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

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Aug 04, 2015 at 09:47:59AM +0200, Andrew Jones wrote:
> 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.

Um.. maybe.  I'm not really familiar with these testdevs, so I can't
answer directly.

> 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"?

If you wanted to add a special hypercall channel for use by the tests
I'd be ok with that too.

-- 
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

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