Enabling Virtual Machine support

[Michael ODonnell]

I have fairly deep OS-level experience (including some Virtual Machine
work) but I confess that I'm not up on the very latest VM technology
so to further the discussion let me ask something that may also have
occurred to others:

   What is it in the nature of VM support in these processors (or
   possibly in the motherboards/platforms in question) that leads
   to talk about the BIOS somehow having control over whether VM
   is enabled?

I'm asking this because in my experience the typical BIOS is essentially
the boot loader and although it is written by folks with detailed
proprietary knowledge of the specific platform in question it is not
otherwise somehow more "privileged" than any OS code that it might load.

So if VM support is enabled by flipping some bit(s) in some CPU Control
Register(s) I'd assume that a VM-capable OS could flip those bits as
well as any BIOS code.  I suppose it's possible that the CPU might first
insist on seeing a certain logic level on a certain input pin before
allowing VM support to be enabled, and only the BIOS authors might know
how to poke the appropriate values into some secret I/O port to do that,
but in principle the OS would still be capable of doing that if only
those magic locations and values were known, yes?

I, too, would be irritated if I discovered that my mobo designers or
BIOS authors had decided that I was not entitled to enable a perfectly
usable feature that my CPU supported...   >-/