vhost-vdpa: uAPI to get dedicated descriptor group id

With _F_DESC_ASID backend feature, the device can now support the
VHOST_VDPA_GET_VRING_DESC_GROUP ioctl, and it may expose the descriptor
table (including avail and used ring) in a different group than the
buffers it contains. This new uAPI will fetch the group ID of the
descriptor table.
Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20231018171456.1624030-6-dtatulea@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Si-Wei Liu <si-wei.liu@oracle.com>
Tested-by: Si-Wei Liu <si-wei.liu@oracle.com>
Tested-by: Lei Yang <leiyang@redhat.com>

drivers/vhost/vdpa.c

@@ -613,6 +613,16 @@ static long vhost_vdpa_vring_ioctl(struct vhost_vdpa *v, unsigned int cmd,
 		else if (copy_to_user(argp, &s, sizeof(s)))
 			return -EFAULT;
 		return 0;
+	case VHOST_VDPA_GET_VRING_DESC_GROUP:
+		if (!vhost_vdpa_has_desc_group(v))
+			return -EOPNOTSUPP;
+		s.index = idx;
+		s.num = ops->get_vq_desc_group(vdpa, idx);
+		if (s.num >= vdpa->ngroups)
+			return -EIO;
+		else if (copy_to_user(argp, &s, sizeof(s)))
+			return -EFAULT;
+		return 0;
 	case VHOST_VDPA_SET_GROUP_ASID:
 		if (copy_from_user(&s, argp, sizeof(s)))
 			return -EFAULT;

include/uapi/linux/vhost.h

@@ -219,4 +219,12 @@
  */
 #define VHOST_VDPA_RESUME		_IO(VHOST_VIRTIO, 0x7E)
 
+/* Get the group for the descriptor table including driver & device areas
+ * of a virtqueue: read index, write group in num.
+ * The virtqueue index is stored in the index field of vhost_vring_state.
+ * The group ID of the descriptor table for this specific virtqueue
+ * is returned via num field of vhost_vring_state.
+ */
+#define VHOST_VDPA_GET_VRING_DESC_GROUP	_IOWR(VHOST_VIRTIO, 0x7F,	\
+					      struct vhost_vring_state)
 #endif