libvirt users - Jun 2014 - kvm domain won't start with vhost-net loaded

Hi,

I have multiple kvm domains running fine, but to improve network
performance, I wanted to try vhost-net. However, once I load the module:

modprobe vhost-net

I can't start the domain anymore:
  virsh start kvmGitInt
gives the error:
internal error: process exited while connecting to monitor:
qemu-system-x86_64: -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=26:
vhost-net requested but could not be initialized
qemu-system-x86_64: -netdev tap,fd=25,id=hostnet0,vhost=on,vhostfd=26:
Device 'tap' could not be initialized

This is a 3.14.4 kernel, with libvirt 1.2.1 and qemu 1.7.0.

I have searched online but haven't found any indication on how to solve it
in my case (The kernel is not selinux enabled,not using systemd, ...)

Any suggestion on how to solve this is very welcome!

Thanks in advance

Raph
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