vfio-ap: flag as compatible with balloon

vfio-ap devices do not pin any pages in the host. Therefore, they
are compatible with memory ballooning.

Flag them as compatible, so both vfio-ap and a balloon can be
used simultaneously.

Cc: qemu-stable@nongnu.org
Acked-by: NChristian Borntraeger <borntraeger@de.ibm.com>
Tested-by: NTony Krowiak <akrowiak@linux.ibm.com>
Reviewed-by: NHalil Pasic <pasic@linux.ibm.com>
Signed-off-by: NCornelia Huck <cohuck@redhat.com>

hw/vfio/ap.c

@@ -104,6 +104,14 @@ static void vfio_ap_realize(DeviceState *dev, Error **errp)
     vapdev->vdev.name = g_strdup_printf("%s", mdevid);
     vapdev->vdev.dev = dev;
 
+    /*
+     * vfio-ap devices operate in a way compatible with
+     * memory ballooning, as no pages are pinned in the host.
+     * This needs to be set before vfio_get_device() for vfio common to
+     * handle the balloon inhibitor.
+     */
+    vapdev->vdev.balloon_allowed = true;
+
     ret = vfio_get_device(vfio_group, mdevid, &vapdev->vdev, &local_err);
     if (ret) {
         goto out_get_dev_err;