linux-kernel - Re: reserve memory in low physical address

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Message-ID: <20061031150612.GA14272@srv.junsun.net>
Date:	Tue, 31 Oct 2006 07:06:12 -0800
From:	Jun Sun <jsun@...sun.net>
To:	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org
Subject: Re: reserve memory in low physical address - possible?

On Tue, Oct 31, 2006 at 05:12:39PM +0900, Paul Mundt wrote:
> On Mon, Oct 30, 2006 at 11:22:03PM -0800, Jun Sun wrote:
> > I understand it is possible to reserve some memory at the end by
> > specifying "mem=xxxM" option in kernel command line.  I looked into
> > "memmap=xxxM" option but it appears not helpful for what I want.
> > 
> memmap takes multiple arguments, including the start address for the
> memory map. You could also bump min_low_pfn manually if memmap= isn't
> suitable for you, something like:
> 
> 	magic_space = PFN_UP(init_pg_tables_end);
> 	min_low_pfn = magic_space + magic_size;
> 
> (assuming magic_size is rounded up already), should work fine. Though
> memmap= already takes care of most of this for you, could you explain why
> it's unsuitable?

That is fair question. I got that conclusion by a quick test with
"memmap=" and kernel did not boot. :)

Now think about it, it could be because the loader  (or the real-mode
part of kernel) has not been modified to deal with the initial gap.
Can someone confirm that and give some hints on how to do this?

Thanks.

Jun
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