linux-kernel - Re: how to tell linux (on x86) to ignore 1M or memory

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Date:	Fri, 20 Apr 2007 23:39:54 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Rene Herman <rene.herman@...il.com>, Dave Jones <davej@...hat.com>,
	Neil Brown <neilb@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kyle McMartin <kyle@...onical.com>,
	linux-kernel@...r.kernel.org, alan@...hat.com, bcollins@...ntu.com,
	pjones@...hat.com
Subject: Re: how to tell linux (on x86) to ignore 1M or memory

Rene Herman <rene.herman@...il.com> wrote:
> On 04/19/2007 04:18 PM, Bart Trojanowski wrote:

>> I need to preserve some state from the bios before entering protected
>> mode.  For now I want to copy it into some ram accessible by real-mode,
>> say the last megabyte visible in real-mode.
>> 
>> What's the easiest way to have linux ignore the megabyte starting at 15M?
> 
> Note that real-mode can only access the first megabyte (*) and not the first
> 16. 16MB is the 16-bit protected mode (286) limit.
> 
> (*) well, the first 1M + 64K - 16 bytes using segment FFFF assuming A20 is
> enabled and x > 1 in x86...

Interrupt 15h, function 87h allows copying from/to extended memory.
You might like to look into Ralph Brown's interrupt list for more details.

You could also cpio-gzip the data and append it to the initramfs.
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