AW: Re: __setup_cpu_be problem

[Hollis Blanchard]

On Tue, 14 Feb 2006 17:25:47 -0600, "Olof Johansson" <olof at lixom.net>
said:
> On Tue, Feb 14, 2006 at 03:14:47PM -0800, Geoff Levand wrote:
> > I guess what I am thinking of are cases like when the firmware has no
> > clue and just uses defaults, or when the firmware or hypervisor
> > expect the kernel to set what sizes work best for it.  In these
> > cases a change needs to be initiated by the kernel.
> 
> But then give the firmware a clue, and fix it. For the partitioned
> case, I'm sure you have ways for an alpha partition to define the
> characteristics of a guest partition, and/or a small controller image
> running in your hypervisor for similar purposes.
> 
> If the kernel needs to set "what works best for it", then you should
> look into some of the ELF header flag stuff that IBM pSeries firmware
> architects seems to love these days, it seems to be the preferred way
> for the OS to tell firmware/hypervisor what it wants.

The solution used with the IBM pSeries hypervisor (look for "fake_elf"
in prom_init.c, in particular the "rpa_note" part of it) is considered
poor by some kernel developers. Implementing something more
fine-grained, like a "capabilities" hcall/rtas method/whatever would
allow for much more flexibility, which makes sense since the information
we want to communicate will undoubtedly grow on future platforms.

In this case, an hcall requesting two page sizes would allow the
hypervisor to validate the request and implement it as needed on
differing hardware, whether it's via HID6 or some other
hypervisor-privileged mechanism.

-Hollis