[PATCH v4 11/15] s390/vfio-ap: Transition device migration state to STOP

[Anthony Krowiak <akrowiak@linux.ibm.com>]

Typically at this point, interrupt processing for the device, DMA and other
changes to the device's external state must be prohibited. For VFIO AP,
there is no physical DMA device virtualized by the vfio-ap device . It
merely manages the guest's AP configuration that identifies the devices
passed through to the guest, but does not have access to any of them. Those
AP devices are passed through and controlled exclusively by the SIE program
used to start the guest. There  only thing to do at this point is return
NULL to the caller since the file streams and associated data will get
cleaned up as a result of the VFIO migration framework releasing the files.

Signed-off-by: Anthony Krowiak <akrowiak@linux.ibm.com>
---
 drivers/s390/crypto/vfio_ap_migration.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/crypto/vfio_ap_migration.c b/drivers/s390/crypto/vfio_ap_migration.c
index 9cd1e7a3f743..1b526b743ad0 100644
--- a/drivers/s390/crypto/vfio_ap_migration.c
+++ b/drivers/s390/crypto/vfio_ap_migration.c
@@ -1159,12 +1159,17 @@ vfio_ap_transition_to_state(struct ap_matrix_mdev *matrix_mdev,
 		return filp;
 	}
 
+	/*
+	 * Terminates the data transfer session of the vfio-ap device state
+	 * between the source and target hosts. Since the vfio-ap device does
+	 * not virtualize a DMA device, there is no internal device state to
+	 * incorporate into the vfio-ap device on the target.
+	 */
 	if ((cur_state == VFIO_DEVICE_STATE_RESUMING &&
 	     new_state == VFIO_DEVICE_STATE_STOP) ||
 	    (cur_state == VFIO_DEVICE_STATE_STOP_COPY &&
 	     new_state == VFIO_DEVICE_STATE_STOP)) {
-		/* TODO */
-		return ERR_PTR(-EOPNOTSUPP);
+		return NULL;
 	}
 
 	if ((cur_state == VFIO_DEVICE_STATE_STOP &&
-- 
2.53.0