Re: [PATCH net-next v12 03/13] netdev: support binding dma-buf to netdevice

Pavel Begunkov
2024-06-17T13:22:46Z

On 6/13/24 02:35, Mina Almasry wrote:
> Add a netdev_dmabuf_binding struct which represents the
> dma-buf-to-netdevice binding. The netlink API will bind the dma-buf to
> rx queues on the netdevice. On the binding, the dma_buf_attach
> & dma_buf_map_attachment will occur. The entries in the sg_table from
> mapping will be inserted into a genpool to make it ready
> for allocation.
>
> The chunks in the genpool are owned by a dmabuf_chunk_owner struct which
> holds the dma-buf offset of the base of the chunk and the dma_addr of
> the chunk. Both are needed to use allocations that come from this chunk.
>
> We create a new type that represents an allocation from the genpool:
> net_iov. We setup the net_iov allocation size in the
> genpool to PAGE_SIZE for simplicity: to match the PAGE_SIZE normally
> allocated by the page pool and given to the drivers.
>
> The user can unbind the dmabuf from the netdevice by closing the netlink
> socket that established the binding. We do this so that the binding is
> automatically unbound even if the userspace process crashes.
>
> The binding and unbinding leaves an indicator in struct netdev_rx_queue
> that the given queue is bound, but the binding doesn't take effect until
> the driver actually reconfigures its queues, and re-initializes its page
> pool.
>
> The netdev_dmabuf_binding struct is refcounted, and releases its
> resources only when all the refs are released.
>
> Signed-off-by: Willem de Bruijn <willemb@google.com>
> Signed-off-by: Kaiyuan Zhang <kaiyuanz@google.com>
> Signed-off-by: Mina Almasry <almasrymina@google.com>

Apart from the comment below

Reviewed-by: Pavel Begunkov <asml.silence@gmail.com> # excluding netlink

> diff --git a/include/net/devmem.h b/include/net/devmem.h
> new file mode 100644
> index 0000000000000..eaf3fd965d7a8
...
> diff --git a/net/core/dev.c b/net/core/dev.c
> index c361a7b69da86..84c9f96a6c9bf 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -158,6 +158,9 @@
> #include <net/page_pool/types.h>
> #include <net/page_pool/helpers.h>
> #include <net/rps.h>
> +#include <linux/genalloc.h>
> +#include <linux/dma-buf.h>
> +#include <net/devmem.h>
>
> #include "dev.h"
> #include "net-sysfs.h"
> diff --git a/net/core/devmem.c b/net/core/devmem.c
> new file mode 100644
> index 0000000000000..951a06004c430
> --- /dev/null
> +++ b/net/core/devmem.c
> @@ -0,0 +1,252 @@
> +// SPDX-License-Identifier: GPL-2.0-or-later
> +/*
> + * Devmem TCP
> + *
> + * Authors: Mina Almasry <almasrymina@google.com>
> + * Willem de Bruijn <willemdebruijn.kernel@gmail.com>
> + * Kaiyuan Zhang <kaiyuanz@google.com
> + */
> +
> +#include <linux/types.h>
> +#include <linux/mm.h>
> +#include <linux/netdevice.h>
> +#include <trace/events/page_pool.h>
> +#include <net/netdev_rx_queue.h>
> +#include <net/page_pool/types.h>
> +#include <net/page_pool/helpers.h>
> +#include <linux/genalloc.h>
> +#include <linux/dma-buf.h>
> +#include <net/devmem.h>
> +#include <net/netdev_queues.h>
> +
> +/* Device memory support */
> +
> +#if defined(CONFIG_DMA_SHARED_BUFFER) && defined(CONFIG_GENERIC_ALLOCATOR)
> +static void net_devmem_dmabuf_free_chunk_owner(struct gen_pool *genpool,
> + struct gen_pool_chunk *chunk,
> + void *not_used)
> +{
> + struct dmabuf_genpool_chunk_owner *owner = chunk->owner;
> +
> + kvfree(owner->niovs);
> + kfree(owner);
> +}
> +
> +void __net_devmem_dmabuf_binding_free(struct net_devmem_dmabuf_binding *binding)
> +{
> + size_t size, avail;
> +
> + gen_pool_for_each_chunk(binding->chunk_pool,
> + net_devmem_dmabuf_free_chunk_owner, NULL);
> +
> + size = gen_pool_size(binding->chunk_pool);
> + avail = gen_pool_avail(binding->chunk_pool);
> +
> + if (!WARN(size != avail, "can't destroy genpool. size=%zu, avail=%zu",
> + size, avail))
> + gen_pool_destroy(binding->chunk_pool);
> +
> + dma_buf_unmap_attachment(binding->attachment, binding->sgt,
> + DMA_FROM_DEVICE);

It's unmapped here as DMA_FROM_DEVICE, a fail path does DMA_BIDIRECTIONAL,
dma_buf_map_attachment() passes BIDIRECTIONAL.

> + dma_buf_detach(binding->dmabuf, binding->attachment);
> + dma_buf_put(binding->dmabuf);
> + xa_destroy(&binding->bound_rxq_list);
> + kfree(binding);
> +}
> +
> +/* Protected by rtnl_lock() */
> +static DEFINE_XARRAY_FLAGS(net_devmem_dmabuf_bindings, XA_FLAGS_ALLOC1);
> +
...

--
Pavel Begunkov