[Qemu-devel] Question about RNG virtio device

[Dennis Chen <dennis.chen@arm.com>]

Hello QEMU developers,

We all know that there is a virtio-rng device can be para-virtualised from
the host to guest in case of a real RNG HW exists in the host, my question
is:
Can we get some performance gain to use the 'virtio-rng' device if there isn't
a real RNG HW in host, in this case, what's the default back-end of the virtio
-rng device?
For my scenario, I don't want to use a virtio-rng device if the host doesn't have
a RNG HW, because the guest will get a fake RNG HW with virtio-rng device (/sys/
devices/virtual/misc/hw_random/rng_current), which is not expected. But if 
virtio-rng is not used, I don't know how the guest get the entropy from the host,
the most concern is performance. IOW, what's the difference between virtio-rng used
and not if there isn't a RNG HW in host?

Thanks!