Re: [kvm-unit-tests PATCH 11/14] powerpc/ppc64: add rtas_power_off

[Andrew Jones <drjones@redhat.com>]

On Tue, Aug 04, 2015 at 02:09:52PM +1000, David Gibson wrote:
> On Mon, Aug 03, 2015 at 07:08:17PM +0200, Paolo Bonzini wrote:
> > 
> > 
> > On 03/08/2015 16:41, Andrew Jones wrote:
> > > Add enough RTAS support to support power-off, and apply it to
> > > exit().
> > > 
> > > Signed-off-by: Andrew Jones <drjones@redhat.com>
> > 
> > Why not use virtio-mmio + testdev on ppc as well?  Similar to how we're
> > not using PSCI on ARM or ACPI on x86.
> 
> Strange as it seems, MMIO is actually a PITA for a simple pseries
> guest like this.  Basically, you have to enable the MMU - which
> requires a whole bunch of setup - in order to perform cache-inhibited
> loads and stores, which is what you need for IO.
> 
> There are hypercalls to sidestep this (H_LOGICAL_CI_LOAD and
> H_LOGICAL_CI_STORE), but having a hypercall and KVM exit for every IO
> access may be hideously slow.
> 
> In early development we did have a hypercall mediated virtio model,
> but it was abandoned once we got PCI working.

So I think by yours and Alex's responses, if we want testdev support
then we should target using pci to expose it. I'm ok with that, but
prefer not to be distracted with it while getting ppc kickstarted.
So, question for Paolo, are you OK with the exitcode snooper "cheat"?

Thanks,
drew

> 
> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson