Re: [PATCH v5 net-next 02/13] net: allow gso_max_size to exceed 65536

On Mon, May 9, 2022 at 7:09 PM Eric Dumazet [off-list ref] wrote:

Alexander used :

+                       if (sk->sk_gso_max_size > GSO_LEGACY_MAX_SIZE &&
+                           (!IS_ENABLED(CONFIG_IPV6) || sk->sk_family
!= AF_INET6 ||
+                            !sk_is_tcp(sk) ||
ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr)))
+                               sk->sk_gso_max_size = GSO_LEGACY_MAX_SIZE;

I guess we could simply allow gso_max_size to be bigger than
GSO_LEGACY_MAX_SIZE only
if IS_ENABLED(CONFIG_IPV6)

So the above code could really be:

#if IS_ENABLED(CONFIG_IPV6)
                       if (sk->sk_gso_max_size > GSO_LEGACY_MAX_SIZE &&
                           (sk->sk_family != AF_INET6 ||
                            !sk_is_tcp(sk) ||
ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr)))
                               sk->sk_gso_max_size = GSO_LEGACY_MAX_SIZE;
#endif

In v6, I will squash the following diff to Alexander patch:

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index dfd57a647c97ed0f400ffe89c73919367a900f75..6bd9e09b34ec583a05a929ca979511e6423dbeb7

100644

--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h

@@ -2271,8 +2271,13 @@ struct net_device {

 /* TCP minimal MSS is 8 (TCP_MIN_GSO_SIZE),
  * and shinfo->gso_segs is a 16bit field.
+ * If IPV6 is not enabled, we keep legacy value.
  */
+#if IS_ENABLED(CONFIG_IPV6)
 #define GSO_MAX_SIZE           (8 * GSO_MAX_SEGS)
+#else
+#define GSO_MAX_SIZE           GSO_LEGACY_MAX_SIZE
+#endif

        unsigned int            gso_max_size;
 #define TSO_LEGACY_MAX_SIZE    65536

diff --git a/net/core/dev.c b/net/core/dev.c
index 7349f75891d5724a060781abc80a800bdf835f74..4be3695846520af18a687cdcaa70c5f327ba94e8

100644

--- a/net/core/dev.c
+++ b/net/core/dev.c

@@ -3003,7 +3003,7 @@ EXPORT_SYMBOL(netif_set_real_num_queues);
  */
 void netif_set_tso_max_size(struct net_device *dev, unsigned int size)
 {
-       dev->tso_max_size = size;
+       dev->tso_max_size = min(GSO_MAX_SIZE, size);
        if (size < READ_ONCE(dev->gso_max_size))
                netif_set_gso_max_size(dev, size);
 }

diff --git a/net/core/sock.c b/net/core/sock.c
index f7c3171078b6fccd25757e8fe54dd56a2a674238..2a931f396472108ccedcd3d08189c63775caecff

100644

--- a/net/core/sock.c
+++ b/net/core/sock.c

@@ -2312,10 +2312,13 @@ void sk_setup_caps(struct sock *sk, struct

dst_entry *dst)
                        sk->sk_route_caps |= NETIF_F_SG | NETIF_F_HW_CSUM;
                        /* pairs with the WRITE_ONCE() in
netif_set_gso_max_size() */
                        sk->sk_gso_max_size = READ_ONCE(dst->dev->gso_max_size);
+#if IS_ENABLED(CONFIG_IPV6)
                        if (sk->sk_gso_max_size > GSO_LEGACY_MAX_SIZE &&
-                           (!IS_ENABLED(CONFIG_IPV6) || sk->sk_family
!= AF_INET6 ||
-                            !sk_is_tcp(sk) ||
ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr)))
+                           (sk->sk_family != AF_INET6 ||
+                            !sk_is_tcp(sk) ||
+                            ipv6_addr_v4mapped(&sk->sk_v6_rcv_saddr)))
                                sk->sk_gso_max_size = GSO_LEGACY_MAX_SIZE;
+#endif
                        sk->sk_gso_max_size -= (MAX_TCP_HEADER + 1);
                        /* pairs with the WRITE_ONCE() in
netif_set_gso_max_segs() */
                        max_segs = max_t(u32,
READ_ONCE(dst->dev->gso_max_segs), 1);