On Thu, 12 Oct 2023 05:15:52 -0400, "Michael S. Tsirkin" [off-list ref] wrote:

On Wed, Oct 11, 2023 at 05:27:07PM +0800, Xuan Zhuo wrote:

quoted

virtqueue_set_dma_premapped() adds a new parameter to disable the
virtqueue premapped mode.

Signed-off-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
---
 drivers/net/virtio_net.c     |  2 +-
 drivers/virtio/virtio_ring.c | 11 ++++++++---
 include/linux/virtio.h       |  2 +-
 3 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index fe7f314d65c9..6b5f47ebf9b2 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c

@@ -737,7 +737,7 @@ static void virtnet_rq_set_premapped(struct virtnet_info *vi)
 		return;

 	for (i = 0; i < vi->max_queue_pairs; i++) {
-		if (virtqueue_set_dma_premapped(vi->rq[i].vq))
+		if (virtqueue_set_dma_premapped(vi->rq[i].vq, true))
 			continue;

 		vi->rq[i].do_dma = true;

diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 51d8f3299c10..b3ded56722f4 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c

@@ -2784,7 +2784,7 @@ EXPORT_SYMBOL_GPL(virtqueue_resize);
  * 0: success.
  * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
  */
-int virtqueue_set_dma_premapped(struct virtqueue *_vq)
+int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool mode)
 {
 	struct vring_virtqueue *vq = to_vvq(_vq);
 	u32 num;

@@ -2803,8 +2803,13 @@ int virtqueue_set_dma_premapped(struct virtqueue *_vq)
 		return -EINVAL;
 	}

-	vq->premapped = true;
-	vq->do_unmap = false;
+	if (mode) {
+		vq->premapped = true;
+		vq->do_unmap = false;
+	} else {
+		vq->premapped = false;
+		vq->do_unmap = vq->use_dma_api;
+	}

 	END_USE(vq);

diff --git a/include/linux/virtio.h b/include/linux/virtio.h
index 4cc614a38376..1cf7b004348b 100644
--- a/include/linux/virtio.h
+++ b/include/linux/virtio.h

@@ -81,7 +81,7 @@ 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 mode);

 bool virtqueue_poll(struct virtqueue *vq, unsigned);

Wait a sec I thought we never change premapped. If you make this
dynamic don't you need a bunch of locking?
Or maybe queue is empty when you change this?
If yes pls add a bunch of BUG_ON checks to make sure this is not misused.

Actually, this api is called immediately after the vq init or vq reset.

We already have such a check.

Thanks.

/**
 * virtqueue_set_dma_premapped - set the vring premapped mode
 * @_vq: the struct virtqueue we're talking about.
 *
 * Enable the premapped mode of the vq.
 *
 * The vring in premapped mode does not do dma internally, so the driver must
 * do dma mapping in advance. The driver must pass the dma_address through
 * dma_address of scatterlist. When the driver got a used buffer from
 * the vring, it has to unmap the dma address.
 *
 * This function must be called immediately after creating the vq, or after vq
 * reset, and before adding any buffers to it.
 *
 * Caller must ensure we don't call this with other virtqueue operations
 * at the same time (except where noted).
 *
 * Returns zero or a negative error.
 * 0: success.
 * -EINVAL: vring does not use the dma api, so we can not enable premapped mode.
 */
int virtqueue_set_dma_premapped(struct virtqueue *_vq, bool mode)
{
	struct vring_virtqueue *vq = to_vvq(_vq);
	u32 num;

	START_USE(vq);

	num = vq->packed_ring ? vq->packed.vring.num : vq->split.vring.num;

-->	if (num != vq->vq.num_free) {
		END_USE(vq);
		return -EINVAL;
	}

	if (!vq->use_dma_api) {
		END_USE(vq);
		return -EINVAL;
	}

	if (mode) {
		vq->premapped = true;
		vq->do_unmap = false;
	} else {
		vq->premapped = false;
		vq->do_unmap = vq->use_dma_api;
	}

	END_USE(vq);

	return 0;
}
EXPORT_SYMBOL_GPL(virtqueue_set_dma_premapped);

quoted

--
2.32.0.3.g01195cf9f