Thankfully, better designs such as seL4's VMM do exist, although it might need a little more work [1] until usable for the purpose.
https://groups.google.com/forum/m/#!topic/qubes-devel/jEe4pQ...
> It seems one major residing problem with KVM is the Linux kernel (which is large and vulnerable). A port of KVM to a thinner base layer would obviate those issues.