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

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Date:	Tue, 31 Oct 2006 16:01:10 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Jun Sun <jsun@...sun.net>
Cc:	"Richard B. Johnson" <jmodem@...minablefirebug.com>,
	linux-kernel@...r.kernel.org
Subject: Re: reserve memory in low physical address - possible?

Ar Maw, 2006-10-31 am 07:40 -0800, ysgrifennodd Jun Sun:
> On Tue, Oct 31, 2006 at 07:32:37AM -0500, Richard B. Johnson wrote:
> > 
> > You will not be able to reserve any address space starting at 0 anyway, but 
> > your driver or even
> > user-space code can memory-map it.
> > 
> 
> Any reasons or concerns as to why I can't reserve any address space 
> starting from 0?

None at all, Richard is wrong on this point. You can happily reserve
memory starting at physical zero on an x86. In fact the x86 kernel
*already* does this because many BIOSes use the first page for BIOS data
and touch it when we use BIOS services or in SMM.

For a worked example of loading Linux under a small RTOS take a look at
RTLinux, which turns Linux into on task running on a tiny strict RT
kernel.

Alan

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