[PATCH vhost v6 10/10] virtio_ring: virtqueue_set_dma_premapped support disable

[Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>]

Now, the API virtqueue_set_dma_premapped just support to
enable premapped mode.

If we allow enabling the premapped dynamically, we should
make this API to support disable the premapped mode.

Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
---
 drivers/virtio/virtio_ring.c | 39 +++++++++++++++++++++++++++---------
 include/linux/virtio.h       |  2 +-
 2 files changed, 31 insertions(+), 10 deletions(-)

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 543204e26c5a..832fffd93f29 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -2792,6 +2792,7 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
 /**
  * virtqueue_set_dma_premapped - set the vring premapped mode
  * @_vq: the struct virtqueue we're talking about.
+ * @premapped: enable/disable the premapped mode.
  *
  * Enable the premapped mode of the vq.
  *
@@ -2808,11 +2809,15 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
  *
  * Returns zero or a negative error.
  * 0: success.
- * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
+ * -EINVAL:
+ *	vring does not use the dma api, so we can not enable premapped mode.
+ *	Or some descs are used, this is not called immediately after creating
+ *	the vq, or after vq reset.
  */
-int virtqueue_set_dma_premapped(struct virtqueue *_vq)
+int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool premapped)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
+	int err = 0;
 	u32 num;
 
 	START_USE(vq);
@@ -2824,24 +2829,40 @@ int virtqueue_set_dma_premapped(struct virtqueue *_vq)
 		return -EINVAL;
 	}
 
+	if (vq->vq.premapped == premapped) {
+		END_USE(vq);
+		return 0;
+	}
+
 	if (!vq->use_dma_api) {
 		END_USE(vq);
 		return -EINVAL;
 	}
 
-	vq->vq.premapped = true;
+	if (premapped) {
+		vq->vq.premapped = true;
+
+		if (vq->packed_ring) {
+			kfree(vq->packed.desc_dma);
+			vq->packed.desc_dma = NULL;
+		} else {
+			kfree(vq->split.desc_dma);
+			vq->split.desc_dma = NULL;
+		}
 
-	if (vq->packed_ring) {
-		kfree(vq->packed.desc_dma);
-		vq->packed.desc_dma = NULL;
 	} else {
-		kfree(vq->split.desc_dma);
-		vq->split.desc_dma = NULL;
+		if (vq->packed_ring)
+			err = vring_alloc_dma_split(&vq->split, false);
+		else
+			err = vring_alloc_dma_packed(&vq->packed, false);
+
+		if (!err)
+			vq->vq.premapped = false;
 	}
 
 	END_USE(vq);
 
-	return 0;
+	return err;
 }
 EXPORT_SYMBOL_GPL(virtqueue_set_dma_premapped);
 
diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 407277d5a16b..4b338590abf4 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h
@@ -82,7 +82,7 @@ bool virtqueue_enable_cb(struct virtqueue *vq);
 
 unsigned virtqueue_enable_cb_prepare(struct virtqueue *vq);
 
-int virtqueue_set_dma_premapped(struct virtqueue *_vq);
+int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool premapped);
 
 bool virtqueue_poll(struct virtqueue *vq, unsigned);
 
-- 
2.32.0.3.g01195cf9f