Various subsystems might need to take some steps before the KVM file descriptor
for a virtual machine is changed. So a new notifier is added to inform them that
kvm VM file descriptor is about to change.

Subsequent patches will add callback implementations for specific components
that need this notification.

Signed-off-by: Ani Sinha <anisinha@redhat.com>
---
 accel/kvm/kvm-all.c    | 25 +++++++++++++++++++++++++
 accel/stubs/kvm-stub.c |  8 ++++++++
 include/system/kvm.h   | 15 +++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index ef8e855af5..367968427b 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -127,6 +127,9 @@ static NotifierList kvm_irqchip_change_notifiers =
 static NotifierWithReturnList register_vmfd_changed_notifiers =
     NOTIFIER_WITH_RETURN_LIST_INITIALIZER(register_vmfd_changed_notifiers);
 
+static NotifierWithReturnList register_vmfd_pre_change_notifiers =
+    NOTIFIER_WITH_RETURN_LIST_INITIALIZER(register_vmfd_pre_change_notifiers);
+
 struct KVMResampleFd {
     int gsi;
     EventNotifier *resample_event;
@@ -2193,6 +2196,22 @@ static int kvm_vmfd_change_notify(Error **errp)
                                             &vmfd_notifier, errp);
 }
 
+void kvm_vmfd_add_pre_change_notifier(NotifierWithReturn *n)
+{
+    notifier_with_return_list_add(&register_vmfd_pre_change_notifiers, n);
+}
+
+void kvm_vmfd_remove_pre_change_notifier(NotifierWithReturn *n)
+{
+    notifier_with_return_remove(n);
+}
+
+static int kvm_vmfd_pre_change_notify(Error **errp)
+{
+    return notifier_with_return_list_notify(&register_vmfd_pre_change_notifiers,
+                                            NULL, errp);
+}
+
 int kvm_irqchip_get_virq(KVMState *s)
 {
     int next_virq;
@@ -2654,6 +2673,12 @@ static int kvm_reset_vmfd(MachineState *ms)
     memory_listener_unregister(&kml->listener);
     memory_listener_unregister(&kvm_io_listener);
 
+    ret = kvm_vmfd_pre_change_notify(&err);
+    if (ret < 0) {
+        return ret;
+    }
+    assert(!err);
+
     if (s->vmfd >= 0) {
         close(s->vmfd);
     }
diff --git a/accel/stubs/kvm-stub.c b/accel/stubs/kvm-stub.c
index a6e8a6e16c..7f4e3c4050 100644
--- a/accel/stubs/kvm-stub.c
+++ b/accel/stubs/kvm-stub.c
@@ -79,6 +79,14 @@ void kvm_irqchip_change_notify(void)
 {
 }
 
+void kvm_vmfd_add_pre_change_notifier(NotifierWithReturn *n)
+{
+}
+
+void kvm_vmfd_remove_pre_change_notifier(NotifierWithReturn *n)
+{
+}
+
 void kvm_vmfd_add_change_notifier(NotifierWithReturn *n)
 {
 }
diff --git a/include/system/kvm.h b/include/system/kvm.h
index 7df162b1f7..edc3fa5004 100644
--- a/include/system/kvm.h
+++ b/include/system/kvm.h
@@ -587,4 +587,19 @@ void kvm_vmfd_add_change_notifier(NotifierWithReturn *n);
  */
 void kvm_vmfd_remove_change_notifier(NotifierWithReturn *n);
 
+/**
+ * kvm_vmfd_add_pre_change_notifier - register a notifier to get notified when
+ * kvm vm file descriptor is about to be changed as a part of the confidential
+ * guest "reset" process.
+ * @n: notifier with return value.
+ */
+void kvm_vmfd_add_pre_change_notifier(NotifierWithReturn *n);
+
+/**
+ * kvm_vmfd_remove_pre_change_notifier - de-register a notifier previously
+ * registered with kvm_vmfd_add_pre_change_notifier.
+ * @n: the notifier that was previously registered.
+ */
+void kvm_vmfd_remove_pre_change_notifier(NotifierWithReturn *n);
+
 #endif
-- 
2.42.0