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

[Larysa Zaremba <larysa.zaremba@intel.com>]

On Mon, Jul 03, 2023 at 01:38:27PM -0700, John Fastabend wrote:
> 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 <larysa.zaremba@intel.com>
> > ---
> >  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.
>

I see no value in returning CHECKSUM_COMPLETE without the actual checksum value. 
Same with CHECKSUM_PARTIAL and csum_start. Returning those values too would 
overcomplicate the function signature.
 
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> > +
> >  __diag_pop();
> >  
> >  BTF_SET8_START(xdp_metadata_kfunc_ids)
> > -- 
> > 2.41.0
> >