Look into to your /dev directory and see who can write /dev/kvm.

(If you don't see /dev/kvm special file, look into kernel logs via dmesg command. If you see "KVM is disabled by BIOS", go to your BIOS setup and enable hardware virtualization, otherwise you VM performance would suffer painfully)

Typically /dev/kvm is writable to kvm group.

So, only members of this group would be able to start virtual machines with hardware virtualization.

You should make all living users who want to run virtual machines, members of this group.