XDP hardware hints discussion mail archive
 help / color / mirror / Atom feed
From: Larysa Zaremba <larysa.zaremba@intel.com>
To: Willem de Bruijn <willemdebruijn.kernel@gmail.com>,
	Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Alexei Starovoitov <alexei.starovoitov@gmail.com>,
	bpf <bpf@vger.kernel.org>, Alexei Starovoitov <ast@kernel.org>,
	Daniel Borkmann <daniel@iogearbox.net>,
	Andrii Nakryiko <andrii@kernel.org>,
	Martin KaFai Lau <martin.lau@linux.dev>,
	Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
	John Fastabend <john.fastabend@gmail.com>,
	KP Singh <kpsingh@kernel.org>,
	Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
	Jiri Olsa <jolsa@kernel.org>, David Ahern <dsahern@gmail.com>,
	Jakub Kicinski <kuba@kernel.org>,
	Willem de Bruijn <willemb@google.com>,
	Jesper Dangaard Brouer <brouer@redhat.com>,
	Anatoly Burakov <anatoly.burakov@intel.com>,
	Alexander Lobakin <alexandr.lobakin@intel.com>,
	Magnus Karlsson <magnus.karlsson@gmail.com>,
	Maryam Tahhan <mtahhan@redhat.com>,
	xdp-hints@xdp-project.net,
	Network Development <netdev@vger.kernel.org>,
	Simon Horman <simon.horman@corigine.com>
Subject: [xdp-hints] Re: [PATCH bpf-next v4 12/21] xdp: Add checksum hint
Date: Mon, 31 Jul 2023 12:52:02 +0200	[thread overview]
Message-ID: <ZMeSUrOfhq9dWz6f@lincoln> (raw)
In-Reply-To: <64c661de227c2_11bfb629493@willemb.c.googlers.com.notmuch>

On Sun, Jul 30, 2023 at 09:13:02AM -0400, Willem de Bruijn wrote:
> Alexei Starovoitov wrote:
> > On Sat, Jul 29, 2023 at 9:15 AM Willem de Bruijn
> > <willemdebruijn.kernel@gmail.com> wrote:
> > >
> > > Alexei Starovoitov wrote:
> > > > On Fri, Jul 28, 2023 at 07:39:14PM +0200, Larysa Zaremba wrote:
> > > > >
> > > > > +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_PARTIAL makes sense on TX, but this RX. I don't see in the above.
> > >
> > > It can be observed on RX when packets are looped.
> > >
> > > This may be observed even in XDP on veth.
> > 
> > veth and XDP is a broken combination. GSO packets coming out of containers
> > cannot be parsed properly by XDP.
> > It was added mainly for testing. Just like "generic XDP".
> > bpf progs at skb layer is much better fit for veth.
> 
> Ok. Still, seems forward looking and little cost to define the
> constant?
>

+1
CHECKSUM_PARTIAL is mostly for testing and removing/adding it doesn't change 
anything from the perspective of the user that does not use it, so I think it is 
worth having.

> > > > > +   /* Checksum, calculated over the whole packet.
> > > > > +    * Available, if ``status & XDP_CHECKSUM_COMPLETE``.
> > > > > +    */
> > > > > +   u32 checksum;
> > > >
> > > > imo XDP RX should only support XDP_CHECKSUM_COMPLETE with u32 checksum
> > > > or XDP_CHECKSUM_UNNECESSARY.
> > > >
> > > > > +};
> > > > > +
> > > > > +enum xdp_csum_status {
> > > > > +   /* HW had parsed several transport headers and validated their
> > > > > +    * checksums, same as ``CHECKSUM_UNNECESSARY`` in ``sk_buff``.
> > > > > +    * 3 least significant bytes contain number of consecutive checksums,
> > > > > +    * 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,
> > > >
> > > > I don't see what bpf prog suppose to do with these levels.
> > > > The driver should pick between 3:
> > > > XDP_CHECKSUM_UNNECESSARY, XDP_CHECKSUM_COMPLETE, XDP_CHECKSUM_NONE.
> > > >
> > > > No levels and no anything partial. please.
> > >
> > > This levels business is an unfortunate side effect of
> > > CHECKSUM_UNNECESSARY. For a packet with multiple checksum fields, what
> > > does the boolean actually mean? With these levels, at least that is
> > > well defined: the first N checksum fields.
> > 
> > If I understand this correctly this is intel specific feature that
> > other NICs don't have. skb layer also doesn't have such concept.

Please look into csum_level field in sk_buff. It is not the most used property 
in the kernel networking code, but it is certainly 1. used by networking stack 
2. set to non-zero value by many vendors.

So you do not need to search yourself, I'll copy-paste the docs for 
CHECKSUM_UNNECESSARY here:

 *   %CHECKSUM_UNNECESSARY is applicable to following protocols:
 *
 *     - TCP: IPv6 and IPv4.
 *     - UDP: IPv4 and IPv6. A device may apply CHECKSUM_UNNECESSARY to a
 *       zero UDP checksum for either IPv4 or IPv6, the networking stack
 *       may perform further validation in this case.
 *     - GRE: only if the checksum is present in the header.
 *     - SCTP: indicates the CRC in SCTP header has been validated.
 *     - FCOE: indicates the CRC in FC frame has been validated.
 *

Please, look at this:

 *   &sk_buff.csum_level indicates the number of consecutive checksums found in
 *   the packet minus one that have been verified as %CHECKSUM_UNNECESSARY.
 *   For instance if a device receives an IPv6->UDP->GRE->IPv4->TCP packet
 *   and a device is able to verify the checksums for UDP (possibly zero),
 *   GRE (checksum flag is set) and TCP, &sk_buff.csum_level would be set to
 *   two. If the device were only able to verify the UDP checksum and not
 *   GRE, either because it doesn't support GRE checksum or because GRE
 *   checksum is bad, skb->csum_level would be set to zero (TCP checksum is
 *   not considered in this case).

From: 
https://elixir.bootlin.com/linux/v6.5-rc4/source/include/linux/skbuff.h#L115

> > The driver should say CHECKSUM_UNNECESSARY when it's sure
> > or don't pretend that it checks the checksum and just say NONE.
> 

Well, in such case, most of the NICs that use CHECKSUM_UNNECESSARY would have to 
return CHECKSUM_NONE instead, because based on my quick search, they mostly 
return checksum level of 0 (no tunneling detected) or 1 (tunneling detected),
so they only parse headers up to a certain depth, meaning it's not possible
to tell whether there isn't another CHECKSUM_UNNECESSARY-eligible header hiding
in the payload, so those NIC cannot guarantee ALL the checksums present in the 
packet are correct. So, by your logic, we should make e.g. AF_XDP user re-check 
already verified checksums themselves, because HW "doesn't pretend that it 
checks the checksum and just says NONE".

> I did not know how much this was used, but quick grep for non constant
> csum_level shows devices from at least six vendors.

Yes, there are several vendors that set the csum_level, including broadcom 
(bnxt) and mellanox (mlx4 and mlx5).

Also, CHECKSUM_UNNECESSARY is found in 100+ drivers/net/ethernet files,
while csum_level is in like 20, which means overwhelming majority of 
CHECKSUM_UNNECESSARY NICs actually stay with the default checksum level of '0'
(they check only the outermost checksum - anything else needs to be verified by 
the networking stack).

  reply	other threads:[~2023-07-31 10:56 UTC|newest]

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-07-28 15:44 [xdp-hints] (no subject) Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 01/21] ice: make RX hash reading code more reusable Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 02/21] ice: make RX HW timestamp " Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 03/21] ice: make RX checksum checking " Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 04/21] ice: Make ptype internal to descriptor info processing Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 05/21] ice: Introduce ice_xdp_buff Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 06/21] ice: Support HW timestamp hint Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 07/21] ice: Support RX hash XDP hint Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 08/21] ice: Support XDP hints in AF_XDP ZC mode Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 09/21] xdp: Add VLAN tag hint Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 10/21] ice: Implement " Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 11/21] ice: use VLAN proto from ring packet context in skb path Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 12/21] xdp: Add checksum hint Larysa Zaremba
2023-07-28 21:53   ` [xdp-hints] " Alexei Starovoitov
2023-07-29 16:15     ` Willem de Bruijn
2023-07-29 18:04       ` Alexei Starovoitov
2023-07-30 13:13         ` Willem de Bruijn
2023-07-31 10:52           ` Larysa Zaremba [this message]
2023-08-01  1:03             ` Alexei Starovoitov
2023-08-02 13:27               ` Willem de Bruijn
2023-08-07 15:03                 ` Larysa Zaremba
2023-08-07 15:32               ` Larysa Zaremba
2023-08-07 17:06                 ` Stanislav Fomichev
2023-07-31 16:43           ` Jakub Kicinski
2023-08-07 15:08             ` Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 13/21] ice: Implement " Larysa Zaremba
2023-07-28 21:02   ` [xdp-hints] " kernel test robot
2023-07-28 21:02   ` kernel test robot
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 14/21] selftests/bpf: Allow VLAN packets in xdp_hw_metadata Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 15/21] net, xdp: allow metadata > 32 Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 16/21] selftests/bpf: Add flags and new hints to xdp_hw_metadata Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 17/21] veth: Implement VLAN tag and checksum XDP hint Larysa Zaremba
2023-07-29 22:13   ` [xdp-hints] " kernel test robot
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 18/21] net: make vlan_get_tag() return -ENODATA instead of -EINVAL Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 19/21] selftests/bpf: Use AF_INET for TX in xdp_metadata Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 20/21] selftests/bpf: Check VLAN tag and proto " Larysa Zaremba
2023-07-28 17:39 ` [xdp-hints] [PATCH bpf-next v4 21/21] selftests/bpf: check checksum state " Larysa Zaremba

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

  List information: https://lists.xdp-project.net/postorius/lists/xdp-hints.xdp-project.net/

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=ZMeSUrOfhq9dWz6f@lincoln \
    --to=larysa.zaremba@intel.com \
    --cc=alexandr.lobakin@intel.com \
    --cc=alexei.starovoitov@gmail.com \
    --cc=anatoly.burakov@intel.com \
    --cc=andrii@kernel.org \
    --cc=ast@kernel.org \
    --cc=bpf@vger.kernel.org \
    --cc=brouer@redhat.com \
    --cc=daniel@iogearbox.net \
    --cc=dsahern@gmail.com \
    --cc=haoluo@google.com \
    --cc=john.fastabend@gmail.com \
    --cc=jolsa@kernel.org \
    --cc=kpsingh@kernel.org \
    --cc=kuba@kernel.org \
    --cc=magnus.karlsson@gmail.com \
    --cc=martin.lau@linux.dev \
    --cc=mtahhan@redhat.com \
    --cc=netdev@vger.kernel.org \
    --cc=sdf@google.com \
    --cc=simon.horman@corigine.com \
    --cc=song@kernel.org \
    --cc=willemb@google.com \
    --cc=willemdebruijn.kernel@gmail.com \
    --cc=xdp-hints@xdp-project.net \
    --cc=yhs@fb.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox