linux-kernel - Re: [PATCH 04/14] x86, ACPI: make acpi override finding work with 32bit flat mode

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Date:	Thu, 7 Mar 2013 23:28:46 -0800
From:	Tejun Heo <tj@...nel.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	"Yu, Fenghua" <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, "H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Renninger <trenn@...e.de>,
	Tang Chen <tangchen@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Pekka Enberg <penberg@...nel.org>,
	Jacob Shin <jacob.shin@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH 04/14] x86, ACPI: make acpi override finding work with
 32bit flat mode

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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