Subject: Re: [net-next v4 07/16] i40e: Rx checksum offload for VXLAN

From: Joseph Gasparakis <[email-masked]>
Date: Thu, 2 Jan 2014 12:57:56 -0800 (PST)

On Thu, 2 Jan 2014, Or Gerlitz wrote:

> On Sat, Dec 28, 2013 at 5:22 AM, Jeff Kirsher
> <[email-masked]> wrote:
> > From: Joseph Gasparakis <[email-masked]>
> >
> > This implements receive offload for VXLAN for i40e.  The hardware
> > supports checksum offload/verification of the inner/outer header.
> >
> > Change-Id: I450db300af6713f2044fef1191a0d1d294c13369
> > Signed-off-by: Joseph Gasparakis <[email-masked]>
> > Signed-off-by: Jesse Brandeburg <[email-masked]>
> > Signed-off-by: Jeff Kirsher <[email-masked]>
> > ---
> >  drivers/net/ethernet/intel/i40e/i40e.h      |  1 +
> >  drivers/net/ethernet/intel/i40e/i40e_txrx.c | 57 ++++++++++++++++++++++++++---
> >  drivers/net/ethernet/intel/i40e/i40e_type.h | 51 ++++++++++++++------------
> >  3 files changed, 81 insertions(+), 28 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e.h b/drivers/net/ethernet/intel/i40e/i40e.h
> > index 6f1edc1..34a54e7 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e.h
> > +++ b/drivers/net/ethernet/intel/i40e/i40e.h
> > @@ -29,6 +29,7 @@
> >  #define _I40E_H_
> >
> >  #include <net/tcp.h>
> > +#include <net/udp.h>
> >  #include <linux/init.h>
> >  #include <linux/types.h>
> >  #include <linux/errno.h>
> > diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > index 01d0334..a978451 100644
> > --- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > +++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
> > @@ -860,12 +860,25 @@ static void i40e_receive_skb(struct i40e_ring *rx_ring,
> >   * @skb: skb currently being received and modified
> >   * @rx_status: status value of last descriptor in packet
> >   * @rx_error: error value of last descriptor in packet
> > + * @rx_ptype: ptype value of last descriptor in packet
> >   **/
> >  static inline void i40e_rx_checksum(struct i40e_vsi *vsi,
> >                                     struct sk_buff *skb,
> >                                     u32 rx_status,
> > -                                   u32 rx_error)
> > +                                   u32 rx_error,
> > +                                   u16 rx_ptype)
> >  {
> > +       bool ipv4_tunnel, ipv6_tunnel;
> > +       __wsum rx_udp_csum;
> > +       __sum16 csum;
> > +       struct iphdr *iph;
> > +
> > +       ipv4_tunnel = (rx_ptype > I40E_RX_PTYPE_GRENAT4_MAC_PAY3) &&
> > +                     (rx_ptype < I40E_RX_PTYPE_GRENAT4_MACVLAN_IPV6_ICMP_PAY4);
> > +       ipv6_tunnel = (rx_ptype > I40E_RX_PTYPE_GRENAT6_MAC_PAY3) &&
> > +                     (rx_ptype < I40E_RX_PTYPE_GRENAT6_MACVLAN_IPV6_ICMP_PAY4);
> > +
> > +       skb->encapsulation = ipv4_tunnel || ipv6_tunnel;

skb->encapulation is set (or not) here.

> >         skb->ip_summed = CHECKSUM_NONE;
> >
> >         /* Rx csum enabled and ip headers found? */
> > @@ -873,13 +886,43 @@ static inline void i40e_rx_checksum(struct i40e_vsi *vsi,
> >               rx_status & (1 << I40E_RX_DESC_STATUS_L3L4P_SHIFT)))
> >                 return;
> >
> > -       /* IP or L4 checksum error */
> > +       /* IP or L4 or outmost IP checksum error */
> >         if (rx_error & ((1 << I40E_RX_DESC_ERROR_IPE_SHIFT) |
> > -                       (1 << I40E_RX_DESC_ERROR_L4E_SHIFT))) {
> > +                       (1 << I40E_RX_DESC_ERROR_L4E_SHIFT) |
> > +                       (1 << I40E_RX_DESC_ERROR_EIPE_SHIFT))) {
> >                 vsi->back->hw_csum_rx_error++;
> >                 return;
> >         }
> >
> > +       if (ipv4_tunnel &&
> > +           !(rx_status & (1 << I40E_RX_DESC_STATUS_UDP_0_SHIFT))) {
> > +               /* If VXLAN traffic has an outer UDPv4 checksum we need to check
> > +                * it in the driver, hardware does not do it for us.
> > +                * Since L3L4P bit was set we assume a valid IHL value (>=5)
> > +                * so the total length of IPv4 header is IHL*4 bytes
> > +                */
> 
> The comment says that the driver has to compute the udp checksum
> **if** the packet has an outer udp checksum,
> but the driver call to issue checksumming is done unconditionally
> 

This code runs when the right bits are set in the rx hardware descriptor 
field (rx_ptype and rx_status), which implies the hardware has detected 
ipv4 tunneling and there is non zero UDP csum.

> > +               skb->transport_header = skb->mac_header +
> > +                                       sizeof(struct ethhdr) +
> > +                                       (ip_hdr(skb)->ihl * 4);
> > +
> > +               /* Add 4 bytes for VLAN tagged packets */
> > +               skb->transport_header += (skb->protocol == htons(ETH_P_8021Q) ||
> > +                                         skb->protocol == htons(ETH_P_8021AD))
> > +                                         ? VLAN_HLEN : 0;
> > +
> > +               rx_udp_csum = udp_csum(skb);
> > +               iph = ip_hdr(skb);
> > +               csum = csum_tcpudp_magic(
> > +                               iph->saddr, iph->daddr,
> > +                               (skb->len - skb_transport_offset(skb)),
> > +                               IPPROTO_UDP, rx_udp_csum);
> > +
> > +               if (udp_hdr(skb)->check != csum) {
> > +                       vsi->back->hw_csum_rx_error++;
> > +                       return;
> > +               }
> > +       }
> > +
> >         skb->ip_summed = CHECKSUM_UNNECESSARY;
> >  }
> 
> Commit 0afb1666fe4 "vxlan: Add capability of Rx checksum offload for
> inner packet" dictates that
> the driver is expected to set the skb->encapsulation bit, this is
> missing here, and indeed in vxlan_udp_encap_recv
> your setting of ip_summed will be ignored and over-rided with
> CHECKSUM_NONE, agree?

It is setting skb->encapsulation when hw detects it. I have pointed it out 
above.

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