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

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

On 07/04/2010 12:04 PM, Alexander Graf wrote:

quoted

=20
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?

=20
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?

=20

quoted

Why do I have to patch 3 projects (Linux, OpenBIOS, Qemu) when I =

could go with patching a single one (Linux)?

quoted

 =20

=20
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?

=20
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