[dpdk-stable] [PATCH v1] net/ixgbe: adjust error for UDP with zero checksum

[David Marchand]

Hello Haiyue,

Thanks for working on it quickly.
Cc: ARM maintainers.

On Tue, Feb 2, 2021 at 8:23 AM Haiyue Wang <haiyue.wang at intel.com> wrote:
>
> There is an 82599 errata that UDP frames with a zero checksum are
> incorrectly marked as checksum invalid by the hardware.  This was

Maybe add a reference to the 82599 hw errata, is this listed in the datasheet?


> leading to misleading PKT_RX_L4_CKSUM_BAD flag. This patch adds a
> test around this checksum error flag set for this condition.
>
> 1. UDP Test
>   sendp(Ether()/IP()/UDP(chksum=0)/Raw("a"*100), iface="ens802f0")
>   port 0/queue 0: received 1 packets
>     ol_flags: PKT_RX_L4_CKSUM_GOOD PKT_RX_IP_CKSUM_GOOD
>
> 2. TCP Test
>   sendp(Ether()/IP()/TCP(chksum=0)/Raw("a"*100), iface="ens802f0")
>   port 0/queue 0: received 1 packets
>     ol_flags: PKT_RX_L4_CKSUM_BAD PKT_RX_IP_CKSUM_GOOD
>
> Bugzilla ID: 629

The problem has always been present, so I would flag:
Fixes: af75078fece3 ("first public release")

> Cc: stable at dpdk.org
>

Reported-by: Paolo Valerio <pvalerio at redhat.com>
> Signed-off-by: Haiyue Wang <haiyue.wang at intel.com>
> ---
>  doc/guides/nics/ixgbe.rst              |  6 ++++
>  drivers/net/ixgbe/ixgbe_rxtx.c         | 27 +++++++++++---
>  drivers/net/ixgbe/ixgbe_rxtx.h         |  2 ++
>  drivers/net/ixgbe/ixgbe_rxtx_vec_sse.c | 49 ++++++++++++++++++++------
>  4 files changed, 70 insertions(+), 14 deletions(-)
>
> diff --git a/doc/guides/nics/ixgbe.rst b/doc/guides/nics/ixgbe.rst
> index 696cbd93b..de210b7b8 100644
> --- a/doc/guides/nics/ixgbe.rst
> +++ b/doc/guides/nics/ixgbe.rst
> @@ -287,6 +287,12 @@ the VFs which are required.::
>  Currently hot-plugging of representor ports is not supported so all required
>  representors must be specified on the creation of the PF.
>
> +Limitations or Known issues
> +---------------------------
> +The 82599 hardware errata: UDP frames with a zero checksum can be marked as
> +checksum errors. To support zero checksum, the UDP checksum is always marked
> +as good.
> +

If the driver/hw can't report a valid checksum hint, it should
announce it does not know if the checksum is valid (neither bad, nor
good).

So the workaround for udp packets (on this hw model) would be to
report PKT_RX_L4_CKSUM_UNKNOWN.
The sw application will then have to recompute the checksum itself if needed.


-- 
David Marchand