Implements the callback that sets a new migration state of a vfio device
during live migration of guests with pass-through access to AP devices.
This callback is mandatory for VFIO_DEVICE_FEATURE_MIGRATION
support.

The function pointer for this callback is specified via the
'migration_set_state' field of the 'vfio_migration_ops' structure
which is stored with the VFIO device when the 'vfio_device'
structure representing the mediated device is initialized.

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_migration.c | 87 ++++++++++++++++++++++++-
 1 file changed, 86 insertions(+), 1 deletion(-)

diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index 76cbbe1adb7a..a8b109bc5cf9 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -96,10 +96,95 @@ static void vfio_ap_release_mig_files(struct ap_matrix_mdev *matrix_mdev)
 	}
 }
 
+static struct file *
+vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
+			    enum vfio_device_mig_state new_state)
+{
+	struct vfio_ap_migration_data *mig_data;
+	enum vfio_device_mig_state cur_state;
+
+	lockdep_assert_held(&matrix_dev->mdevs_lock);
+	mig_data = matrix_mdev->mig_data;
+	cur_state = mig_data->mig_state;
+	dev_dbg(matrix_mdev->vdev.dev, "%s: %d -> %d\n", __func__, cur_state,
+		new_state);
+
+	if (cur_state == VFIO_DEVICE_STATE_STOP &&
+	    new_state == VFIO_DEVICE_STATE_STOP_COPY) {
+		/* TODO */
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+
+	if (cur_state == VFIO_DEVICE_STATE_STOP &&
+	    new_state == VFIO_DEVICE_STATE_RESUMING) {
+		/* TODO */
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+
+	if (cur_state == VFIO_DEVICE_STATE_RESUMING &&
+	    new_state == VFIO_DEVICE_STATE_STOP) {
+		/* TODO */
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+
+	if (cur_state == VFIO_DEVICE_STATE_STOP_COPY &&
+	    new_state == VFIO_DEVICE_STATE_STOP) {
+		/* TODO */
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+
+	if ((cur_state == VFIO_DEVICE_STATE_STOP &&
+	     new_state == VFIO_DEVICE_STATE_RUNNING) ||
+	    (cur_state == VFIO_DEVICE_STATE_RUNNING &&
+	     new_state == VFIO_DEVICE_STATE_STOP)) {
+		/* TODO */
+		return ERR_PTR(-EOPNOTSUPP);
+	}
+
+	/* vfio_mig_get_next_state() does not use arcs other than the above */
+	WARN_ON(true);
+
+	return ERR_PTR(-EINVAL);
+}
+
 static struct file *vfio_ap_set_state(struct vfio_device *vdev,
 				      enum vfio_device_mig_state  new_state)
 {
-	return NULL;
+	int ret;
+	struct file *filp = NULL;
+	struct ap_matrix_mdev *matrix_mdev;
+	enum vfio_device_mig_state next_state;
+	struct vfio_ap_migration_data *mig_data;
+
+	mutex_lock(&matrix_dev->mdevs_lock);
+	matrix_mdev = container_of(vdev, struct ap_matrix_mdev, vdev);
+	mig_data = matrix_mdev->mig_data;
+	dev_dbg(vdev->dev, "%s -> %d\n", __func__, new_state);
+
+	while (mig_data->mig_state != new_state) {
+		ret = vfio_mig_get_next_state(vdev, mig_data->mig_state,
+					      new_state, &next_state);
+		if (ret) {
+			filp = ERR_PTR(ret);
+			break;
+		}
+
+		filp = vfio_ap_transition_to_state(matrix_mdev, next_state);
+		if (IS_ERR(filp))
+			break;
+
+		mig_data->mig_state = next_state;
+
+		if (WARN_ON(filp && new_state != next_state)) {
+			fput(filp);
+			filp = ERR_PTR(-EINVAL);
+			break;
+		}
+	}
+
+	mutex_unlock(&matrix_dev->mdevs_lock);
+
+	return filp;
 }
 
 static int vfio_ap_get_state(struct vfio_device *vdev,
-- 
2.52.0