On confidential guests when the KVM virtual machine file descriptor changes as
a part of the reset process, event file descriptors needs to be reassociated
with the new KVM VM file descriptor. This is achieved with the help of a
callback handler that gets called when KVM VM file descriptor changes during
the confidential guest reset process.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
---
 hw/hyperv/vmbus.c | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/hw/hyperv/vmbus.c b/hw/hyperv/vmbus.c
index 961406cdd6..4763c0aebc 100644
--- a/hw/hyperv/vmbus.c
+++ b/hw/hyperv/vmbus.c
@@ -19,6 +19,7 @@
 #include "hw/hyperv/vmbus.h"
 #include "hw/hyperv/vmbus-bridge.h"
 #include "hw/sysbus.h"
+#include "system/kvm.h"
 #include "exec/target_page.h"
 #include "trace.h"
 
@@ -247,6 +248,12 @@ struct VMBus {
      * interrupt page
      */
     EventNotifier notifier;
+
+    /*
+     * Notifier to inform when vmfd is changed as a part of confidential guest
+     * reset mechanism.
+     */
+    NotifierWithReturn vmbus_vmfd_change_notifier;
 };
 
 static bool gpadl_full(VMBusGpadl *gpadl)
@@ -2346,6 +2353,26 @@ static void vmbus_dev_unrealize(DeviceState *dev)
     free_channels(vdev);
 }
 
+/*
+ * If the KVM fd changes because of VM reset in confidential guests,
+ * reassociate event fd with the new KVM fd.
+ */
+static int vmbus_handle_vmfd_change(NotifierWithReturn *notifier,
+                                    void *data, Error** errp)
+{
+    VMBus *vmbus = container_of(notifier, VMBus,
+                                vmbus_vmfd_change_notifier);
+    int ret = 0;
+    ret = hyperv_set_event_flag_handler(VMBUS_EVENT_CONNECTION_ID,
+                                            &vmbus->notifier);
+    /* if we are only using userland event handler, it may already exist */
+    if (ret != 0 && ret != -EEXIST) {
+        error_setg(errp, "hyperv set event handler failed with %d", ret);
+    }
+
+    return ret;
+}
+
 static const Property vmbus_dev_props[] = {
     DEFINE_PROP_UUID("instanceid", VMBusDevice, instanceid),
 };
@@ -2428,6 +2455,9 @@ static void vmbus_realize(BusState *bus, Error **errp)
         goto clear_event_notifier;
     }
 
+    vmbus->vmbus_vmfd_change_notifier.notify = vmbus_handle_vmfd_change;
+    kvm_vmfd_add_change_notifier(&vmbus->vmbus_vmfd_change_notifier);
+
     return;
 
 clear_event_notifier:
-- 
2.42.0