• Eric Dumazet's avatar
    net: fix possible wrong checksum generation · cef401de
    Eric Dumazet authored
    Pravin Shelar mentioned that GSO could potentially generate
    wrong TX checksum if skb has fragments that are overwritten
    by the user between the checksum computation and transmit.
    
    He suggested to linearize skbs but this extra copy can be
    avoided for normal tcp skbs cooked by tcp_sendmsg().
    
    This patch introduces a new SKB_GSO_SHARED_FRAG flag, set
    in skb_shinfo(skb)->gso_type if at least one frag can be
    modified by the user.
    
    Typical sources of such possible overwrites are {vm}splice(),
    sendfile(), and macvtap/tun/virtio_net drivers.
    
    Tested:
    
    $ netperf -H 7.7.8.84
    MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to
    7.7.8.84 () port 0 AF_INET
    Recv   Send    Send
    Socket Socket  Message  Elapsed
    Size   Size    Size     Time     Throughput
    bytes  bytes   bytes    secs.    10^6bits/sec
    
     87380  16384  16384    10.00    3959.52
    
    $ netperf -H 7.7.8.84 -t TCP_SENDFILE
    TCP SENDFILE TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 7.7.8.84 ()
    port 0 AF_INET
    Recv   Send    Send
    Socket Socket  Message  Elapsed
    Size   Size    Size     Time     Throughput
    bytes  bytes   bytes    secs.    10^6bits/sec
    
     87380  16384  16384    10.00    3216.80
    
    Performance of the SENDFILE is impacted by the extra allocation and
    copy, and because we use order-0 pages, while the TCP_STREAM uses
    bigger pages.
    Reported-by: default avatarPravin Shelar <pshelar@nicira.com>
    Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    cef401de
tun.c 53.3 KB