When migrating a VFIO device that supports pre-copy, it is transitioned
to STOP_COPY twice: once in vfio_vmstate_change() and second time in
vfio_save_complete_precopy().

The second transition is harmless, as it's a STOP_COPY->STOP_COPY no-op
transition. However, with the newly added VFIO migration QAPI event, the
STOP_COPY event is undesirably emitted twice.

Prevent this by returning early in vfio_migration_set_state() if
new_state is the same as current device state.

Note that the STOP_COPY transition in vfio_save_complete_precopy() is
essential for VFIO devices that don't support pre-copy, for migrating an
already stopped guest and for snapshots.

Signed-off-by: Avihai Horon <avihaih@nvidia.com>
Reviewed-by: Cédric Le Goater <clg@redhat.com>
---
 hw/vfio/migration.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/vfio/migration.c b/hw/vfio/migration.c
index 2e1a8f6031..f2b7a3067b 100644
--- a/hw/vfio/migration.c
+++ b/hw/vfio/migration.c
@@ -146,6 +146,10 @@ static int vfio_migration_set_state(VFIODevice *vbasedev,
         (struct vfio_device_feature_mig_state *)feature->data;
     int ret;
 
+    if (new_state == migration->device_state) {
+        return 0;
+    }
+
     feature->argsz = sizeof(buf);
     feature->flags =
         VFIO_DEVICE_FEATURE_SET | VFIO_DEVICE_FEATURE_MIG_DEVICE_STATE;
-- 
2.26.3