Re: [PATCH V4 9/9] vduse: switch to use virtio map API instead of DMA API

["Michael S. Tsirkin" <mst@redhat.com>]

On Fri, Jul 18, 2025 at 05:16:16PM +0800, Jason Wang wrote:
> Lacking the support of device specific mapping supported in virtio,
> VDUSE must trick the DMA API in order to make virtio-vdpa transport
> work. This is done by advertising vDPA device as dma device with a
> VDUSE specific dma_ops even if it doesn't do DMA at all.
> 
> This will be fixed by this patch. Thanks to the new mapping operations
> support by virtio and vDPA. VDUSE can simply switch to advertise its
> specific mappings operations to virtio via virtio-vdpa then DMA API is
> not needed for VDUSE any more.
> 
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Jason Wang <jasowang@redhat.com>

So with all this, how do we know we did not forget any
users of dma api?


> ---
>  drivers/vdpa/Kconfig                 |  8 +------
>  drivers/vdpa/vdpa_user/iova_domain.c |  2 +-
>  drivers/vdpa/vdpa_user/iova_domain.h |  2 +-
>  drivers/vdpa/vdpa_user/vduse_dev.c   | 31 ++++++++++++++++------------
>  4 files changed, 21 insertions(+), 22 deletions(-)
> 
> diff --git a/drivers/vdpa/Kconfig b/drivers/vdpa/Kconfig
> index 559fb9d3271f..857cf288c876 100644
> --- a/drivers/vdpa/Kconfig
> +++ b/drivers/vdpa/Kconfig
> @@ -34,13 +34,7 @@ config VDPA_SIM_BLOCK
>  
>  config VDPA_USER
>  	tristate "VDUSE (vDPA Device in Userspace) support"
> -	depends on EVENTFD && MMU && HAS_DMA
> -	#
> -	# This driver incorrectly tries to override the dma_ops.  It should
> -	# never have done that, but for now keep it working on architectures
> -	# that use dma ops
> -	#
> -	depends on ARCH_HAS_DMA_OPS
> +	depends on EVENTFD && MMU
>  	select VHOST_IOTLB
>  	select IOMMU_IOVA
>  	help
> diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
> index 019f3305c0ac..8ea311692545 100644
> --- a/drivers/vdpa/vdpa_user/iova_domain.c
> +++ b/drivers/vdpa/vdpa_user/iova_domain.c
> @@ -447,7 +447,7 @@ void vduse_domain_unmap_page(struct vduse_iova_domain *domain,
>  
>  void *vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
>  				  size_t size, dma_addr_t *dma_addr,
> -				  gfp_t flag, unsigned long attrs)
> +				  gfp_t flag)
>  {
>  	struct iova_domain *iovad = &domain->consistent_iovad;
>  	unsigned long limit = domain->iova_limit;
> diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h
> index 846572b95c23..a2316571671f 100644
> --- a/drivers/vdpa/vdpa_user/iova_domain.h
> +++ b/drivers/vdpa/vdpa_user/iova_domain.h
> @@ -64,7 +64,7 @@ void vduse_domain_unmap_page(struct vduse_iova_domain *domain,
>  
>  void *vduse_domain_alloc_coherent(struct vduse_iova_domain *domain,
>  				  size_t size, dma_addr_t *dma_addr,
> -				  gfp_t flag, unsigned long attrs);
> +				  gfp_t flag);
>  
>  void vduse_domain_free_coherent(struct vduse_iova_domain *domain, size_t size,
>  				void *vaddr, dma_addr_t dma_addr,
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 934c50d15b28..d858c4389cc1 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -814,51 +814,55 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
>  	.free			= vduse_vdpa_free,
>  };
>  
> -static void vduse_dev_sync_single_for_device(struct device *dev,
> +static void vduse_dev_sync_single_for_device(void *token,
>  					     dma_addr_t dma_addr, size_t size,
>  					     enum dma_data_direction dir)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  
>  	vduse_domain_sync_single_for_device(domain, dma_addr, size, dir);
>  }
>  
> -static void vduse_dev_sync_single_for_cpu(struct device *dev,
> +static void vduse_dev_sync_single_for_cpu(void *token,
>  					     dma_addr_t dma_addr, size_t size,
>  					     enum dma_data_direction dir)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  
>  	vduse_domain_sync_single_for_cpu(domain, dma_addr, size, dir);
>  }
>  
> -static dma_addr_t vduse_dev_map_page(struct device *dev, struct page *page,
> +static dma_addr_t vduse_dev_map_page(void *token, struct page *page,
>  				     unsigned long offset, size_t size,
>  				     enum dma_data_direction dir,
>  				     unsigned long attrs)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  
>  	return vduse_domain_map_page(domain, page, offset, size, dir, attrs);
>  }
>  
> -static void vduse_dev_unmap_page(struct device *dev, dma_addr_t dma_addr,
> +static void vduse_dev_unmap_page(void *token, dma_addr_t dma_addr,
>  				size_t size, enum dma_data_direction dir,
>  				unsigned long attrs)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  
>  	return vduse_domain_unmap_page(domain, dma_addr, size, dir, attrs);
>  }
>  
> -static void *vduse_dev_alloc_coherent(struct device *dev, size_t size,
> -					dma_addr_t *dma_addr, gfp_t flag,
> -					unsigned long attrs)
> +static void *vduse_dev_alloc_coherent(void *token, size_t size,
> +				      dma_addr_t *dma_addr, gfp_t flag)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  	unsigned long iova;
> @@ -866,7 +870,7 @@ static void *vduse_dev_alloc_coherent(struct device *dev, size_t size,
>  
>  	*dma_addr = DMA_MAPPING_ERROR;
>  	addr = vduse_domain_alloc_coherent(domain, size,
> -				(dma_addr_t *)&iova, flag, attrs);
> +					   (dma_addr_t *)&iova, flag);
>  	if (!addr)
>  		return NULL;
>  
> @@ -875,25 +879,27 @@ static void *vduse_dev_alloc_coherent(struct device *dev, size_t size,
>  	return addr;
>  }
>  
> -static void vduse_dev_free_coherent(struct device *dev, size_t size,
> +static void vduse_dev_free_coherent(void *token, size_t size,
>  					void *vaddr, dma_addr_t dma_addr,
>  					unsigned long attrs)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  
>  	vduse_domain_free_coherent(domain, size, vaddr, dma_addr, attrs);
>  }
>  
> -static size_t vduse_dev_max_mapping_size(struct device *dev)
> +static size_t vduse_dev_max_mapping_size(void *token)
>  {
> +	struct device *dev = token;
>  	struct vduse_dev *vdev = dev_to_vduse(dev);
>  	struct vduse_iova_domain *domain = vdev->domain;
>  
>  	return domain->bounce_size;
>  }
>  
> -static const struct dma_map_ops vduse_dev_dma_ops = {
> +static const struct virtio_map_ops vduse_map_ops = {
>  	.sync_single_for_device = vduse_dev_sync_single_for_device,
>  	.sync_single_for_cpu = vduse_dev_sync_single_for_cpu,
>  	.map_page = vduse_dev_map_page,
> @@ -2009,7 +2015,7 @@ static int vduse_dev_init_vdpa(struct vduse_dev *dev, const char *name)
>  		return -EEXIST;
>  
>  	vdev = vdpa_alloc_device(struct vduse_vdpa, vdpa, dev->dev,
> -				 &vduse_vdpa_config_ops, NULL,
> +				 &vduse_vdpa_config_ops, &vduse_map_ops,
>  				 1, 1, name, true);
>  	if (IS_ERR(vdev))
>  		return PTR_ERR(vdev);
> @@ -2022,7 +2028,6 @@ static int vduse_dev_init_vdpa(struct vduse_dev *dev, const char *name)
>  		put_device(&vdev->vdpa.dev);
>  		return ret;
>  	}
> -	set_dma_ops(&vdev->vdpa.dev, &vduse_dev_dma_ops);
>  	vdev->vdpa.map_token = &vdev->vdpa.dev;
>  	vdev->vdpa.mdev = &vduse_mgmt->mgmt_dev;
>  
> -- 
> 2.47.3