Virtualization layers (was: Constant Stack Canaries)

Given 4 layers in the stack {Secure, Hyper, Super, User} and we have
interrupts targeting {Secure, Hyper, Super}, do we pick up any liability
or do we gain flexibility by being able to target interrupts directly to
{user} ?? (the 4th element).

All these discussions seem to presume a very fixed structure that (I
presume) corresponds to a typical situation in servers nowadays.

But shouldn't the hardware aim for something more flexible to account
for other use cases?

E.g. What if I want to run my own VM as a user?  Or my own HV?
That's likely to be a common desire for people working on the
development and testing of OSes and HVs?


        Stefan