diff options
author | Jakub Sitnicki <jakub@cloudflare.com> | 2024-06-26 19:51:26 +0200 |
---|---|---|
committer | Jakub Kicinski <kuba@kernel.org> | 2024-06-29 03:12:59 +0200 |
commit | 10154dbded6d6a2fecaebdfda206609de0f121a9 (patch) | |
tree | 1be1d4d1d38564301d631e093029ab334aed7458 /net/ipv4 | |
parent | Merge branch 'net-selftests-mirroring-cleanup' into main (diff) | |
download | linux-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.c | 3 | ||||
-rw-r--r-- | net/ipv4/udp_offload.c | 8 |
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; |