vmnet: stop recieving events when VM is stopped

When the VM is stopped using the HMP command "stop", soon the handler will
stop reading from the vmnet interface. This causes a flood of
`VMNET_INTERFACE_PACKETS_AVAILABLE` events to arrive and puts the host CPU
at 100%. We fix this by removing the event handler from vmnet when the VM
is no longer in a running state and restore it when we return to a running
state.

Signed-off-by: Joelle van Dyne <j@getutm.app>
Signed-off-by: Jason Wang <jasowang@redhat.com>

net/vmnet-common.m

@@ -17,6 +17,7 @@
 #include "clients.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
+#include "sysemu/runstate.h"
 
 #include <vmnet/vmnet.h>
 #include <dispatch/dispatch.h>
@@ -242,6 +243,35 @@ static void vmnet_bufs_init(VmnetState *s)
     }
 }
 
+/**
+ * Called on state change to un-register/re-register handlers
+ */
+static void vmnet_vm_state_change_cb(void *opaque, bool running, RunState state)
+{
+    VmnetState *s = opaque;
+
+    if (running) {
+        vmnet_interface_set_event_callback(
+            s->vmnet_if,
+            VMNET_INTERFACE_PACKETS_AVAILABLE,
+            s->if_queue,
+            ^(interface_event_t event_id, xpc_object_t event) {
+                assert(event_id == VMNET_INTERFACE_PACKETS_AVAILABLE);
+                /*
+                 * This function is being called from a non qemu thread, so
+                 * we only schedule a BH, and do the rest of the io completion
+                 * handling from vmnet_send_bh() which runs in a qemu context.
+                 */
+                qemu_bh_schedule(s->send_bh);
+            });
+    } else {
+        vmnet_interface_set_event_callback(
+            s->vmnet_if,
+            VMNET_INTERFACE_PACKETS_AVAILABLE,
+            NULL,
+            NULL);
+    }
+}
 
 int vmnet_if_create(NetClientState *nc,
                     xpc_object_t if_desc,
@@ -329,19 +359,9 @@ int vmnet_if_create(NetClientState *nc,
     s->packets_send_current_pos = 0;
     s->packets_send_end_pos = 0;
 
-    vmnet_interface_set_event_callback(
-        s->vmnet_if,
-        VMNET_INTERFACE_PACKETS_AVAILABLE,
-        s->if_queue,
-        ^(interface_event_t event_id, xpc_object_t event) {
-            assert(event_id == VMNET_INTERFACE_PACKETS_AVAILABLE);
-            /*
-             * This function is being called from a non qemu thread, so
-             * we only schedule a BH, and do the rest of the io completion
-             * handling from vmnet_send_bh() which runs in a qemu context.
-             */
-            qemu_bh_schedule(s->send_bh);
-        });
+    vmnet_vm_state_change_cb(s, 1, RUN_STATE_RUNNING);
+
+    s->change = qemu_add_vm_change_state_handler(vmnet_vm_state_change_cb, s);
 
     return 0;
 }
@@ -356,6 +376,8 @@ void vmnet_cleanup_common(NetClientState *nc)
         return;
     }
 
+    vmnet_vm_state_change_cb(s, 0, RUN_STATE_SHUTDOWN);
+    qemu_del_vm_change_state_handler(s->change);
     if_stopped_sem = dispatch_semaphore_create(0);
     vmnet_stop_interface(
         s->vmnet_if,

net/vmnet_int.h

@@ -45,6 +45,8 @@ typedef struct VmnetState {
     int packets_send_end_pos;
 
     struct iovec iov_buf[VMNET_PACKETS_LIMIT];
+
+    VMChangeStateEntry *change;
 } VmnetState;
 
 const char *vmnet_status_map_str(vmnet_return_t status);