Subject: RE: [PATCH bpf-next v2 12/20] xdp: Add checksum level hint

From: John Fastabend <[email-masked]>
Date: Mon, 03 Jul 2023 13:38:27 -0700

Larysa Zaremba wrote:
> Implement functionality that enables drivers to expose to XDP code,
> whether checksums was checked and on what level.
> 
> Signed-off-by: Larysa Zaremba <[email-masked]>
> ---
>  Documentation/networking/xdp-rx-metadata.rst |  3 +++
>  include/linux/netdevice.h                    |  1 +
>  include/net/xdp.h                            |  2 ++
>  kernel/bpf/offload.c                         |  2 ++
>  net/core/xdp.c                               | 21 ++++++++++++++++++++
>  5 files changed, 29 insertions(+)
> 
> diff --git a/Documentation/networking/xdp-rx-metadata.rst b/Documentation/networking/xdp-rx-metadata.rst
> index ea6dd79a21d3..4ec6ddfd2a52 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_lvl
> +
>  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 4fa4380e6d89..569563687172 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -1660,6 +1660,7 @@ struct xdp_metadata_ops {
>  			       enum xdp_rss_hash_type *rss_type);
>  	int	(*xmo_rx_vlan_tag)(const struct xdp_md *ctx, u16 *vlan_tag,
>  				   __be16 *vlan_proto);
> +	int	(*xmo_rx_csum_lvl)(const struct xdp_md *ctx, u8 *csum_level);
>  };
>  
>  /**
> diff --git a/include/net/xdp.h b/include/net/xdp.h
> index 89c58f56ffc6..61ed38fa79d1 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_LVL, \
> +			   bpf_xdp_metadata_rx_csum_lvl) \
>  
>  enum {
>  #define XDP_METADATA_KFUNC(name, _) name,
> diff --git a/kernel/bpf/offload.c b/kernel/bpf/offload.c
> index 986e7becfd42..a133fb775f49 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_LVL))
> +		p = ops->xmo_rx_csum_lvl;
>  out:
>  	up_read(&bpf_devs_lock);
>  
> diff --git a/net/core/xdp.c b/net/core/xdp.c
> index f6262c90e45f..c666d3e0a26c 100644
> --- a/net/core/xdp.c
> +++ b/net/core/xdp.c
> @@ -758,6 +758,27 @@ __bpf_kfunc int bpf_xdp_metadata_rx_vlan_tag(const struct xdp_md *ctx, u16 *vlan
>  	return -EOPNOTSUPP;
>  }
>  
> +/**
> + * bpf_xdp_metadata_rx_csum_lvl - Get depth at which HW has checked the checksum.
> + * @ctx: XDP context pointer.
> + * @csum_level: Return value pointer.
> + *
> + * In case of success, csum_level contains depth of the last verified checksum.
> + * If only the outermost checksum was verified, csum_level is 0, if both
> + * encapsulation and inner transport checksums were verified, csum_level is 1,
> + * and so on.
> + * For more details, refer to csum_level field in sk_buff.
> + *
> + * Return:
> + * * Returns 0 on success or ``-errno`` on error.
> + * * ``-EOPNOTSUPP`` : device driver doesn't implement kfunc
> + * * ``-ENODATA``    : Checksum was not validated
> + */
> +__bpf_kfunc int bpf_xdp_metadata_rx_csum_lvl(const struct xdp_md *ctx, u8 *csum_level)

Istead of ENODATA should we return what would be put in the ip_summed field
CHECKSUM_{NONE, UNNECESSARY, COMPLETE, PARTIAL}? Then sig would be,

 bpf_xdp_metadata_rx_csum_lvl(const struct xdp_md *ctx, u8 *type, u8 *lvl);

or something like that? Or is the thought that its not really necessary?
I don't have a strong preference but figured it was worth asking.

> +{
> +	return -EOPNOTSUPP;
> +}
> +
>  __diag_pop();
>  
>  BTF_SET8_START(xdp_metadata_kfunc_ids)
> -- 
> 2.41.0
>