Re: [PATCH net-next 2/3] net: add CSUM_T_IP_GENERIC csum_type

On Fri, Jan 22, 2021 at 2:13 AM Alexander Duyck
[off-list ref] wrote:

On Thu, Jan 21, 2021 at 12:46 AM Xin Long [off-list ref] wrote:

quoted

This patch is to extend csum_type field to 2 bits, and introduce
CSUM_T_IP_GENERIC csum type, and add the support for this in
skb_csum_hwoffload_help(), just like CSUM_T_SCTP_CRC.

Note here it moves dst_pending_confirm field below ndisc_nodetype
to avoid a memory hole.

Signed-off-by: Xin Long <lucien.xin@gmail.com>
---
 include/linux/skbuff.h |  5 +++--
 net/core/dev.c         | 17 +++++++++++++----
 2 files changed, 16 insertions(+), 6 deletions(-)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 67b0a01..d5011fb 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h

@@ -224,6 +224,7 @@

 #define CSUM_T_INET            0
 #define CSUM_T_SCTP_CRC                1
+#define CSUM_T_IP_GENERIC      2

 /* Maximum value in skb->csum_level */
 #define SKB_MAX_CSUM_LEVEL     3

@@ -839,11 +840,11 @@ struct sk_buff {
        __u8                    vlan_present:1;
        __u8                    csum_complete_sw:1;
        __u8                    csum_level:2;
-       __u8                    csum_type:1;
-       __u8                    dst_pending_confirm:1;
+       __u8                    csum_type:2;
 #ifdef CONFIG_IPV6_NDISC_NODETYPE
        __u8                    ndisc_nodetype:2;
 #endif
+       __u8                    dst_pending_confirm:1;

        __u8                    ipvs_property:1;
        __u8                    inner_protocol_type:1;

diff --git a/net/core/dev.c b/net/core/dev.c
index 3241de2..6d48af2 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -3617,11 +3617,20 @@ static struct sk_buff *validate_xmit_vlan(struct sk_buff *skb,
 int skb_csum_hwoffload_help(struct sk_buff *skb,
                            const netdev_features_t features)
 {
-       if (unlikely(skb_csum_is_sctp(skb)))
-               return !!(features & NETIF_F_SCTP_CRC) ? 0 :
-                       skb_crc32c_csum_help(skb);
+       if (likely(!skb->csum_type))
+               return !!(features & NETIF_F_CSUM_MASK) ? 0 :
+                      skb_checksum_help(skb);

-       return !!(features & NETIF_F_CSUM_MASK) ? 0 : skb_checksum_help(skb);
+       if (skb_csum_is_sctp(skb)) {
+               return !!(features & NETIF_F_SCTP_CRC) ? 0 :
+                      skb_crc32c_csum_help(skb);
+       } else if (skb->csum_type == CSUM_T_IP_GENERIC) {
+               return !!(features & NETIF_F_HW_CSUM) ? 0 :
+                      skb_checksum_help(skb);
+       } else {
+               pr_warn("Wrong csum type: %d\n", skb->csum_type);
+               return 1;
+       }

Is the only difference between CSUM_T_IP_GENERIC the fact that we
check for NETIF_F_HW_CSUM versus using NETIF_F_CSUM_MASK? If so I
don't think adding the new bit is adding all that much value. Instead
you could probably just catch this in the testing logic here.

You could very easily just fold CSUM_T_IP_GENERIC into CSUM_T_INET,
and then in the checks here you split up the checks for
NETIF_F_HW_CSUM as follows:

If so, better not to touch csum_not_inet now. I will drop the patch 1/3.

 if (skb_csum_is_sctp(skb))
    return !!(features & NETIF_F_SCTP_CRC) ? 0 : skb_crc32c_csum_help(skb);

if (skb->csum_type) {
    pr_warn("Wrong csum type: %d\n", skb->csum_type);
    return 1;
}

if (features & NETIF_F_HW_CSUM)
    return 0;

if (features & NETIF_F_CSUM_MASK) {
    switch (skb->csum_offset) {
    case offsetof(struct tcphdr, check):
    case offsetof(struct udphdr, check):
            return 0;
    }

Question is: is it reliable to check the type by skb->csum_offset?
What if one day there's another protocol, whose the checksum field
is on the same offset, which is also using the CSUM_T_IP_GENERIC?

}

return skb_checksum_help(skb);