virtio crypto device implemenation

Hi, Michael, 
   As you know, Lei Gong from Huawei and I are co-working  on virtio crypto device spec, he is focusing on symmetric algorithm part, I am focusing on asymmetric part.  Now I am planning the implementation for asymmetric part, would you please give me your point regarding the questions below?
   Current virtio crypto device implementation from Lei Gong:
   The virtio crypto device implementation has been upstreamed to QEMU and it has a qemu backend implementation for symmetric algorithm part, the front end Linux device driver for symmetric part has been upstreamed to Linux kernel as well.
   My questions:
   From my side, I planned to add the asymmetric part support in upstreamed front end device driver, and I don't want to add the asymmetric algorithm support to current virtio crypto device's qemu backend, instead, I would like to implement and upstream a DPDK vhost-user based backend for asymmetric algorithm, and accordingly Lei Gong will help to upstream a vhost user agent for virtio crypto device in QEMU,  is this approach acceptable? Is a qemu backend a mandatory requirement for the virtio crypto device?  Is there a general policy for this?

Thanks