On Thu, Jan 28, 2021 at 4:29 AM Xin Long <lucien....@gmail.com> wrote:
>
> NETIF_F_IP|IPV6_CSUM feature flag indicates UDP and TCP csum offload
> while NETIF_F_HW_CSUM feature flag indicates ip generic csum offload
> for HW, which includes not only for TCP/UDP csum, but also for other
> protocols' csum like GRE's.
>
> However, in skb_csum_hwoffload_help() it only checks features against
> NETIF_F_CSUM_MASK(NETIF_F_HW|IP|IPV6_CSUM). So if it's a non TCP/UDP
> packet and the features doesn't support NETIF_F_HW_CSUM, but supports
> NETIF_F_IP|IPV6_CSUM only, it would still return 0 and leave the HW
> to do csum.
>
> This patch is to support ip generic csum processing by checking
> NETIF_F_HW_CSUM for all protocols, and check (NETIF_F_IP_CSUM |
> NETIF_F_IPV6_CSUM) only for TCP and UDP.
>
> Note that we're using skb->csum_offset to check if it's a TCP/UDP
> proctol, this might be fragile. However, as Alex said, for now we
> only have a few L4 protocols that are requesting Tx csum offload,
> we'd better fix this until a new protocol comes with a same csum
> offset.
>
> v1->v2:
> - not extend skb->csum_not_inet, but use skb->csum_offset to tell
> if it's an UDP/TCP csum packet.
> v2->v3:
> - add a note in the changelog, as Willem suggested.
>
> Suggested-by: Alexander Duyck <alexander.du...@gmail.com>
> Signed-off-by: Xin Long <lucien....@gmail.com>
> ---
> net/core/dev.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 6df3f1b..aae116d 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -3621,7 +3621,18 @@ int skb_csum_hwoffload_help(struct sk_buff *skb,
> return !!(features & NETIF_F_SCTP_CRC) ? 0 :
> skb_crc32c_csum_help(skb);
>
> - return !!(features & NETIF_F_CSUM_MASK) ? 0 : skb_checksum_help(skb);
> + if (features & NETIF_F_HW_CSUM)
> + return 0;
> +
> + if (features & (NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM)) {
Should this check the specific feature flag against skb->protocol? I
don't know if there are actually instances that only support one of
the two flags.
> + switch (skb->csum_offset) {
> + case offsetof(struct tcphdr, check):
> + case offsetof(struct udphdr, check):
> + return 0;
> + }
> + }
> +
> + return skb_checksum_help(skb);
> }
> EXPORT_SYMBOL(skb_csum_hwoffload_help);
>
> --
> 2.1.0
>
