Should adding:

RuntimeDirectoryMode=0775
Group=qemu
UMask=0002

to /usr/lib/systemd/system/openvswitch-nonetwork.service fix this issue?

I think a better approach is to use a separate directory for the vhost_user sockets, which would require passing the -vhost_sock_dir option to ovs-vswitchd, and updating the selinux permissions. That way we could make a sgid directory where vhost sockets go.

I will look into this and have a formal proposal (in the form of patches) soon.

There is a discussion upstream at http://openvswitch.org/pipermail/dev/2015-December/062845.html regarding when and how to apply DPDK parameters to Open vSwitch. Since my solution is based on the -vhost_sock_dir option, and there's a possibility that it will need to be re-architected.

That said, the packages (which haven't been fully tested) are at:
https://copr.fedoraproject.org/coprs/aconole/qemu-kvm/
and
https://copr.fedoraproject.org/coprs/aconole/openvswitch-dpdk/

I will be testing them later today/tomorrow to see that the idea is sound, and then the implementation may need further discussion.

Aaron: how'd the testing go?

Sorry for the late response. There are issues in the initial implementation that need to be cleaned up. I will respin and update the bug with corrected patches. The solution _should_ work, but may not be a final one that upstream accepts.

I have a working set of packages, on COPR:

https://copr.fedoraproject.org/coprs/aconole/openvswitch-dpdk/
and
https://copr.fedoraproject.org/coprs/aconole/qemu-kvm/

The following are the changes that I did:

On package install:
1. QEMU adds itself to the vhost group (if no such group exists, it creates)
2. Openvswitch-DPDK adds the vhost group if it doesn't already exist

Open vSwitch DPDK package has the following changes:

ovs-ctl accepts an (not-required) option in /etc/sysconf/openvswitch called VHOST_SOCK_DIR which should be a path in the filesystem. This variable is only used when DPDK_OPTIONS are specified.

If the path specified by VHOST_SOCK_DIR does not exist, ovs-ctl creates it during openvswitch startup, and sets mode to rwxrwsr-x with a group of vhost

Once the path specified in VHOST_SOCK_DIR exists, openvswitch passes it and DPDK_OPTIONS has a value, ovs-ctl sets umask to 0002, launches ovs-vswitchd, and restores umask.

I will post the patches for Panu and Flavio to review, and then bring it to wider audience (because it may not be the solution upstream accepts).

The upstream solution is posted at 
http://openvswitch.org/pipermail/dev/2016-January/063959.html

This is the first series to reorganize under the database. The second will be to set vhost-sock permissions and ownership.