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

[Scott Wood]

On Fri, 2 Jul 2010 20:47:44 +0200
Alexander Graf <agraf at suse.de> 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).

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.

-Scott