Re: [PATCH bpf-next v4 01/11] xsk: Support tx_metadata_len

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On Thu, 19 Oct 2023 at 19:50, Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
>
> For zerocopy mode, tx_desc->addr can point to the arbitrary offset

nit: the -> an

> and carry some TX metadata in the headroom. For copy mode, there
> is no way currently to populate skb metadata.
>
> Introduce new tx_metadata_len umem config option that indicates how many
> bytes to treat as metadata. Metadata bytes come prior to tx_desc address
> (same as in RX case).
>
> The size of the metadata has the same constraints as XDP:
> - less than 256 bytes
> - 4-byte aligned
> - non-zero
>
> This data is not interpreted in any way right now.
>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> ---
>  include/net/xdp_sock.h            |  1 +
>  include/net/xsk_buff_pool.h       |  1 +
>  include/uapi/linux/if_xdp.h       |  1 +
>  net/xdp/xdp_umem.c                |  4 ++++
>  net/xdp/xsk.c                     | 12 +++++++++++-
>  net/xdp/xsk_buff_pool.c           |  1 +
>  net/xdp/xsk_queue.h               | 17 ++++++++++-------
>  tools/include/uapi/linux/if_xdp.h |  1 +
>  8 files changed, 30 insertions(+), 8 deletions(-)
>
> diff --git a/include/net/xdp_sock.h b/include/net/xdp_sock.h
> index 7dd0df2f6f8e..5ae88a00f34a 100644
> --- a/include/net/xdp_sock.h
> +++ b/include/net/xdp_sock.h
> @@ -30,6 +30,7 @@ struct xdp_umem {
>         struct user_struct *user;
>         refcount_t users;
>         u8 flags;
> +       u8 tx_metadata_len;
>         bool zc;
>         struct page **pgs;
>         int id;
> diff --git a/include/net/xsk_buff_pool.h b/include/net/xsk_buff_pool.h
> index b0bdff26fc88..1985ffaf9b0c 100644
> --- a/include/net/xsk_buff_pool.h
> +++ b/include/net/xsk_buff_pool.h
> @@ -77,6 +77,7 @@ struct xsk_buff_pool {
>         u32 chunk_size;
>         u32 chunk_shift;
>         u32 frame_len;
> +       u8 tx_metadata_len; /* inherited from umem */
>         u8 cached_need_wakeup;
>         bool uses_need_wakeup;
>         bool dma_need_sync;
> diff --git a/include/uapi/linux/if_xdp.h b/include/uapi/linux/if_xdp.h
> index 8d48863472b9..2ecf79282c26 100644
> --- a/include/uapi/linux/if_xdp.h
> +++ b/include/uapi/linux/if_xdp.h
> @@ -76,6 +76,7 @@ struct xdp_umem_reg {
>         __u32 chunk_size;
>         __u32 headroom;
>         __u32 flags;
> +       __u32 tx_metadata_len;
>  };
>
>  struct xdp_statistics {
> diff --git a/net/xdp/xdp_umem.c b/net/xdp/xdp_umem.c
> index 06cead2b8e34..333f3d53aad4 100644
> --- a/net/xdp/xdp_umem.c
> +++ b/net/xdp/xdp_umem.c
> @@ -199,6 +199,9 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
>         if (headroom >= chunk_size - XDP_PACKET_HEADROOM)
>                 return -EINVAL;
>
> +       if (mr->tx_metadata_len > 256 || mr->tx_metadata_len % 4)
> +               return -EINVAL;

Should be >= 256 since the final internal destination is a u8 and the
documentation says "should be less than 256 bytes".

> +
>         umem->size = size;
>         umem->headroom = headroom;
>         umem->chunk_size = chunk_size;
> @@ -207,6 +210,7 @@ static int xdp_umem_reg(struct xdp_umem *umem, struct xdp_umem_reg *mr)
>         umem->pgs = NULL;
>         umem->user = NULL;
>         umem->flags = mr->flags;
> +       umem->tx_metadata_len = mr->tx_metadata_len;
>
>         INIT_LIST_HEAD(&umem->xsk_dma_list);
>         refcount_set(&umem->users, 1);
> diff --git a/net/xdp/xsk.c b/net/xdp/xsk.c
> index ba070fd37d24..ba4c77a24a83 100644
> --- a/net/xdp/xsk.c
> +++ b/net/xdp/xsk.c
> @@ -1265,6 +1265,14 @@ struct xdp_umem_reg_v1 {
>         __u32 headroom;
>  };
>
> +struct xdp_umem_reg_v2 {
> +       __u64 addr; /* Start of packet data area */
> +       __u64 len; /* Length of packet data area */
> +       __u32 chunk_size;
> +       __u32 headroom;
> +       __u32 flags;
> +};
> +
>  static int xsk_setsockopt(struct socket *sock, int level, int optname,
>                           sockptr_t optval, unsigned int optlen)
>  {
> @@ -1308,8 +1316,10 @@ static int xsk_setsockopt(struct socket *sock, int level, int optname,
>
>                 if (optlen < sizeof(struct xdp_umem_reg_v1))
>                         return -EINVAL;
> -               else if (optlen < sizeof(mr))
> +               else if (optlen < sizeof(struct xdp_umem_reg_v2))
>                         mr_size = sizeof(struct xdp_umem_reg_v1);
> +               else if (optlen < sizeof(mr))
> +                       mr_size = sizeof(struct xdp_umem_reg_v2);
>
>                 if (copy_from_sockptr(&mr, optval, mr_size))
>                         return -EFAULT;
> diff --git a/net/xdp/xsk_buff_pool.c b/net/xdp/xsk_buff_pool.c
> index 49cb9f9a09be..386eddcdf837 100644
> --- a/net/xdp/xsk_buff_pool.c
> +++ b/net/xdp/xsk_buff_pool.c
> @@ -85,6 +85,7 @@ struct xsk_buff_pool *xp_create_and_assign_umem(struct xdp_sock *xs,
>                 XDP_PACKET_HEADROOM;
>         pool->umem = umem;
>         pool->addrs = umem->addrs;
> +       pool->tx_metadata_len = umem->tx_metadata_len;
>         INIT_LIST_HEAD(&pool->free_list);
>         INIT_LIST_HEAD(&pool->xskb_list);
>         INIT_LIST_HEAD(&pool->xsk_tx_list);
> diff --git a/net/xdp/xsk_queue.h b/net/xdp/xsk_queue.h
> index 13354a1e4280..c74a1372bcb9 100644
> --- a/net/xdp/xsk_queue.h
> +++ b/net/xdp/xsk_queue.h
> @@ -143,15 +143,17 @@ static inline bool xp_unused_options_set(u32 options)
>  static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
>                                             struct xdp_desc *desc)
>  {
> -       u64 offset = desc->addr & (pool->chunk_size - 1);
> +       u64 addr = desc->addr - pool->tx_metadata_len;
> +       u64 len = desc->len + pool->tx_metadata_len;
> +       u64 offset = addr & (pool->chunk_size - 1);
>
>         if (!desc->len)
>                 return false;
>
> -       if (offset + desc->len > pool->chunk_size)
> +       if (offset + len > pool->chunk_size)
>                 return false;
>
> -       if (desc->addr >= pool->addrs_cnt)
> +       if (addr >= pool->addrs_cnt)
>                 return false;
>
>         if (xp_unused_options_set(desc->options))
> @@ -162,16 +164,17 @@ static inline bool xp_aligned_validate_desc(struct xsk_buff_pool *pool,
>  static inline bool xp_unaligned_validate_desc(struct xsk_buff_pool *pool,
>                                               struct xdp_desc *desc)
>  {
> -       u64 addr = xp_unaligned_add_offset_to_addr(desc->addr);
> +       u64 addr = xp_unaligned_add_offset_to_addr(desc->addr) - pool->tx_metadata_len;
> +       u64 len = desc->len + pool->tx_metadata_len;
>
>         if (!desc->len)
>                 return false;
>
> -       if (desc->len > pool->chunk_size)
> +       if (len > pool->chunk_size)
>                 return false;
>
> -       if (addr >= pool->addrs_cnt || addr + desc->len > pool->addrs_cnt ||
> -           xp_desc_crosses_non_contig_pg(pool, addr, desc->len))
> +       if (addr >= pool->addrs_cnt || addr + len > pool->addrs_cnt ||
> +           xp_desc_crosses_non_contig_pg(pool, addr, len))
>                 return false;
>
>         if (xp_unused_options_set(desc->options))
> diff --git a/tools/include/uapi/linux/if_xdp.h b/tools/include/uapi/linux/if_xdp.h
> index 73a47da885dc..34411a2e5b6c 100644
> --- a/tools/include/uapi/linux/if_xdp.h
> +++ b/tools/include/uapi/linux/if_xdp.h
> @@ -76,6 +76,7 @@ struct xdp_umem_reg {
>         __u32 chunk_size;
>         __u32 headroom;
>         __u32 flags;
> +       __u32 tx_metadata_len;
>  };
>
>  struct xdp_statistics {
> --
> 2.42.0.655.g421f12c284-goog
>
>




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