I've written previously about random numbers in virtual machines. KVM still remains the only hypervisor to offer an RNG device to guests.
Quite a lot of exciting changes have landed in the upstream Linux kernel since that last post. I have written an article in the RHEL blog about it: Red Hat Enterprise Linux Virtual Machines: Access to Random Numbers Made Easy.
That articles talks about the improvements in the recent RHEL 7.1 release. In upstream terms, all the changes written about have landed in kernel 3.17; so Fedora 21 out-of-the-box, and Fedora 20 after updates, have benefited from the additions.
All the benefits listed in the article apply to all Linux guest VMs running under KVM if they have the virtio-rng device enabled, and run kernel 3.17+ in the guest.