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Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios

From: Gleb Natapov
Subject: Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios
Date: Sun, 22 Nov 2009 17:38:09 +0200

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

> 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.


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