ARM processor mode, kernel startup, Hyp / secure state

[Will Deacon]

On Wed, Aug 24, 2011 at 05:09:01PM +0100, Ian Jackson wrote:
> Will Deacon writes ("Re: ARM processor mode, kernel startup, Hyp / secure state"):
> > The next step is to define our interface to the HVC trampoline. I think it
> > would be good if this interface could be reused by vendors who provide their
> > own hypervisor layer as this would reduce the need for lots of distinct HVC
> > APIs that essentially all do the same thing. It might be a good idea to
> > `reserve' a high region of the HVC space for use by Linux rather than index
> > the calls from 0, for example, which is likely to conflict with other
> > hypervisor implementations. I think the trampoline only needs a handful of
> > HVC calls (if that) anyway.
> > 
> > What do you reckon?
> 
> I think the trampoline needs to have one hypercall: "set HVBAR".
> (And, implicitly, it needs to be specified that the resulting vectors
> will run without physical-to-virtual page translation, etc.)  That is
> sufficient to bootstrap all the rest of the way up - and that other
> bootstrapping code would have to exist anyway.

I also thought you might want a hypercall that gives you a version number
(i.e. a way to identify the hypervisor trampoline in case it changes) and we
might also want something for doing a system reset (for example, if a kernel
that hasn't installed a hypervisor wants to kexec another kernel image).

> So I'm imagining that the kvm kernel module would, when loaded,
> make that "set HVBAR" once on each cpu, replacing the trampoline
> hypervisor with its own set of hypercall vectors.

That's the plan!

Will