From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1NCEW4-0006Yn-Ra
	for qemu-devel@nongnu.org; Sun, 22 Nov 2009 10:38:20 -0500
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1NCEW0-0006Vi-3i
	for qemu-devel@nongnu.org; Sun, 22 Nov 2009 10:38:20 -0500
Received: from [199.232.76.173] (port=60256 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1NCEVz-0006VZ-VS
	for qemu-devel@nongnu.org; Sun, 22 Nov 2009 10:38:16 -0500
Received: from mx1.redhat.com ([209.132.183.28]:5527)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <gleb@redhat.com>) id 1NCEVz-0007PV-GK
	for qemu-devel@nongnu.org; Sun, 22 Nov 2009 10:38:15 -0500
Date: Sun, 22 Nov 2009 17:38:09 +0200
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios
Message-ID: <20091122153809.GL3193@redhat.com>
References: <B40ED509E5954950B7AB28E7FBBF450C@FSCPC>
	<20091120225113.GD24539@morn.localdomain>
	<20091122123503.GH3193@redhat.com>
	<E9BAFA7165DD41AFA62959CAEFFC2A63@FSCPC>
	<20091122151052.GK3193@redhat.com>
	<217FD12D88EA4AC2B2A32D77E010B16C@FSCPC>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <217FD12D88EA4AC2B2A32D77E010B16C@FSCPC>
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Sebastian Herbszt <herbszt@gmx.de>
Cc: Kevin O'Connor <kevin@koconnor.net>, qemu-devel@nongnu.org

On Sun, Nov 22, 2009 at 04:31:24PM +0100, Sebastian Herbszt wrote:
> Gleb Natapov wrote:
> >On Sun, Nov 22, 2009 at 04:07:56PM +0100, Sebastian Herbszt wrote:
> >>Gleb Natapov wrote:
> >>>May be make qemu to map it writable if isapc is specified.
> >>
> >>I don't think keeping the segment writable after POST is a good idea.
> >>
> >Isn't it writable now after POST with pcipc? Why this is not a good
> >idea?
> 
> seabios got this in src/post.c:
>    // Allow writes to modify bios area (0xf0000)
>    make_bios_writable();
>    // Perform main setup code.
>    post();
> ...
>    // Write protect bios memory.
>    make_bios_readonly();
Hmmm. How is tpr patching works then? It relies on ability of a guest to
write into BIOS memory region. Need to retest if it actually works I
guess.

> 
> The names and comments are kind of misleading since make_bios_writable()
> and make_bios_readonly() both seem to also affect the option roms.
> 
> Bad things could happen if someone modifies the BIOS because it's unprotected
> (e.g. VM crash).
> 
BIOS is reloaded during VM reset.

--
			Gleb.