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

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

On Fri, 2 Jul 2010 20:47:44 +0200
Alexander Graf [off-list ref] wrote:
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quoted

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On 02.07.2010, at 19:59, Hollis Blanchard wrote:
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quoted

[Resending...]
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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...

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We can not use sc with LV=3D1 because that would break the KVM in
something else case which is KVM's strong point on PPC.

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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.

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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