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authorJakub Sitnicki <jakub@cloudflare.com>2024-06-26 19:51:26 +0200
committerJakub Kicinski <kuba@kernel.org>2024-06-29 03:12:59 +0200
commit10154dbded6d6a2fecaebdfda206609de0f121a9 (patch)
tree1be1d4d1d38564301d631e093029ab334aed7458 /net/ipv4
parentMerge branch 'net-selftests-mirroring-cleanup' into main (diff)
downloadlinux-10154dbded6d6a2fecaebdfda206609de0f121a9.tar.xz
linux-10154dbded6d6a2fecaebdfda206609de0f121a9.zip
udp: Allow GSO transmit from devices with no checksum offload
Today sending a UDP GSO packet from a TUN device results in an EIO error: import fcntl, os, struct from socket import * TUNSETIFF = 0x400454CA IFF_TUN = 0x0001 IFF_NO_PI = 0x1000 UDP_SEGMENT = 103 tun_fd = os.open("/dev/net/tun", os.O_RDWR) ifr = struct.pack("16sH", b"tun0", IFF_TUN | IFF_NO_PI) fcntl.ioctl(tun_fd, TUNSETIFF, ifr) os.system("ip addr add 192.0.2.1/24 dev tun0") os.system("ip link set dev tun0 up") s = socket(AF_INET, SOCK_DGRAM) s.setsockopt(SOL_UDP, UDP_SEGMENT, 1200) s.sendto(b"x" * 3000, ("192.0.2.2", 9)) # EIO This is due to a check in the udp stack if the egress device offers checksum offload. While TUN/TAP devices, by default, don't advertise this capability because it requires support from the TUN/TAP reader. However, the GSO stack has a software fallback for checksum calculation, which we can use. This way we don't force UDP_SEGMENT users to handle the EIO error and implement a segmentation fallback. Lift the restriction so that UDP_SEGMENT can be used with any egress device. We also need to adjust the UDP GSO code to match the GSO stack expectation about ip_summed field, as set in commit 8d63bee643f1 ("net: avoid skb_warn_bad_offload false positives on UFO"). Otherwise we will hit the bad offload check. Users should, however, expect a potential performance impact when batch-sending packets with UDP_SEGMENT without checksum offload on the egress device. In such case the packet payload is read twice: first during the sendmsg syscall when copying data from user memory, and then in the GSO stack for checksum computation. This double memory read can be less efficient than a regular sendmsg where the checksum is calculated during the initial data copy from user memory. Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com> Reviewed-by: Willem de Bruijn <willemb@google.com> Link: https://patch.msgid.link/20240626-linux-udpgso-v2-1-422dfcbd6b48@cloudflare.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Diffstat (limited to 'net/ipv4')
-rw-r--r--net/ipv4/udp.c3
-rw-r--r--net/ipv4/udp_offload.c8
2 files changed, 9 insertions, 2 deletions
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index d08bf16d476d..ed97df6af14d 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -938,8 +938,7 @@ static int udp_send_skb(struct sk_buff *skb, struct flowi4 *fl4,
kfree_skb(skb);
return -EINVAL;
}
- if (skb->ip_summed != CHECKSUM_PARTIAL || is_udplite ||
- dst_xfrm(skb_dst(skb))) {
+ if (is_udplite || dst_xfrm(skb_dst(skb))) {
kfree_skb(skb);
return -EIO;
}
diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
index 59448a2dbf2c..aa2e0a28ca61 100644
--- a/net/ipv4/udp_offload.c
+++ b/net/ipv4/udp_offload.c
@@ -357,6 +357,14 @@ struct sk_buff *__udp_gso_segment(struct sk_buff *gso_skb,
else
uh->check = gso_make_checksum(seg, ~check) ? : CSUM_MANGLED_0;
+ /* On the TX path, CHECKSUM_NONE and CHECKSUM_UNNECESSARY have the same
+ * meaning. However, check for bad offloads in the GSO stack expects the
+ * latter, if the checksum was calculated in software. To vouch for the
+ * segment skbs we actually need to set it on the gso_skb.
+ */
+ if (gso_skb->ip_summed == CHECKSUM_NONE)
+ gso_skb->ip_summed = CHECKSUM_UNNECESSARY;
+
/* update refcount for the packet */
if (copy_dtor) {
int delta = sum_truesize - gso_skb->truesize;