Re: [dpdk-dev] [dpdk-stable] [PATCH 1/4] net/tap: fix Rx cksum flags on IP options packets

[Olivier Matz <olivier.matz@6wind.com>]

On Tue, Jun 08, 2021 at 03:34:36PM +0300, Andrew Rybchenko wrote:
> On 6/8/21 3:29 PM, Olivier Matz wrote:
> > Hi Ferruh, Andrew,
> > 
> > On Tue, Jun 08, 2021 at 01:13:59PM +0300, Andrew Rybchenko wrote:
> >> On 4/30/21 5:48 PM, Ferruh Yigit wrote:
> >>> On 4/27/2021 2:57 PM, Olivier Matz wrote:
> >>>> When packet type is IPV4_EXT, the checksum is always marked as good in
> >>>> the mbuf offload flags.
> >>>>
> >>>> Since we know the header lengths, we can easily call
> >>>> rte_ipv4_udptcp_cksum() in this case too.
> >>>>
> >>>> Fixes: 8ae3023387e9 ("net/tap: add Rx/Tx checksum offload support")
> >>>> Cc: stable@dpdk.org
> >>>>
> >>>> Signed-off-by: Olivier Matz <olivier.matz@6wind.com>
> >>>> ---
> >>>>  drivers/net/tap/rte_eth_tap.c | 4 ++--
> >>>>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>>>
> >>>> diff --git a/drivers/net/tap/rte_eth_tap.c b/drivers/net/tap/rte_eth_tap.c
> >>>> index 68baa18523..e7b185a4b5 100644
> >>>> --- a/drivers/net/tap/rte_eth_tap.c
> >>>> +++ b/drivers/net/tap/rte_eth_tap.c
> >>>> @@ -350,7 +350,7 @@ tap_verify_csum(struct rte_mbuf *mbuf)
> >>>>  		/* Don't verify checksum for multi-segment packets. */
> >>>>  		if (mbuf->nb_segs > 1)
> >>>>  			return;
> >>>> -		if (l3 == RTE_PTYPE_L3_IPV4) {
> >>>> +		if (l3 == RTE_PTYPE_L3_IPV4 || l3 == RTE_PTYPE_L3_IPV4_EXT) {
> >>>
> >>> Should we take 'RTE_PTYPE_L3_IPV4_EXT_UNKNOWN' into account?
> >>
> >> I think we should.
> > 
> > I think 'RTE_PTYPE_L3_IPV4_EXT_UNKNOWN' cannot happen here:
> > 
> > - mbuf->packet_type is generated by 
> 
> (), which cannot
> >   return 'RTE_PTYPE_L3_IPV4_EXT_UNKNOWN'
> 
> My question if it is guaranteed and the only possible branch.
> Can application set packet_type itself and do not call
> rte_net_get_ptype(). Yes, typically application knows
> if it has IPv4 options in the header or not, but theoretically
> could be unaware as well.

This function is called on the Rx path from pmd_rx_burst(), so
the application does not have access to the mbuf.

The software parser that sets the packet type returns either
RTE_PTYPE_L3_IPV4 if there is no option, or RTE_PTYPE_L3_IPV4_EXT
else. The value RTE_PTYPE_L3_IPV4_EXT_UNKNOWN is used by PMDs that don't
know if there are options.

> > - right above this code, we already returned if l3 is not in
> >   (RTE_PTYPE_L3_IPV4, RTE_PTYPE_L3_IPV4_EXT, RTE_PTYPE_L3_IPV6)
> 
> If so, it sounds like it should be allowed above as well.
> 
> > 
> >>>
> >>>>  			if (l4 == RTE_PTYPE_L4_UDP) {
> >>>>  				udp_hdr = (struct rte_udp_hdr *)l4_hdr;
> >>>>  				if (udp_hdr->dgram_cksum == 0) {
> >>>> @@ -364,7 +364,7 @@ tap_verify_csum(struct rte_mbuf *mbuf)
> >>>>  				}
> >>>>  			}
> >>>>  			cksum = ~rte_ipv4_udptcp_cksum(l3_hdr, l4_hdr);
> >>>> -		} else if (l3 == RTE_PTYPE_L3_IPV6) {
> >>>> +		} else { /* l3 == RTE_PTYPE_L3_IPV6, checked above */
> >>>>  			cksum = ~rte_ipv6_udptcp_cksum(l3_hdr, l4_hdr);
> >>>>  		}
> >>>>  		mbuf->ol_flags |= cksum ?
> >>>>
> >>
>