uffd_socket(&mut self) {
         const BUFFER_SIZE: usize = 4096;
 
@@ -985,7 +993,7 @@ impl Drop for Vmm {
 
 impl MutEventSubscriber for Vmm {
     /// Handle a read event (EPOLLIN).
-    fn process(&mut self, event: Events, _: &mut EventOps) {
+    fn process(&mut self, event: Events, ops: &mut EventOps) {
         let source = event.fd();
         let event_set = event.event_set();
 
@@ -1028,6 +1036,15 @@ impl MutEventSubscriber for Vmm {
         if self.active_event_in_uffd_socket(source, event_set) {
             self.process_uffd_socket();
         }
+
+        if self.hungup_event_in_uffd_socket(source, event_set) {
+            info!("UFFD handler process has disconnected.");
+
+            self.uffd = None;
+            if let Err(err) = ops.remove(Events::new(&source, EventSet::IN)) {
+                error!("Failed to unregister UFFD socket event: {}", err);
+            }
+        }
     }
 
     fn init(&mut self, ops: &mut EventOps) {