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

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

[-- Attachment #1: Type: text/plain, Size: 1111 bytes --]

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.

-- 
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

[-- Attachment #2: Type: application/pgp-signature, Size: 819 bytes --]