Subject: Re: [PATCH vhost v13 11/12] virtio_ring: introduce dma sync api for virtqueue

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 30 Nov 2023 04:45:58 -0500

On Thu, Aug 10, 2023 at 08:30:56PM +0800, Xuan Zhuo wrote:
> These API has been introduced:
> 
> * virtqueue_dma_need_sync
> * virtqueue_dma_sync_single_range_for_cpu
> * virtqueue_dma_sync_single_range_for_device
> 
> These APIs can be used together with the premapped mechanism to sync the
> DMA address.
> 
> Signed-off-by: Xuan Zhuo <[email-masked]>
> ---
>  drivers/virtio/virtio_ring.c | 76 ++++++++++++++++++++++++++++++++++++
>  include/linux/virtio.h       |  8 ++++
>  2 files changed, 84 insertions(+)
> 
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 916479c9c72c..81ecb29c88f1 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -3175,4 +3175,80 @@ int virtqueue_dma_mapping_error(struct virtqueue *_vq, dma_addr_t addr)
>  }
>  EXPORT_SYMBOL_GPL(virtqueue_dma_mapping_error);
>  
> +/**
> + * virtqueue_dma_need_sync - check a dma address needs sync
> + * @_vq: the struct virtqueue we're talking about.
> + * @addr: DMA address
> + *
> + * Check if the dma address mapped by the virtqueue_dma_map_* APIs needs to be
> + * synchronized
> + *
> + * return bool
> + */
> +bool virtqueue_dma_need_sync(struct virtqueue *_vq, dma_addr_t addr)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +
> +	if (!vq->use_dma_api)
> +		return false;
> +
> +	return dma_need_sync(vring_dma_dev(vq), addr);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_dma_need_sync);
> +
> +/**
> + * virtqueue_dma_sync_single_range_for_cpu - dma sync for cpu
> + * @_vq: the struct virtqueue we're talking about.
> + * @addr: DMA address
> + * @offset: DMA address offset
> + * @size: buf size for sync
> + * @dir: DMA direction
> + *
> + * Before calling this function, use virtqueue_dma_need_sync() to confirm that
> + * the DMA address really needs to be synchronized
> + *
> + */
> +void virtqueue_dma_sync_single_range_for_cpu(struct virtqueue *_vq,
> +					     dma_addr_t addr,
> +					     unsigned long offset, size_t size,
> +					     enum dma_data_direction dir)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct device *dev = vring_dma_dev(vq);
> +
> +	if (!vq->use_dma_api)
> +		return;
> +
> +	dma_sync_single_range_for_cpu(dev, addr, offset, size,
> +				      DMA_BIDIRECTIONAL);
> +}

Why did you use DMA_BIDIRECTIONAL here?
Why is "dir" ignored?

> +EXPORT_SYMBOL_GPL(virtqueue_dma_sync_single_range_for_cpu);
> +
> +/**
> + * virtqueue_dma_sync_single_range_for_device - dma sync for device
> + * @_vq: the struct virtqueue we're talking about.
> + * @addr: DMA address
> + * @offset: DMA address offset
> + * @size: buf size for sync
> + * @dir: DMA direction
> + *
> + * Before calling this function, use virtqueue_dma_need_sync() to confirm that
> + * the DMA address really needs to be synchronized
> + */
> +void virtqueue_dma_sync_single_range_for_device(struct virtqueue *_vq,
> +						dma_addr_t addr,
> +						unsigned long offset, size_t size,
> +						enum dma_data_direction dir)
> +{
> +	struct vring_virtqueue *vq = to_vvq(_vq);
> +	struct device *dev = vring_dma_dev(vq);
> +
> +	if (!vq->use_dma_api)
> +		return;
> +
> +	dma_sync_single_range_for_device(dev, addr, offset, size,
> +					 DMA_BIDIRECTIONAL);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_dma_sync_single_range_for_device);
> +
>  MODULE_LICENSE("GPL");

same question here.

> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 79e3c74391e0..1311a7fbe675 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -220,4 +220,12 @@ void virtqueue_dma_unmap_single_attrs(struct virtqueue *_vq, dma_addr_t addr,
>  				      size_t size, enum dma_data_direction dir,
>  				      unsigned long attrs);
>  int virtqueue_dma_mapping_error(struct virtqueue *_vq, dma_addr_t addr);
> +
> +bool virtqueue_dma_need_sync(struct virtqueue *_vq, dma_addr_t addr);
> +void virtqueue_dma_sync_single_range_for_cpu(struct virtqueue *_vq, dma_addr_t addr,
> +					     unsigned long offset, size_t size,
> +					     enum dma_data_direction dir);
> +void virtqueue_dma_sync_single_range_for_device(struct virtqueue *_vq, dma_addr_t addr,
> +						unsigned long offset, size_t size,
> +						enum dma_data_direction dir);
>  #endif /* _LINUX_VIRTIO_H */
> -- 
> 2.32.0.3.g01195cf9f