On Sat, 27 Feb 2021 09:16:38 -0800 John Fastabend wrote:
> Willem de Bruijn wrote:
> > On Fri, Feb 26, 2021 at 4:23 PM Daniel Borkmann <dan...@iogearbox.net>
> > wrote:
> > >
> > > We noticed a GRO issue for UDP-based encaps such as vxlan/geneve when the
> > > csum for the UDP header itself is 0. In that case, GRO aggregation does
> > > not take place on the phys dev, but instead is deferred to the
> > > vxlan/geneve
> > > driver (see trace below).
> > >
> > > The reason is essentially that GRO aggregation bails out in
> > > udp_gro_receive()
> > > for such case when drivers marked the skb with CHECKSUM_UNNECESSARY (ice,
> > > i40e,
> > > others) where for non-zero csums 2abb7cdc0dc8 ("udp: Add support for doing
> > > checksum unnecessary conversion") promotes those skbs to CHECKSUM_COMPLETE
> > > and napi context has csum_valid set. This is however not the case for zero
> > > UDP csum (here: csum_cnt is still 0 and csum_valid continues to be false).
> > >
> > > At the same time 57c67ff4bd92 ("udp: additional GRO support") added
> > > matches
> > > on !uh->check ^ !uh2->check as part to determine candidates for
> > > aggregation,
> > > so it certainly is expected to handle zero csums in udp_gro_receive(). The
> > > purpose of the check added via 662880f44203 ("net: Allow GRO to use and
> > > set
> > > levels of checksum unnecessary") seems to catch bad csum and stop
> > > aggregation
> > > right away.
> > >
> > > One way to fix aggregation in the zero case is to only perform the
> > > !csum_valid
> > > check in udp_gro_receive() if uh->check is infact non-zero.
> >
> > Acked-by: Willem de Bruijn <will...@google.com>
>
> Acked-by: John Fastabend <john.fastab...@gmail.com>
Applied, thanks!
