> From: Stefano Garzarella [mailto:sgarzare@xxxxxxxxxx] > Sent: Tuesday, November 12, 2019 11:37 AM > > > > You already mentioned that you are working on a fix for loopback > > > > here for the guest, but presumably a host could also do loopback. > > > > > > IIUC we don't support loopback in the host, because in this case the > > > application will use the CID_HOST as address, but if we are in a nested > > > VM environment we are in trouble. > > > > If both src and dst CID are CID_HOST, we should be fairly sure that this > > Is host loopback, no? If src is anything else, we would do G2H. > > > > The problem is that we don't know the src until we assign a transport > looking at the dst. (or if the user bound the socket to CID_HOST before > the connect(), but it is not very common) > > So if we are in a L1 and the user uses the local guest CID, it works, but if > it uses the HOST_CID, the packet will go to the L0. > > If we are in L0, it could be simple, because we can simply check if G2H > is not loaded, so any packet to CID_HOST, is host loopback. > > I think that if the user uses the IOCTL_VM_SOCKETS_GET_LOCAL_CID, to set > the dest CID for the loopback, it works in both cases because we return the > HOST_CID in L0, and always the guest CID in L1, also if a H2G is loaded to > handle the L2. > > Maybe we should document this in the man page. Yeah, it seems like a good idea to flesh out the routing behavior for nested VMs in the man page. > > But I have a question: Does vmci support the host loopback? > I've tried, and it seems not. Only for datagrams - not for stream sockets. > Also vhost-vsock doesn't support it, but virtio-vsock does. > > > > > > > Since several people asked about this feature at the KVM Forum, I would > like > > > to add a new VMADDR_CID_LOCAL (i.e. using the reserved 1) and > implement > > > loopback in the core. > > > > > > What do you think? > > > > What kind of use cases are mentioned in the KVM forum for loopback? > One concern > > is that we have to maintain yet another interprocess communication > mechanism, > > even though other choices exist already (and those are likely to be more > efficient > > given the development time and specific focus that went into those). To > me, the > > local connections are mainly useful as a way to sanity test the protocol and > transports. > > However, if loopback is compelling, it would make sense have it in the core, > since it > > shouldn't need a specific transport. > > The common use cases is for developer point of view, and to test the > protocol and transports as you said. > > People that are introducing VSOCK support in their projects, would like to > test them on their own PC without starting a VM. > > The idea is to move the code to handle loopback from the virtio-vsock, > in the core, but in another series :-) OK, that makes sense. Thanks, Jorgen _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
