Problem

Cryptographic key creation (GnuPG, SSH, etc.) in virtual guests may be very slow because there is not enough entropy.

$ cat /proc/sys/kernel/random/entropy_avail 
7

Solution

Add /dev/urandom from virtual host in virt-manager. Click on "Add Hardware".

Add "RNG" device.

This is what will be added to the qemu xml file in /etc/libvirt/qemu:

<domain type='kvm'>
  ---
  <devices>
    ...
   <rng model='virtio'> 
     <backend model='random'>/dev/urandom</backend> 
     <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/> 
   </rng> 
 </devices> 
</domain>

In the virtual guest, install "rng-tools" (Ubuntu 18.04).

$ sudo apt-get install rng-tools

If something goes wrong, the rngd daemon will complain in /var/log/syslog.

Oct 13 22:48:07 guest rngd: read error 
Oct 13 22:48:07 guest rngd: message repeated 99 times: [ read error] 
Oct 13 22:48:07 guest rngd: No entropy sources working, exiting rngd

If rngd is working correctly, check entropy level again.

$ cat /proc/sys/kernel/random/entropy_avail
3162