rxhash for virtio_net

While trying to enable rxhash for virtio_net over net-next, I found
that we still do not support it. Quick Google search yields several
patches (including flow-director for virtio_net), but looks like none
of them made it in. If my observation is correct, what are the
prominent reasons why rxhash support for virtio has not made its way
in ? (I see some concerns over Out-of-order delivery etc, any other ?
). Without rxhash for virtio, is there a way to tie a flow to a
particular cpu on host and guest side ?

Thanks,
N