Shmulik Ladkani <shmulik.ladk...@gmail.com> wrote: > > Normal ipv4 routing via vm1, no iptables etc. present, so > > > > we have hypervisor 1500 -> 1500 VM1 1280 -> 1280 VM2 > > > > Turning off gro avoids this problem. > > I hit the BUG only when VM2's mtu is not set to 1280 (kept to the 1500 > default).
Right, > Otherwise, Hypervisor's TCP stack (sender) uses TCP MSS advertised by > VM2 (which is 1240 if VM2 mtu properly configured), thus GRO taking > place in VM1's eth0 is based on arriving segments (sized 1240). True. > Only if VM2 has mtu of 1500, the MSS seen by Hypervisor during handshake > is 1460, thus GRO acting on VM1's eth0 is based on 1460 byte segments. > This leads to "gso clamping" taking place, with the BUG in skb_segment > (which btw, seems sensitive to change in gso_size only if GRO was > merging into frag_list). > > Can you please acknowledge our setup and reproduction are aligned? Yes, seems setups are identical.
