Re: [libvirt] NFS over AF_VSOCK in <filesystem>

On Thu, May 19, 2016 at 10:27:17AM +0100, Daniel P. Berrange wrote: > On Mon, May 16, 2016 at 04:58:48PM -0700, Stefan Hajnoczi wrote: > > On Wed, May 11, 2016 at 03:42:34PM +0100, Daniel P. Berrange wrote: > > > On Tue, May 10, 2016 at 01:03:48PM +0100, Stefan Hajnoczi wrote: > > > > On Mon, May 09, 2016 at 05:18:42PM +0100, Daniel P. Berrange wrote: > > > > > On Mon, May 09, 2016 at 04:57:17PM +0100, Stefan Hajnoczi wrote: > > > > > > virtio-vsock support has been added to the nfs-ganesha NFS server. I'm > > > > > > currently working on upstreaming virtio-vsock into Linux and QEMU. I > > > > > > also have patches for the Linux NFS client and server. > > > > > > > > > > > > Users wishing to share a file system with the guest will need to > > > > > > configure the NFS server. Perhaps libvirt could handle that given that > > > > > > it already has <filesystem> syntax. > > > > > > > > > > > > The basic task is setting up either the kernel nfsd or nfs-ganesha for > > > > > > the VM to access the NFS export(s). When the VM is destroy the NFS > > > > > > server can be shut down. > > > > > > > > > > Can you elaborate on the interaction between QEMU and the NFS server > > > > > on the host ? What actually needed changing in nfs-ganesha to support > > > > > virtio-vsock ? I thought that on the host side we wouldn't need any > > > > > changes, because QEMU would just talk to a regular NFS server over > > > > > TCP, and the only virtio-vsock changes would be in QEMU and the guest > > > > > kernel. > > > > > > > > The NFS protocol (and SUNRPC) is aware of the transport its running > > > > over. In order to fully support the protocol it needs to know about > > > > AF_VSOCK and addressing. > > > > > > > > The NFS server changes allow specifying an AF_VSOCK listen port. The > > > > machine name format in /etc/exports or equivalent config also needs to > > > > support vsock. > > > > > > So from host POV, in our current model of exposing host FS to the guest > > > where libvirt wants control over managing exports, I don't think we > > > would be inclined to use the in-kernel NFS server at all, nor would we > > > likely use the main system ganesha server instance. > > > > > > Instead what I think we'd want is to run an isolated instance of ganesha > > > for each QEMU VM that requires filesystem passthrough. First of all this > > > removes any unpredictability around setup, as arbitrary admin config > > > changes to the default system ganesha server would not conflict with > > > settings libvirt needed to make for QEMU. Second it would let us place > > > the ganesha server associated with a VM in the same cgroup, so we can > > > ensure resources limits associated with the VM get applied. Third it > > > would let us apply the per-VM svirt MCS level to each ganesha, to > > > ensure that there's no risk of cross-VM attack vectors via the > > > ganesha services. Ideally QEMU would talk to ganesha over a private > > > UNIX domain socket though it looks like ganesha only has the ability > > > to use TCP or UDP right now, so that'd be something we need to add > > > support for. > > > > virtio-vsock uses a vhost kernel module so that traffic comes from the > > host's network stack, not from QEMU. So there wouldn't be a unix domain > > socket connecting the VM to ganesha (although something along those > > lines could be implemented in the future). > > Hmm, are there any docs explaining the virtio-vsock architecture/setup > in a bit more detail ? It feels some undesirable for the vsock backend > to be directly connected to the host network - feels like it would be > opening avenues for attacking the host network services. Only AF_VSOCK host network services would be listening. Today there are none.

There are no docs yet but it's pretty much the same as VMware vSockets (which shares the AF_VSOCK address family and some of the code with virtio-vsock). The VMware guide covering sockets usage is here: https://pubs.vmware.com/vsphere-60/topic/com.vmware.ICbase/PDF/ws9_esx60_...