Re: [PATCH 04/14] x86, ACPI: make acpi override finding work with32bit flat mode

From: Tejun Heo
Date: Fri Mar 08 2013 - 02:28:56 EST


On Thu, Mar 07, 2013 at 11:25:14PM -0800, Yinghai Lu wrote:
> >> > Why is this table made a stack variable? What's the benefit of doing
> >> > that?
> >>
> >> so I do need to switch global variables to phys and access it.
> >
> > I can't really understand what your response means. Can you please
> > elaborate?
>
> sorry, I missed NOT.
>
> so I do NOT need to switch global variables from kernel virtual addr
> to phys address and access it
> in 32bit flat mode.

Ah, okay, so the function is called with a completely different
address mode and so you actually want to build the table on stack so
that you don't have to flip the address mode for the global address.

> >> yes, one for 32bit from head_32.S, phys.
> >> one for 64bit from head64.c. with _va.
> >
> > head64.c can't call with phys? Why not?
>
> HPA's #PF set up page table only handle kernel low mapping address.
>
> and after reset_early_page_tables, only kernel high mapping address is
> there. and other low mapping will be supported via #PF handler.

Okay, it now makes sense. Ah.... You'll definitely need a lot of
documentation explanining what's going on.

Thanks.

--
tejun
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