> > > > > > > Host is not aware of the IP stack of the VM. > > > How do you resolve mac address for the destination IP used in guest VM in > > host, and how do you program right source mac and destination mac of the > > QP in host using ibverbs client? > > > I was asking Aviad in Mellanox to use devx interface do have passthrough > > programming. > > > So want to understand how are you doing this QEMU as its close to > > production now? > > > > Not sure i fully understand your question, ex why host needs to know the > > guest IP. > > Anyway, the flow is like this: > > - In guest, ib_core calls the driver's add_gid hook when gid entry is > > created > > - Driver in guest passes binding info to qemu device (sgid and gid) > > - qemu device adds this gid to host gid table (via netlink or QMP), note > > that sgid in host probably is different. Please also note that at this > > stage we have this gid defined twice in the fabric but since one is in > > guest, which is hidden, we are ok. (1098) > > - When guest creates QP it passes the guest sgid to qemu device which > > replace it with the host sgid. (#436) > > > > Since gid is defined in the host the all the routing is done as usual. > > > > Full details of the above is available here > > https://github.com/qemu/qemu/commit/2b05705dc8ad80c09a3aa9cc70c14f > > b8323b0fd3 > > > > Hope this answers your question. > > > I took cursory look. I am almost sure that if guest VM's IP address is not added to host, modify_qp() in kernel is going to fail. Unless you use a different GID in host. And build some smart way to figure out which one to use. The option to use different GID is too complex and even not applicable as you have to make the fabric know to route traffic to it. Check the above step #3, the guest GID (and so also IP) is pops up to the host level. > > > >
