Re: [PATCH 27/27] KVM: PPC: Add Documentation about PV interface

Alexander Graf
2010-07-04T09:02:16Z

On 02.07.2010, at 21:10, Scott Wood wrote:

> On Fri, 2 Jul 2010 20:47:44 +0200
> Alexander Graf <agraf-l3A5Bk7waGM@public.gmane.org> wrote:
>
>>
>> On 02.07.2010, at 19:59, Hollis Blanchard wrote:
>>
>>> [Resending...]
>>>
>>> Please reconcile this with
>>> http://www.linux-kvm.org/page/PowerPC_Hypercall_ABI, which has been
>>> discussed in the (admittedly closed) Power.org embedded hypervisor
>>> working group. Bear in mind that other hypervisors are already
>>> implementing the documented ABI, so if you have concerns, you should
>>> probably raise them with that audience...
>>
>> We can not use sc with LV=1 because that would break the KVM in
>> something else case which is KVM's strong point on PPC.
>
> The current proposal involves the hypervisor specifying the hcall opcode
> sequence in the device tree -- to allow either "sc 1" or "sc 0 plus
> magic GPR" depending on whether you've got the hardware hypervisor
> feature (hereafter HHV).

Ah right, so you can still trap a hypercall with HHV. Makes sense.

>
> With HHV, "sc 0 plus magic GPR" just doesn't work, since it won't trap
> to the hypervisor. "sc 1 plus magic GPR" might be problematic on some
> non-HHV implementations, especially if you *do* have HHV but the
> non-HHV hypervisor is running as an HHV guest.

Yes, that's why I need sc 0 plus magic GPR in r0 and r3 - to accomodate for all the non-HHV cases. And it would be clever to have a way to expose the same functionality when we do use the HHV features.

So, is that draft available anywhere? The wiki page Hollis pointed to is very vague.

Alex