Re: [PATCH v2 02/12] virtio: drop the sync operations from virtio_map_ops

[Eugenio Perez Martin]

On Tue, Aug 18, 2026 at 11:14 PM Alexander Graf <graf@xxxxxxxxxx> wrote:
>
> With the map sync API gone, sync_single_for_cpu, sync_single_for_device
> and need_sync in struct virtio_map_ops are members the virtqueue never
> calls. vduse is the only implementation in the tree and provides all
> three, and the next implementer has to decide what to put in them.
>
> Drop the three members and their kernel-doc, and remove the vduse
> functions that provided them. vduse_domain_bounce() stays, because
> vduse_domain_map_page() and vduse_domain_unmap_page() bounce through it
> as well. That way the struct asks an implementation for six operations
> instead of nine.
>
> Suggested-by: Michael S. Tsirkin <mst@xxxxxxxxxx>

Acked-by: Eugenio Pérez <eperezma@xxxxxxxxxx>

> Assisted-by: Kiro:claude-opus-5 checkpatch
> Signed-off-by: Alexander Graf <graf@xxxxxxxxxx>
> ---
>  drivers/vdpa/vdpa_user/iova_domain.c | 20 --------------
>  drivers/vdpa/vdpa_user/iova_domain.h |  8 ------
>  drivers/vdpa/vdpa_user/vduse_dev.c   | 40 ----------------------------
>  include/linux/virtio_config.h        | 20 --------------
>  4 files changed, 88 deletions(-)
>
> diff --git a/drivers/vdpa/vdpa_user/iova_domain.c b/drivers/vdpa/vdpa_user/iova_domain.c
> index 4dc76c0d0d13..094fe1ec02c3 100644
> --- a/drivers/vdpa/vdpa_user/iova_domain.c
> +++ b/drivers/vdpa/vdpa_user/iova_domain.c
> @@ -424,26 +424,6 @@ static void vduse_domain_free_iova(struct iova_domain *iovad,
>         free_iova_fast(iovad, iova >> shift, iova_len);
>  }
>
> -void vduse_domain_sync_single_for_device(struct vduse_iova_domain *domain,
> -                                     dma_addr_t dma_addr, size_t size,
> -                                     enum dma_data_direction dir)
> -{
> -       read_lock(&domain->bounce_lock);
> -       if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
> -               vduse_domain_bounce(domain, dma_addr, size, DMA_TO_DEVICE);
> -       read_unlock(&domain->bounce_lock);
> -}
> -
> -void vduse_domain_sync_single_for_cpu(struct vduse_iova_domain *domain,
> -                                     dma_addr_t dma_addr, size_t size,
> -                                     enum dma_data_direction dir)
> -{
> -       read_lock(&domain->bounce_lock);
> -       if (dir == DMA_FROM_DEVICE || dir == DMA_BIDIRECTIONAL)
> -               vduse_domain_bounce(domain, dma_addr, size, DMA_FROM_DEVICE);
> -       read_unlock(&domain->bounce_lock);
> -}
> -
>  dma_addr_t vduse_domain_map_page(struct vduse_iova_domain *domain,
>                                  struct page *page, unsigned long offset,
>                                  size_t size, enum dma_data_direction dir,
> diff --git a/drivers/vdpa/vdpa_user/iova_domain.h b/drivers/vdpa/vdpa_user/iova_domain.h
> index e50e55d1396f..66f14764a5db 100644
> --- a/drivers/vdpa/vdpa_user/iova_domain.h
> +++ b/drivers/vdpa/vdpa_user/iova_domain.h
> @@ -48,14 +48,6 @@ int vduse_domain_set_map(struct vduse_iova_domain *domain,
>  void vduse_domain_clear_map(struct vduse_iova_domain *domain,
>                             struct vhost_iotlb *iotlb);
>
> -void vduse_domain_sync_single_for_device(struct vduse_iova_domain *domain,
> -                                     dma_addr_t dma_addr, size_t size,
> -                                     enum dma_data_direction dir);
> -
> -void vduse_domain_sync_single_for_cpu(struct vduse_iova_domain *domain,
> -                                     dma_addr_t dma_addr, size_t size,
> -                                     enum dma_data_direction dir);
> -
>  dma_addr_t vduse_domain_map_page(struct vduse_iova_domain *domain,
>                                  struct page *page, unsigned long offset,
>                                  size_t size, enum dma_data_direction dir,
> diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c b/drivers/vdpa/vdpa_user/vduse_dev.c
> index 10dcf016bfb0..7a1a344539b8 100644
> --- a/drivers/vdpa/vdpa_user/vduse_dev.c
> +++ b/drivers/vdpa/vdpa_user/vduse_dev.c
> @@ -932,34 +932,6 @@ static const struct vdpa_config_ops vduse_vdpa_config_ops = {
>         .free                   = vduse_vdpa_free,
>  };
>
> -static void vduse_dev_sync_single_for_device(union virtio_map token,
> -                                            dma_addr_t dma_addr, size_t size,
> -                                            enum dma_data_direction dir)
> -{
> -       struct vduse_iova_domain *domain;
> -
> -       if (!token.group)
> -               return;
> -
> -       guard(vq_group_as_read_lock)(token.group);
> -       domain = token.group->as->domain;
> -       vduse_domain_sync_single_for_device(domain, dma_addr, size, dir);
> -}
> -
> -static void vduse_dev_sync_single_for_cpu(union virtio_map token,
> -                                            dma_addr_t dma_addr, size_t size,
> -                                            enum dma_data_direction dir)
> -{
> -       struct vduse_iova_domain *domain;
> -
> -       if (!token.group)
> -               return;
> -
> -       guard(vq_group_as_read_lock)(token.group);
> -       domain = token.group->as->domain;
> -       vduse_domain_sync_single_for_cpu(domain, dma_addr, size, dir);
> -}
> -
>  static dma_addr_t vduse_dev_map_page(union virtio_map token, struct page *page,
>                                      unsigned long offset, size_t size,
>                                      enum dma_data_direction dir,
> @@ -1037,15 +1009,6 @@ static void vduse_dev_free_coherent(union virtio_map token, size_t size,
>         free_pages_exact(vaddr, size);
>  }
>
> -static bool vduse_dev_need_sync(union virtio_map token, dma_addr_t dma_addr)
> -{
> -       if (!token.group)
> -               return false;
> -
> -       guard(vq_group_as_read_lock)(token.group);
> -       return dma_addr < token.group->as->domain->bounce_size;
> -}
> -
>  static int vduse_dev_mapping_error(union virtio_map token, dma_addr_t dma_addr)
>  {
>         if (unlikely(dma_addr == DMA_MAPPING_ERROR))
> @@ -1063,13 +1026,10 @@ static size_t vduse_dev_max_mapping_size(union virtio_map token)
>  }
>
>  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,
>         .unmap_page = vduse_dev_unmap_page,
>         .alloc = vduse_dev_alloc_coherent,
>         .free = vduse_dev_free_coherent,
> -       .need_sync = vduse_dev_need_sync,
>         .mapping_error = vduse_dev_mapping_error,
>         .max_mapping_size = vduse_dev_max_mapping_size,
>  };
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 69f84ea85d71..eb38c876a628 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -157,16 +157,6 @@ struct virtio_config_ops {
>   *      size: the buffer size
>   *      dir: mapping direction
>   *      attrs: unmapping attributes
> - * @sync_single_for_cpu: sync a single buffer from device to cpu
> - *      map: metadata for performing mapping
> - *      map_handle: the mapping address to sync
> - *      size: the size of the buffer
> - *      dir: synchronization direction
> - * @sync_single_for_device: sync a single buffer from cpu to device
> - *      map: metadata for performing mapping
> - *      map_handle: the mapping address to sync
> - *      size: the size of the buffer
> - *      dir: synchronization direction
>   * @alloc: alloc a coherent buffer mapping
>   *      map: metadata for performing mapping
>   *      size: the size of the buffer
> @@ -179,10 +169,6 @@ struct virtio_config_ops {
>   *      vaddr: virtual address of the buffer
>   *      map_handle: the mapping address that needs to be freed
>   *      attrs: unmapping attributes
> - * @need_sync: if the buffer needs synchronization
> - *      map: metadata for performing mapping
> - *      map_handle: the mapped address
> - *      Returns whether the buffer needs synchronization
>   * @mapping_error: if the mapping address is error
>   *      map: metadata for performing mapping
>   *      map_handle: the mapped address
> @@ -197,16 +183,10 @@ struct virtio_map_ops {
>         void (*unmap_page)(union virtio_map map, dma_addr_t map_handle,
>                            size_t size, enum dma_data_direction dir,
>                            unsigned long attrs);
> -       void (*sync_single_for_cpu)(union virtio_map map, dma_addr_t map_handle,
> -                                   size_t size, enum dma_data_direction dir);
> -       void (*sync_single_for_device)(union virtio_map map,
> -                                      dma_addr_t map_handle, size_t size,
> -                                      enum dma_data_direction dir);
>         void *(*alloc)(union virtio_map map, size_t size,
>                        dma_addr_t *map_handle, gfp_t gfp);
>         void (*free)(union virtio_map map, size_t size, void *vaddr,
>                      dma_addr_t map_handle, unsigned long attrs);
> -       bool (*need_sync)(union virtio_map map, dma_addr_t map_handle);
>         int (*mapping_error)(union virtio_map map, dma_addr_t map_handle);
>         size_t (*max_mapping_size)(union virtio_map map);
>  };
>