linux-kernel - Re: [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit

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Message-Id: <1204311412.28554.1239873349@webmail.messagingengine.com>
Date:	Fri, 29 Feb 2008 19:56:52 +0100
From:	"Alexander van Heukelum" <heukelum@...tmail.fm>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Mark McLoughlin" <markmc@...hat.com>,
	"Alexander van Heukelum" <heukelum@...lshack.com>,
	"Ingo Molnar" <mingo@...e.hu>, "Ian Campbell" <ijc@...lion.org.uk>,
	"Andi Kleen" <ak@...e.de>, "Thomas Gleixner" <tglx@...utronix.de>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>,
	"LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] reserve end-of-conventional-memory to 1MB on 32-bit


On Fri, 29 Feb 2008 10:44:36 -0800, "H. Peter Anvin" <hpa@...or.com>
said:
> Alexander van Heukelum wrote:
> > 
> > My first guess is that the BIOS data area is completely non-existent for
> > Xen.
> > Is it guaranteed that the memory is zeroed out on boot? In that case we
> > can
> > special-case it easily:
> > 
> > change:
> >         /* Paranoia: should never happen, but... */
> >         if (lowmem >= 0x100000)
> >                 lowmem = 0xa0000;
> > 
> > into:
> >         /* Strange case, like Xen ;) */
> >         if (lowmem == 0 || lowmem >= 0x100000)
> >                 lowmem = 0x9f000;
> > 
> > Can you test that?
> > 
> 
> The EBDA is optional anyway; I presume it should have a zero pointer if 
> it isn't present.

Correct, but the value that indicates the size of the conventional
memory
area must be set. At least on any real hardware. My guess is that both
values read as 0 on Xen, which causes 0-0x100000 to be reserved. If that
is always the case the workaround is fine, I think.

Alexander

> 	-hpa
-- 
  Alexander van Heukelum
  heukelum@...tmail.fm

-- 
http://www.fastmail.fm - mmm... Fastmail...

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