Re: Advice on HYP interface for AsyncPF

[Marc Zyngier <marc.zyngier@arm.com>]

On Thu, 9 Apr 2015 02:46:54 +0100
Mario Smarduch <m.smarduch@samsung.com> wrote:

Hi Mario,

> I'm working with AsyncPF, and currently using
> hyp call to communicate guest GFN for host to inject
> virtual abort - page not available/page available.
> 
> Currently only PSCI makes use of that interface,
> (handle_hvc()) can we overload interface with additional
> hyp calls in this case pass guest gfn? Set arg0
> to some range outside of PSCI use.

I can't see a reason why we wouldn't open handle_hvc() to other
paravirtualized services. But this has to be done with extreme caution:

- This becomes an ABI between host and guest
- We need a discovery protocol
- We need to make sure other hypervisors don't reuse the same function
  number for other purposes

Maybe we should adopt Xen's idea of a hypervisor node in DT where we
would describe the various services? How will that work with ACPI?

Coming back to AsyncPF, and purely out of curiosity: why do you need a
HYP entry point? From what I remember, AsyncPF works by injecting a
fault in the guest when the page is found not present or made
available, with the GFN being stored in a per-vcpu memory location.

Am I missing something obvious? Or have I just displayed my ignorance on
this subject? ;-)

Thanks,

	M.
-- 
Without deviation from the norm, progress is not possible.