netdev - Re: [net-next PATCH 06/10] gre: Use GSO flags to determine csum need instead of GRE flags

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Date:	Sat, 6 Feb 2016 12:52:19 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Alexander Duyck <aduyck@...antis.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Alexander Duyck <alexander.duyck@...il.com>,
	Edward Cree <ecree@...arflare.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [net-next PATCH 06/10] gre: Use GSO flags to determine csum need
 instead of GRE flags

On Fri, Feb 5, 2016 at 3:28 PM, Alexander Duyck <aduyck@...antis.com> wrote:
> This patch updates the gre checksum path to follow something much closer to
> the UDP checksum path.  By doing this we can avoid needing to do as much
> header inspection and can just make use of the fields we were already
> reading in the sk_buff structure.
>
> Signed-off-by: Alexander Duyck <aduyck@...antis.com>
> ---
>  net/ipv4/gre_offload.c |   64 +++++++++++++++++++++++-------------------------
>  1 file changed, 30 insertions(+), 34 deletions(-)
>
> diff --git a/net/ipv4/gre_offload.c b/net/ipv4/gre_offload.c
> index 35a8dd35ed4e..c15441b5ff61 100644
> --- a/net/ipv4/gre_offload.c
> +++ b/net/ipv4/gre_offload.c
> @@ -18,14 +18,14 @@
>  static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
>                                        netdev_features_t features)
>  {
> +       int tnl_hlen = skb_inner_mac_header(skb) - skb_transport_header(skb);
>         struct sk_buff *segs = ERR_PTR(-EINVAL);
> -       int ghl;
>         struct gre_base_hdr *greh;
>         u16 mac_offset = skb->mac_header;
> -       int mac_len = skb->mac_len;
>         __be16 protocol = skb->protocol;
> -       int tnl_hlen;
> -       bool csum;
> +       u16 mac_len = skb->mac_len;
> +       int gre_offset, outer_hlen;
> +       bool need_csum;
>
>         if (unlikely(skb_shinfo(skb)->gso_type &
>                                 ~(SKB_GSO_TCPV4 |
> @@ -42,64 +42,60 @@ static struct sk_buff *gre_gso_segment(struct sk_buff *skb,
>         if (!skb->encapsulation)
>                 goto out;
>
> -       if (unlikely(!pskb_may_pull(skb, sizeof(*greh))))
> +       if (unlikely(tnl_hlen < sizeof(struct gre_base_hdr)))
>                 goto out;
>
> -       greh = (struct gre_base_hdr *)skb_transport_header(skb);
> -
> -       ghl = skb_inner_mac_header(skb) - skb_transport_header(skb);
> -       if (unlikely(ghl < sizeof(*greh)))
> +       if (unlikely(!pskb_may_pull(skb, tnl_hlen)))
>                 goto out;
>
> -       csum = !!(greh->flags & GRE_CSUM);
> -       if (csum)
> -               skb->encap_hdr_csum = 1;
> +       greh = (struct gre_base_hdr *)skb_transport_header(skb);
>
>         /* setup inner skb. */
>         skb->protocol = greh->protocol;
>         skb->encapsulation = 0;
> -
> -       if (unlikely(!pskb_may_pull(skb, ghl)))
> -               goto out;
> -
> -       __skb_pull(skb, ghl);
> +       __skb_pull(skb, tnl_hlen);
>         skb_reset_mac_header(skb);
>         skb_set_network_header(skb, skb_inner_network_offset(skb));
>         skb->mac_len = skb_inner_network_offset(skb);
>
> +       need_csum = !!(skb_shinfo(skb)->gso_type & SKB_GSO_GRE_CSUM);

Should we do a WARN_ON(need_csum && !(greh->flags & GRE_CSUM)) just to
be conservative?

> +       skb->encap_hdr_csum = need_csum;
> +
>         features &= skb->dev->hw_enc_features;
>
>         /* segment inner packet. */
>         segs = skb_mac_gso_segment(skb, features);
>         if (IS_ERR_OR_NULL(segs)) {
> -               skb_gso_error_unwind(skb, protocol, ghl, mac_offset, mac_len);
> +               skb_gso_error_unwind(skb, protocol, tnl_hlen, mac_offset,
> +                                    mac_len);
>                 goto out;
>         }
>
> +       outer_hlen = skb_tnl_header_len(skb);
> +       gre_offset = outer_hlen - tnl_hlen;
>         skb = segs;
> -       tnl_hlen = skb_tnl_header_len(skb);
>         do {
> -               __skb_push(skb, ghl);
> -               if (csum) {
> -                       __be32 *pcsum;
> -
> -                       skb_reset_transport_header(skb);
> -
> -                       greh = (struct gre_base_hdr *)
> -                           skb_transport_header(skb);
> -                       pcsum = (__be32 *)(greh + 1);
> -                       *pcsum = 0;
> -                       *(__sum16 *)pcsum = gso_make_checksum(skb, 0);
> -               }
> -               __skb_push(skb, tnl_hlen - ghl);
> +               __be32 *pcsum;
>
>                 skb_reset_inner_headers(skb);
>                 skb->encapsulation = 1;
>
> -               skb_reset_mac_header(skb);
> -               skb_set_network_header(skb, mac_len);
>                 skb->mac_len = mac_len;
>                 skb->protocol = protocol;
> +
> +               __skb_push(skb, outer_hlen);
> +               skb_reset_mac_header(skb);
> +               skb_set_network_header(skb, mac_len);
> +               skb_set_transport_header(skb, gre_offset);
> +
> +               if (!need_csum)
> +                       continue;
> +
> +               greh = (struct gre_base_hdr *)skb_transport_header(skb);
> +               pcsum = (__be32 *)(greh + 1);
> +
> +               *pcsum = 0;
> +               *(__sum16 *)pcsum = gso_make_checksum(skb, 0);
>         } while ((skb = skb->next));
>  out:
>         return segs;
>