Re: [dpdk-dev] Wrong TCP checksum of packets sent by Linux guest (virtIO/vhost)

["Gray, Mark D" <mark.d.gray@intel.com>]

> 
> Hi,
> 
> On 09/03/14 13:13, Xie, Huawei wrote:
> > Looping in the dpdk-ovs list.
> >
> > * Does the new vhost API allow a user to know if all the relevant
> > offloads have been turned on/off for that interface? It seems that
> > this is possible through the virtio_net structure but it would be good
> > to get some feedback from the relevant person working on DPDK
> > (Huawei?).
> >
> > * If this is the case, then it is probably in the realm of the vswitch
> > do the actual checksum (for VM-VM) or correctly configure the NIC when
> > sending out through the physical interface.
> >
> > Comments?
> >
> > Mark:
> > So far not supported. This is important as well in VxLan case. For the
> > packet flow Guest A->  virtio -> ..->OVDK->.. -> Guest B.
> > 1) If guest A and B are on different host machines, say A and B
> > respectively,  and if the nic on A supports vxlan checksum offload,
> > then both guest and host needn't generate checksum, the nic will generate
> checksum for both inner and outer packet.
> > 2) In VM2VM case, as it is trusted communication channel, could we
> > negotiate with the guest tcp stack not to verify checksum for received
> packet?
> The problem is that any TCP packet send by a vanilla Linux guest through
> vhost is incorrect (VM to anything, including other colocalied VMs). In other
> words, the VM cannot use TCP. QEMU options and ethtool -K csum off tso
> off ("TCP stack negociation") have no effect, maybe because the vhost
> backend is misbehaving.

This sounds like a DPDK issue. However, we did "clone and own" the vhost
code as it is a sample app. It may have changed since we integrated it.

We plan to use the vhost library interface when it is available on dpdk.org. So
that would pick up the latest version of the vhost code.

> 
> Franck