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

Alexander Graf agraf at suse.de
Sun Jul 4 19:17:47 EST 2010

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.


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