vp_vdpa: allow set vq state to initial state after reset

We used to fail the set_vq_state() since it was not supported yet by
the virtio spec. But if the bus tries to set the state which is equal
to the device initial state after reset, we can let it go.

This is a must for virtio_vdpa() to set vq state during probe which is
required for some vDPA parents.
Signed-off-by: Jason Wang <jasowang@redhat.com>
Link: https://lore.kernel.org/r/20210602021536.39525-4-jasowang@redhat.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Eli Cohen <elic@nvidia.com>

drivers/vdpa/virtio_pci/vp_vdpa.c

@@ -210,13 +210,49 @@ static int vp_vdpa_get_vq_state(struct vdpa_device *vdpa, u16 qid,
 	return -EOPNOTSUPP;
 }
 
+static int vp_vdpa_set_vq_state_split(struct vdpa_device *vdpa,
+				      const struct vdpa_vq_state *state)
+{
+	const struct vdpa_vq_state_split *split = &state->split;
+
+	if (split->avail_index == 0)
+		return 0;
+
+	return -EOPNOTSUPP;
+}
+
+static int vp_vdpa_set_vq_state_packed(struct vdpa_device *vdpa,
+				       const struct vdpa_vq_state *state)
+{
+	const struct vdpa_vq_state_packed *packed = &state->packed;
+
+	if (packed->last_avail_counter == 1 &&
+	    packed->last_avail_idx == 0 &&
+	    packed->last_used_counter == 1 &&
+	    packed->last_used_idx == 0)
+		return 0;
+
+	return -EOPNOTSUPP;
+}
+
 static int vp_vdpa_set_vq_state(struct vdpa_device *vdpa, u16 qid,
 				const struct vdpa_vq_state *state)
 {
-	/* Note that this is not supported by virtio specification, so
-	 * we return -ENOPOTSUPP here. This means we can't support live
-	 * migration, vhost device start/stop.
+	struct virtio_pci_modern_device *mdev = vdpa_to_mdev(vdpa);
+
+	/* Note that this is not supported by virtio specification.
+	 * But if the state is by chance equal to the device initial
+	 * state, we can let it go.
 	 */
+	if ((vp_modern_get_status(mdev) & VIRTIO_CONFIG_S_FEATURES_OK) &&
+	    !vp_modern_get_queue_enable(mdev, qid)) {
+		if (vp_modern_get_driver_features(mdev) &
+		    BIT_ULL(VIRTIO_F_RING_PACKED))
+			return vp_vdpa_set_vq_state_packed(vdpa, state);
+		else
+			return vp_vdpa_set_vq_state_split(vdpa,	state);
+	}
+
 	return -EOPNOTSUPP;
 }