[xdp-hints] Re: [PATCH bpf-next v3 12/21] xdp: Add checksum hint

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Larysa Zaremba wrote:
> Implement functionality that enables drivers to expose to XDP code checksum
> information that consists of:
> 
> - Checksum status - bitfield that consists of
>   - number of consecutive validated checksums. This is almost the same as
>     csum_level in skb, but starts with 1. Enum names for those bits still
>     use checksum level concept, so it is less confusing for driver
>     developers.
>   - Is checksum partial? This bit cannot coexist with any other
>   - Is there a complete checksum available?
> - Additional checksum data, a union of:
>   - checksum start and offset, if checksum is partial
>   - complete checksum, if available
> 
> Signed-off-by: Larysa Zaremba <larysa.zaremba@intel.com>
> ---
>  Documentation/networking/xdp-rx-metadata.rst |  3 ++
>  include/linux/netdevice.h                    |  3 ++
>  include/net/xdp.h                            | 46 ++++++++++++++++++++
>  kernel/bpf/offload.c                         |  2 +
>  net/core/xdp.c                               | 23 ++++++++++
>  5 files changed, 77 insertions(+)
> 
> diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> index ea6dd79a21d3..7f056a44f682 100644
> --- a/Documentation/networking/xdp-rx-metadata.rst
> +++ b/Documentation/networking/xdp-rx-metadata.rst
> @@ -26,6 +26,9 @@ metadata is supported, this set will grow:
>  .. kernel-doc:: net/core/xdp.c
>     :identifiers: bpf_xdp_metadata_rx_vlan_tag
>  
> +.. kernel-doc:: net/core/xdp.c
> +   :identifiers: bpf_xdp_metadata_rx_csum
> +
>  An XDP program can use these kfuncs to read the metadata into stack
>  variables for its own consumption. Or, to pass the metadata on to other
>  consumers, an XDP program can store it into the metadata area carried
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index 1749f4f75c64..4f6da36ac123 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1660,6 +1660,9 @@ struct xdp_metadata_ops {
>  			       enum xdp_rss_hash_type *rss_type);
>  	int	(*xmo_rx_vlan_tag)(const struct xdp_md *ctx, u16 *vlan_tci,
>  				   __be16 *vlan_proto);
> +	int	(*xmo_rx_csum)(const struct xdp_md *ctx,
> +			       enum xdp_csum_status *csum_status,
> +			       union xdp_csum_info *csum_info);
>  };
>  
>  /**
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 89c58f56ffc6..2b7a7d678ff4 100644
> --- a/include/net/xdp.h
> +++ b/include/net/xdp.h
> @@ -391,6 +391,8 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
>  			   bpf_xdp_metadata_rx_hash) \
>  	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_VLAN_TAG, \
>  			   bpf_xdp_metadata_rx_vlan_tag) \
> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_CSUM, \
> +			   bpf_xdp_metadata_rx_csum) \
>  
>  enum {
>  #define XDP_METADATA_KFUNC(name, _) name,
> @@ -448,6 +450,50 @@ enum xdp_rss_hash_type {
>  	XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP | XDP_RSS_L3_DYNHDR,
>  };
>  
> +union xdp_csum_info {
> +	/* Checksum referred to by ``csum_start + csum_offset`` is considered
> +	 * valid, but was never calculated, TX device has to do this,
> +	 * starting from csum_start packet byte.
> +	 * Any preceding checksums are also considered valid.
> +	 * Available, if ``status == XDP_CHECKSUM_PARTIAL``.
> +	 */
> +	struct {
> +		u16 csum_start;
> +		u16 csum_offset;
> +	};
> +
> +	/* Checksum, calculated over the whole packet.
> +	 * Available, if ``status & XDP_CHECKSUM_COMPLETE``.
> +	 */
> +	u32 checksum;
> +};
> +
> +enum xdp_csum_status {
> +	/* HW had parsed several transport headers and validated their
> +	 * checksums, same as ``CHECKSUM_UNNECESSARY`` in ``sk_buff``.
> +	 * 3 least significat bytes contain number of consecutive checksum,

typo: significant

(I did not scan for typos, just came across this when trying to understand
the skb->csum_level + 1 trick. Probably good to run a spell check).

> +	 * starting with the outermost, reported by hardware as valid.
> +	 * ``sk_buff`` checksum level (``csum_level``) notation is provided
> +	 * for driver developers.
> +	 */
> +	XDP_CHECKSUM_VALID_LVL0		= 1,	/* 1 outermost checksum */
> +	XDP_CHECKSUM_VALID_LVL1		= 2,	/* 2 outermost checksums */
> +	XDP_CHECKSUM_VALID_LVL2		= 3,	/* 3 outermost checksums */
> +	XDP_CHECKSUM_VALID_LVL3		= 4,	/* 4 outermost checksums */
> +	XDP_CHECKSUM_VALID_NUM_MASK	= GENMASK(2, 0),
> +	XDP_CHECKSUM_VALID		= XDP_CHECKSUM_VALID_NUM_MASK,
> +
> +	/* Occurs if packet is sent virtually (between Linux VMs / containers)
> +	 * This status cannot coexist with any other.
> +	 * Refer to ``csum_start`` and ``csum_offset`` in ``xdp_csum_info``
> +	 * for more information.
> +	 */
> +	XDP_CHECKSUM_PARTIAL	= BIT(3),
> +
> +	/* Checksum, calculated over the entire packet is provided */
> +	XDP_CHECKSUM_COMPLETE	= BIT(4),
> +};
> +
>  #ifdef CONFIG_NET
>  u32 bpf_xdp_metadata_kfunc_id(int id);
>  bool bpf_dev_bound_kfunc_id(u32 btf_id);
> diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> index 986e7becfd42..f60a6add5273 100644
> --- a/kernel/bpf/offload.c
> +++ b/kernel/bpf/offload.c
> @@ -850,6 +850,8 @@ void *bpf_dev_bound_resolve_kfunc(struct bpf_prog *prog, u32 func_id)
>  		p = ops->xmo_rx_hash;
>  	else if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_VLAN_TAG))
>  		p = ops->xmo_rx_vlan_tag;
> +	else if (func_id == bpf_xdp_metadata_kfunc_id(XDP_METADATA_KFUNC_RX_CSUM))
> +		p = ops->xmo_rx_csum;
>  out:
>  	up_read(&bpf_devs_lock);
>  
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index 8b55419d332e..d4ea54046afc 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -772,6 +772,29 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx,
>  	return -EOPNOTSUPP;
>  }
>  
> +/**
> + * bpf_xdp_metadata_rx_csum - Get checksum status with additional info.
> + * @ctx: XDP context pointer.
> + * @csum_status: Destination for checksum status.
> + * @csum_info: Destination for complete checksum or partial checksum offset.
> + *
> + * Status (@csum_status) is a bitfield that informs, what checksum
> + * processing was performed. Additional results of such processing,
> + * such as complete checksum or partial checksum offsets,
> + * are passed as info (@csum_info).
> + *
> + * Return:
> + * * Returns 0 on success or ``-errno`` on error.
> + * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc
> + * * ``-ENODATA``    : Checksum status is unknown
> + */
> +__bpf_kfunc int bpf_xdp_metadata_rx_csum(const struct xdp_md *ctx,
> +					 enum xdp_csum_status *csum_status,
> +					 union xdp_csum_info *csum_info)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  __diag_pop();
>  
>  BTF_SET8_START(xdp_metadata_kfunc_ids)
> -- 
> 2.41.0
>