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

Alexander Graf
2010-07-04T09:17:47Z

On 04.07.2010, at 11:10, Avi Kivity wrote:

> On 07/04/2010 12:04 PM, Alexander Graf wrote:
>>
>> My biggest concern about putting things in the device-tree is that I was trying to keep things as separate as possible. Why does the firmware have to know that it's running in KVM?
>
> It doesn't need to know about kvm, it needs to know that a particular hypercall protocol is available.

Considering how the parts of the draft that I read about sound like, that's not the inventor's idea. PPC people love to see the BIOS be part of the virtualization solution. I don't. That's the biggest difference here and reason for us going different directions.

I think what they thought of is something like

if (in_kvm()) {
device_tree_put("/hypervisor/exit", EXIT_TYPE_MAGIC);
device_tree_put("/hypervisor/exit_magic", EXIT_MAGIC);
}

which then the OS reads out. But that's useless, as the hypercalls are hypervisor specific. So why make the detection on the Linux side generic?

>
>> Why do I have to patch 3 projects (Linux, OpenBIOS, Qemu) when I could go with patching a single one (Linux)?
>>
>
> That's not a valid argument. You patch as many projects as it takes to get it right (not that I have an opinion in this particular discussion).

If you can put code in Linux that touches 3 submaintainer's directories or one submaintainer's directory with both ending up being functionally equivalent, which way would you go?

>
> At the very least you have to patch qemu for reasons described before (backwards compatible live migration).

There is no live migration on PPC (yet). That point is completely moot atm.

Alex