Yuri Benditovich wrote:
The commit fc8b2a619469 ("net: more strict VIRTIO_NET_HDR_GSO_UDP_L4 validation") adds check of potential number of UDP segments vs UDP_MAX_SEGMENTS in linux/virtio_net.h. After this change certification test of USO guest-to-guest transmit on Windows driver for virtio-net device fails, for example with packet size of ~64K and mss of 536 bytes. In general the USO should not be more restrictive than TSO. Indeed, in case of unreasonably small mss a lot of segments can cause queue overflow and packet loss on the destination. Limit of 128 segments is good for any practical purpose, with minimal meaningful mss of 536 the maximal UDP packet will be divided to ~120 segments. The number of segments for UDP packets is validated vs UDP_MAX_SEGMENTS also in udp.c (v4,v6), this does not affect quest-to-guest path but does affect packets sent to host, for example. It is important to mention that UDP_MAX_SEGMENTS is kernel-only define and not available to user mode socket applications. In order to request MSS smaller than MTU the applications just uses setsockopt with SOL_UDP and UDP_SEGMENT and there is no limitations on socket API level.
Fixes: fc8b2a619469 ("net: more strict VIRTIO_NET_HDR_GSO_UDP_L4 validation") Signed-off-by: Yuri Benditovich yuri.benditovich@daynix.com
Reviewed-by: Willem de Bruijn willemb@google.com
No need for a cover letter for a single patch btw.