Re: [dpdk-stable] [dpdk-dev] [PATCH] app/testpmd: fix l4 sw csum over multi segments

["Li, Xiaoyun" <xiaoyun.li@intel.com>]

Hi

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Friday, October 15, 2021 16:10
> To: Li, Xiaoyun <xiaoyun.li@intel.com>
> Cc: Yigit, Ferruh <ferruh.yigit@intel.com>; dev <dev@dpdk.org>; dpdk stable
> <stable@dpdk.org>
> Subject: Re: [dpdk-dev] [PATCH] app/testpmd: fix l4 sw csum over multi
> segments
> 
> Hello,
> 
> On Fri, Oct 15, 2021 at 7:27 AM Xiaoyun Li <xiaoyun.li@intel.com> wrote:
> >
> > In csum forwarding mode, software UDP/TCP csum calculation only takes
> > the first segment into account while using the whole packet length so
> > the calculation will read invalid memory region with multi-segments
> > packets and will get wrong value.
> > This patch fixes this issue.
> >
> > Fixes: af75078fece3 ("first public release")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Xiaoyun Li <xiaoyun.li@intel.com>
> > ---
> >  app/test-pmd/csumonly.c | 31 +++++++++++++++++++++++--------
> >  1 file changed, 23 insertions(+), 8 deletions(-)
> >
> > diff --git a/app/test-pmd/csumonly.c b/app/test-pmd/csumonly.c index
> > 090797318a..5df3be0a6f 100644
> > --- a/app/test-pmd/csumonly.c
> > +++ b/app/test-pmd/csumonly.c
> > @@ -18,7 +18,7 @@
> >  #include <rte_log.h>
> >  #include <rte_debug.h>
> >  #include <rte_cycles.h>
> > -#include <rte_memory.h>
> > +#include <rte_malloc.h>
> 
> This include caught my eye.
> 
> 
> >  #include <rte_memcpy.h>
> >  #include <rte_launch.h>
> >  #include <rte_eal.h>
> > @@ -56,6 +56,11 @@
> >  #define GRE_SUPPORTED_FIELDS   (GRE_CHECKSUM_PRESENT |
> GRE_KEY_PRESENT |\
> >                                  GRE_SEQUENCE_PRESENT)
> >
> > +/* When UDP or TCP or outer UDP csum offload is off, sw l4 csum is needed
> */
> > +#define UDP_TCP_CSUM            (DEV_TX_OFFLOAD_UDP_CKSUM |\
> > +                                DEV_TX_OFFLOAD_TCP_CKSUM |\
> > +                                DEV_TX_OFFLOAD_OUTER_UDP_CKSUM)
> > +
> >  /* We cannot use rte_cpu_to_be_16() on a constant in a switch/case */
> > #if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN  #define _htons(x)
> > ((uint16_t)((((x) & 0x00ffU) << 8) | (((x) & 0xff00U) >> 8))) @@
> > -602,12 +607,8 @@ process_outer_cksums(void *outer_l3_hdr, struct
> testpmd_offload_info *info,
> >         /* do not recalculate udp cksum if it was 0 */
> >         if (udp_hdr->dgram_cksum != 0) {
> >                 udp_hdr->dgram_cksum = 0;
> > -               if (info->outer_ethertype == _htons(RTE_ETHER_TYPE_IPV4))
> > -                       udp_hdr->dgram_cksum =
> > -                               rte_ipv4_udptcp_cksum(ipv4_hdr, udp_hdr);
> > -               else
> > -                       udp_hdr->dgram_cksum =
> > -                               rte_ipv6_udptcp_cksum(ipv6_hdr, udp_hdr);
> > +               udp_hdr->dgram_cksum = get_udptcp_checksum(outer_l3_hdr,
> > +                                       udp_hdr,
> > + info->outer_ethertype);
> >         }
> >
> >         return ol_flags;
> > @@ -802,6 +803,7 @@ pkt_burst_checksum_forward(struct fwd_stream *fs)
> >         struct rte_mbuf *m, *p;
> >         struct rte_ether_hdr *eth_hdr;
> >         void *l3_hdr = NULL, *outer_l3_hdr = NULL; /* can be IPv4 or
> > IPv6 */
> > +       uint8_t *l3_buf = NULL;
> >         void **gro_ctx;
> >         uint16_t gro_pkts_num;
> >         uint8_t gro_enable;
> > @@ -877,7 +879,19 @@ pkt_burst_checksum_forward(struct fwd_stream *fs)
> >                 rte_ether_addr_copy(&ports[fs->tx_port].eth_addr,
> >                                 &eth_hdr->src_addr);
> >                 parse_ethernet(eth_hdr, &info);
> > -               l3_hdr = (char *)eth_hdr + info.l2_len;
> > +               /* When sw csum is needed, multi-segs needs a buf to contain
> > +                * the whole packet for later UDP/TCP csum calculation.
> > +                */
> > +               if (m->nb_segs > 1 && !(tx_ol_flags & PKT_TX_TCP_SEG) &&
> > +                   !(tx_offloads & UDP_TCP_CSUM)) {
> > +                       l3_buf = rte_zmalloc("csum l3_buf",
> > +                                            info.pkt_len - info.l2_len,
> > +                                            RTE_CACHE_LINE_SIZE);
> 
> Rather than call a dyn allocation in datapath, can't we have a static buffer on
> the stack?

I wanted to do that. But the issue only happens when it's a large packet. Each hw has its own limitation on max packet size but it grows fast.
I'm not sure how large array should I use. 64K? Since total length in IP hdr is 16 bit.

BRs
Xiaoyun

> 
> 
> > +                       rte_pktmbuf_read(m, info.l2_len,
> > +                                        info.pkt_len - info.l2_len, l3_buf);
> > +                       l3_hdr = l3_buf;
> > +               } else
> > +                       l3_hdr = (char *)eth_hdr + info.l2_len;
> >
> >                 /* check if it's a supported tunnel */
> >                 if (txp->parse_tunnel) { @@ -1051,6 +1065,7 @@
> > pkt_burst_checksum_forward(struct fwd_stream *fs)
> >                         printf("tx: flags=%s", buf);
> >                         printf("\n");
> >                 }
> > +               rte_free(l3_buf);
> >         }
> >
> >         if (unlikely(gro_enable)) {
> > --
> > 2.25.1
> >
> 
> 
> --
> David Marchand