On Fri, 18 Jul 2025 17:16:13 +0800, Jason Wang <jasow...@redhat.com> wrote:
> This patch introduces map operations for virtio device. Virtio use to
> use DMA API which is not necessarily the case since some devices
> doesn't do DMA. Instead of using tricks and abusing DMA API, let's
> simply abstract the current mapping logic into a virtio specific
> mapping operations. For the device or transport that doesn't do DMA,
> they can implement their own mapping logic without the need to trick
> DMA core. In this case the map_token is opaque to the virtio core that
> will be passed back to the transport or device specific map
> operations. For other devices, DMA API will still be used, so map
> token will still be the dma device to minimize the changeset and
> performance impact.
>
> The mapping operations are abstract as a independent structure instead
> of reusing virtio_config_ops. This allows the transport can simply
> reuse the structure for lower layers.
>
> A set of new mapping helpers were introduced for the device that want
> to do mapping by themselves.
>
> Reviewed-by: Christoph Hellwig <h...@lst.de>
> Signed-off-by: Jason Wang <jasow...@redhat.com>
> ---
> drivers/virtio/virtio_ring.c | 174 +++++++++++++++++++++++++++++-----
> include/linux/virtio.h | 22 +++++
> include/linux/virtio_config.h | 68 +++++++++++++
> 3 files changed, 238 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
> index 26ce8a3d6927..3f86e74dd79f 100644
> --- a/drivers/virtio/virtio_ring.c
> +++ b/drivers/virtio/virtio_ring.c
> @@ -298,8 +298,14 @@ size_t virtio_max_dma_size(const struct virtio_device
> *vdev)
> {
> size_t max_segment_size = SIZE_MAX;
>
> - if (vring_use_map_api(vdev))
> - max_segment_size = dma_max_mapping_size(vdev->dev.parent);
> + if (vring_use_map_api(vdev)) {
> + if (vdev->map)
> + max_segment_size =
> + vdev->map->max_mapping_size(vdev->dev.parent);
> + else
> + max_segment_size =
> + dma_max_mapping_size(vdev->dev.parent);
> + }
>
> return max_segment_size;
> }
> @@ -310,8 +316,8 @@ static void *vring_alloc_queue(struct virtio_device
> *vdev, size_t size,
> void *map_token)
> {
> if (vring_use_map_api(vdev)) {
> - return dma_alloc_coherent(map_token, size,
> - map_handle, flag);
> + return virtqueue_map_alloc_coherent(vdev, map_token, size,
> + map_handle, flag);
> } else {
> void *queue = alloc_pages_exact(PAGE_ALIGN(size), flag);
>
> @@ -344,7 +350,8 @@ static void vring_free_queue(struct virtio_device *vdev,
> size_t size,
> void *map_token)
> {
> if (vring_use_map_api(vdev))
> - dma_free_coherent(map_token, size, queue, map_handle);
> + virtqueue_map_free_coherent(vdev, map_token, size,
> + queue, map_handle);
> else
> free_pages_exact(queue, PAGE_ALIGN(size));
> }
> @@ -388,9 +395,9 @@ static int vring_map_one_sg(const struct vring_virtqueue
> *vq, struct scatterlist
> * the way it expects (we don't guarantee that the scatterlist
> * will exist for the lifetime of the mapping).
> */
> - *addr = dma_map_page(vring_map_token(vq),
> - sg_page(sg), sg->offset, sg->length,
> - direction);
> + *addr = virtqueue_map_page_attrs(&vq->vq, sg_page(sg),
> + sg->offset, sg->length,
> + direction, 0);
>
> if (dma_mapping_error(vring_map_token(vq), *addr))
> return -ENOMEM;
> @@ -454,11 +461,12 @@ static unsigned int vring_unmap_one_split(const struct
> vring_virtqueue *vq,
> } else if (!vring_need_unmap_buffer(vq, extra))
> goto out;
>
> - dma_unmap_page(vring_map_token(vq),
> - extra->addr,
> - extra->len,
> - (flags & VRING_DESC_F_WRITE) ?
> - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> + virtqueue_unmap_page_attrs(&vq->vq,
> + extra->addr,
> + extra->len,
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + 0);
>
> out:
> return extra->next;
> @@ -1271,10 +1279,11 @@ static void vring_unmap_extra_packed(const struct
> vring_virtqueue *vq,
> } else if (!vring_need_unmap_buffer(vq, extra))
> return;
>
> - dma_unmap_page(vring_map_token(vq),
> - extra->addr, extra->len,
> - (flags & VRING_DESC_F_WRITE) ?
> - DMA_FROM_DEVICE : DMA_TO_DEVICE);
> + virtqueue_unmap_page_attrs(&vq->vq,
> + extra->addr, extra->len,
> + (flags & VRING_DESC_F_WRITE) ?
> + DMA_FROM_DEVICE : DMA_TO_DEVICE,
> + 0);
> }
>
> static struct vring_packed_desc *alloc_indirect_packed(unsigned int total_sg,
> @@ -3121,6 +3130,105 @@ const struct vring *virtqueue_get_vring(const struct
> virtqueue *vq)
> }
> EXPORT_SYMBOL_GPL(virtqueue_get_vring);
>
> +/**
> + * virtqueue_map_alloc_coherent - alloc coherent mapping
> + * @vdev: the virtio device we are talking to
> + * @token: device specific mapping token
> + * @size: the size of the buffer
> + * @map_handle: the pointer to the mapped adress
> + * @gfp: allocation flag (GFP_XXX)
> + *
> + * return virtual address or NULL on error
> + */
> +void *virtqueue_map_alloc_coherent(struct virtio_device *vdev,
> + void *map_token, size_t size,
> + dma_addr_t *map_handle, gfp_t gfp)
> +{
> + if (vdev->map)
> + return vdev->map->alloc(map_token, size, map_handle, gfp);
> + else
> + return dma_alloc_coherent(map_token, size,
> + map_handle, gfp);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_map_alloc_coherent);
> +
> +/**
> + * virtqueue_map_free_coherent - free coherent mapping
> + * @vdev: the virtio device we are talking to
> + * @token: device specific mapping token
> + * @size: the size of the buffer
> + * @map_handle: the mapped address that needs to be freed
> + *
> + */
> +void virtqueue_map_free_coherent(struct virtio_device *vdev,
> + void *map_token, size_t size, void *vaddr,
> + dma_addr_t map_handle)
> +{
> + if (vdev->map)
> + vdev->map->free(map_token, size, vaddr, map_handle, 0);
> + else
> + dma_free_coherent(map_token, size, vaddr, map_handle);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_map_free_coherent);
> +
> +/**
> + * virtqueue_map_page_attrs - map a page to the device
> + * @_vq: the virtqueue we are talking to
> + * @page: the page that will be mapped by the device
> + * @offset: the offset in the page for a buffer
> + * @size: the buffer size
> + * @dir: mapping direction
> + * @attrs: mapping attributes
> + *
> + * Returns mapped address. Caller should check that by
> virtqueue_mapping_error().
> + */
> +dma_addr_t virtqueue_map_page_attrs(const struct virtqueue *_vq,
> + struct page *page,
> + unsigned long offset,
> + size_t size,
> + enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + const struct vring_virtqueue *vq = to_vvq(_vq);
> + struct virtio_device *vdev = _vq->vdev;
> + void *map_token = vring_map_token(vq);
> +
> + if (vdev->map)
> + return vdev->map->map_page(map_token,
> + page, offset, size,
> + dir, attrs);
> +
> + return dma_map_page_attrs(map_token,
> + page, offset, size,
> + dir, attrs);
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_map_page_attrs);
> +
> +/**
> + * virtqueue_unmap_page_attrs - map a page to the device
> + * @_vq: the virtqueue we are talking to
> + * @map_handle: the mapped address
> + * @size: the buffer size
> + * @dir: mapping direction
> + * @attrs: unmapping attributes
> + */
> +void virtqueue_unmap_page_attrs(const struct virtqueue *_vq,
> + dma_addr_t map_handle,
> + size_t size, enum dma_data_direction dir,
> + unsigned long attrs)
> +{
> + const struct vring_virtqueue *vq = to_vvq(_vq);
> + struct virtio_device *vdev = _vq->vdev;
> + void *map_token = vring_map_token(vq);
> +
> + if (vdev->map)
> + vdev->map->unmap_page(map_token, map_handle,
> + size, dir, attrs);
> + else
> + dma_unmap_page_attrs(map_token, map_handle, size, dir, attrs);
How about setting dma_unmap_page_attrs as the default value of
vdev->map->unmap_page?
Then we can call vdev->map->unmap_page directly.
Thanks.
> +}
> +EXPORT_SYMBOL_GPL(virtqueue_unmap_page_attrs);
> +
> /**
> * virtqueue_map_single_attrs - map DMA for _vq
> * @_vq: the struct virtqueue we're talking about.
> @@ -3132,7 +3240,7 @@ EXPORT_SYMBOL_GPL(virtqueue_get_vring);
> * The caller calls this to do dma mapping in advance. The DMA address can be
> * passed to this _vq when it is in pre-mapped mode.
> *
> - * return DMA address. Caller should check that by virtqueue_mapping_error().
> + * return mapped address. Caller should check that by
> virtqueue_mapping_error().
> */
> dma_addr_t virtqueue_map_single_attrs(const struct virtqueue *_vq, void *ptr,
> size_t size,
> @@ -3151,8 +3259,8 @@ dma_addr_t virtqueue_map_single_attrs(const struct
> virtqueue *_vq, void *ptr,
> "rejecting DMA map of vmalloc memory\n"))
> return DMA_MAPPING_ERROR;
>
> - return dma_map_page_attrs(vring_map_token(vq), virt_to_page(ptr),
> - offset_in_page(ptr), size, dir, attrs);
> + return virtqueue_map_page_attrs(&vq->vq, virt_to_page(ptr),
> + offset_in_page(ptr), size, dir, attrs);
> }
> EXPORT_SYMBOL_GPL(virtqueue_map_single_attrs);
>
> @@ -3177,7 +3285,7 @@ void virtqueue_unmap_single_attrs(const struct
> virtqueue *_vq,
> if (!vq->use_map_api)
> return;
>
> - dma_unmap_page_attrs(vring_map_token(vq), addr, size, dir, attrs);
> + virtqueue_unmap_page_attrs(_vq, addr, size, dir, attrs);
> }
> EXPORT_SYMBOL_GPL(virtqueue_unmap_single_attrs);
>
> @@ -3212,11 +3320,16 @@ EXPORT_SYMBOL_GPL(virtqueue_map_mapping_error);
> bool virtqueue_map_need_sync(const struct virtqueue *_vq, dma_addr_t addr)
> {
> const struct vring_virtqueue *vq = to_vvq(_vq);
> + struct virtio_device *vdev = _vq->vdev;
> + void *token = vring_map_token(vq);
>
> if (!vq->use_map_api)
> return false;
>
> - return dma_need_sync(vring_map_token(vq), addr);
> + if (vdev->map)
> + return vdev->map->need_sync(token, addr);
> + else
> + return dma_need_sync(token, addr);
> }
> EXPORT_SYMBOL_GPL(virtqueue_map_need_sync);
>
> @@ -3238,12 +3351,16 @@ void virtqueue_map_sync_single_range_for_cpu(const
> struct virtqueue *_vq,
> enum dma_data_direction dir)
> {
> const struct vring_virtqueue *vq = to_vvq(_vq);
> - struct device *dev = vring_map_token(vq);
> + struct virtio_device *vdev = _vq->vdev;
> + void *token = vring_map_token(vq);
>
> if (!vq->use_map_api)
> return;
>
> - dma_sync_single_range_for_cpu(dev, addr, offset, size, dir);
> + if (vdev->map)
> + vdev->map->sync_single_for_cpu(token, addr + offset, size, dir);
> + else
> + dma_sync_single_range_for_cpu(token, addr, offset, size, dir);
> }
> EXPORT_SYMBOL_GPL(virtqueue_map_sync_single_range_for_cpu);
>
> @@ -3264,12 +3381,17 @@ void virtqueue_map_sync_single_range_for_device(const
> struct virtqueue *_vq,
> enum dma_data_direction dir)
> {
> const struct vring_virtqueue *vq = to_vvq(_vq);
> - struct device *dev = vring_map_token(vq);
> + struct virtio_device *vdev = _vq->vdev;
> + void *token = vring_map_token(vq);
>
> if (!vq->use_map_api)
> return;
>
> - dma_sync_single_range_for_device(dev, addr, offset, size, dir);
> + if (vdev->map)
> + vdev->map->sync_single_for_device(token, addr + offset,
> + size, dir);
> + else
> + dma_sync_single_range_for_device(token, addr, offset, size,
> dir);
> }
> EXPORT_SYMBOL_GPL(virtqueue_map_sync_single_range_for_device);
>
> diff --git a/include/linux/virtio.h b/include/linux/virtio.h
> index 88de0e368e01..d252939d83dc 100644
> --- a/include/linux/virtio.h
> +++ b/include/linux/virtio.h
> @@ -159,6 +159,7 @@ struct virtio_device {
> struct virtio_device_id id;
> const struct virtio_config_ops *config;
> const struct vringh_config_ops *vringh_config;
> + const struct virtio_map_ops *map;
> struct list_head vqs;
> u64 features;
> void *priv;
> @@ -264,6 +265,27 @@ void unregister_virtio_driver(struct virtio_driver *drv);
> module_driver(__virtio_driver, register_virtio_driver, \
> unregister_virtio_driver)
>
> +
> +void *virtqueue_map_alloc_coherent(struct virtio_device *vdev,
> + void *map_token, size_t size,
> + dma_addr_t *dma_handle, gfp_t gfp);
> +
> +void virtqueue_map_free_coherent(struct virtio_device *vdev,
> + void *map_token, size_t size, void *vaddr,
> + dma_addr_t dma_handle);
> +
> +dma_addr_t virtqueue_map_page_attrs(const struct virtqueue *_vq,
> + struct page *page,
> + unsigned long offset,
> + size_t size,
> + enum dma_data_direction dir,
> + unsigned long attrs);
> +
> +void virtqueue_unmap_page_attrs(const struct virtqueue *_vq,
> + dma_addr_t dma_handle,
> + size_t size, enum dma_data_direction dir,
> + unsigned long attrs);
> +
> dma_addr_t virtqueue_map_single_attrs(const struct virtqueue *_vq, void
> *ptr, size_t size,
> enum dma_data_direction dir, unsigned
> long attrs);
> void virtqueue_unmap_single_attrs(const struct virtqueue *_vq, dma_addr_t
> addr,
> diff --git a/include/linux/virtio_config.h b/include/linux/virtio_config.h
> index 861198a74be2..b4f31afa0726 100644
> --- a/include/linux/virtio_config.h
> +++ b/include/linux/virtio_config.h
> @@ -139,6 +139,74 @@ struct virtio_config_ops {
> int (*enable_vq_after_reset)(struct virtqueue *vq);
> };
>
> +/**
> + * struct virtio_map_ops - operations for mapping buffer for a virtio device
> + * Note: For transport that has its own mapping logic it must
> + * implements all of the operations
> + * @map_page: map a buffer to the device
> + * token: device specific mapping token
> + * page: the page that will be mapped by the device
> + * offset: the offset in the page for a buffer
> + * size: the buffer size
> + * dir: mapping direction
> + * attrs: mapping attributes
> + * Returns: the mapped address
> + * @unmap_page: unmap a buffer from the device
> + * token: device specific mapping token
> + * map_handle: the mapped address
> + * size: the buffer size
> + * dir: mapping direction
> + * attrs: unmapping attributes
> + * @sync_single_for_cpu: sync a single buffer from device to cpu
> + * token: device specific mapping token
> + * map_handle: the mapping adress to sync
> + * size: the size of the buffer
> + * dir: synchronization direction
> + * @sync_single_for_device: sync a single buffer from cpu to device
> + * token: device specific mapping token
> + * map_handle: the mapping adress to sync
> + * size: the size of the buffer
> + * dir: synchronization direction
> + * @alloc: alloc a coherent buffer mapping
> + * token: device specific mapping token
> + * size: the size of the buffer
> + * map_handle: the mapping adress to sync
> + * gfp: allocation flag (GFP_XXX)
> + * Returns: virtual address of the allocated buffer
> + * @free: free a coherent buffer mapping
> + * token: device specific mapping token
> + * size: the size of the buffer
> + * vaddr: virtual address of the buffer
> + * map_handle: the mapping adress to sync
> + * attrs: unmapping attributes
> + * @need_sync: if the buffer needs synchronization
> + * token: device specific mapping token
> + * map_handle: the mapped address
> + * Returns: whether the buffer needs synchronization
> + * @max_mapping_size: get the maximum buffer size that can be mapped
> + * token: device specific mapping token
> + * Returns: the maximum buffer size that can be mapped
> + */
> +struct virtio_map_ops {
> + dma_addr_t (*map_page)(void *token, struct page *page,
> + unsigned long offset, size_t size,
> + enum dma_data_direction dir, unsigned long
> attrs);
> + void (*unmap_page)(void *token, dma_addr_t map_handle,
> + size_t size, enum dma_data_direction dir,
> + unsigned long attrs);
> + void (*sync_single_for_cpu)(void *token, dma_addr_t map_handle,
> + size_t size, enum dma_data_direction dir);
> + void (*sync_single_for_device)(void *token,
> + dma_addr_t map_handle, size_t size,
> + enum dma_data_direction dir);
> + void *(*alloc)(void *token, size_t size,
> + dma_addr_t *map_handle, gfp_t gfp);
> + void (*free)(void *token, size_t size, void *vaddr,
> + dma_addr_t map_handle, unsigned long attrs);
> + bool (*need_sync)(void *token, dma_addr_t map_handle);
> + size_t (*max_mapping_size)(void *token);
> +};
> +
> /* If driver didn't advertise the feature, it will never appear. */
> void virtio_check_driver_offered_feature(const struct virtio_device *vdev,
> unsigned int fbit);
> --
> 2.47.3
>
