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Date: Tue, 4 Jul 2023 13:19:24 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Jesper Dangaard Brouer <jbrouer@...hat.com>
CC: John Fastabend <john.fastabend@...il.com>, <brouer@...hat.com>,
<bpf@...r.kernel.org>, <ast@...nel.org>, <daniel@...earbox.net>,
<andrii@...nel.org>, <martin.lau@...ux.dev>, <song@...nel.org>, <yhs@...com>,
<kpsingh@...nel.org>, <sdf@...gle.com>, <haoluo@...gle.com>,
<jolsa@...nel.org>, David Ahern <dsahern@...il.com>, Jakub Kicinski
<kuba@...nel.org>, Willem de Bruijn <willemb@...gle.com>, Anatoly Burakov
<anatoly.burakov@...el.com>, Alexander Lobakin <alexandr.lobakin@...el.com>,
Magnus Karlsson <magnus.karlsson@...il.com>, Maryam Tahhan
<mtahhan@...hat.com>, <xdp-hints@...-project.net>, <netdev@...r.kernel.org>,
"David S. Miller" <davem@...emloft.net>, Alexander Duyck
<alexander.duyck@...il.com>
Subject: Re: [PATCH bpf-next v2 12/20] xdp: Add checksum level hint
On Tue, Jul 04, 2023 at 12:39:06PM +0200, Jesper Dangaard Brouer wrote:
> Cc. DaveM+Alex Duyck, as I value your insights on checksums.
>
> On 04/07/2023 11.24, Larysa Zaremba wrote:
> > 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@...el.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,
>
> I was thinking the same, what about checksum "type".
>
> > >
> > > 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.
>
> So, this kfunc bpf_xdp_metadata_rx_csum_lvl() success is it equivilent to
> CHECKSUM_UNNECESSARY?
This is 100% true for physical NICs, it's more complicated for veth, bacause it
often receives CHECKSUM_PARTIAL, which shouldn't normally apprear on RX, but is
treated by the network stack as a validated checksum, because there is no way
internally generated packet could be messed up. I would be grateful if you could
look at the veth patch and share your opinion about this.
>
> Looking at documentation[1] (generated from skbuff.h):
> [1] https://kernel.org/doc/html/latest/networking/skbuff.html#checksumming-of-received-packets-by-device
>
> Is the idea that we can add another kfunc (new signature) than can deal
> with the other types of checksums (in a later kernel release)?
>
Yes, that is the idea.
>
> > > > +{
> > > > + return -EOPNOTSUPP;
> > > > +}
> > > > +
> > > > __diag_pop();
> >
>
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