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From: "Sebastian Herbszt" <herbszt@gmx.de>
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Subject: Re: [Qemu-devel] Re: POST failure (loop) with isapc and seabios
Date: Sun, 22 Nov 2009 16:31:24 +0100
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To: Gleb Natapov <gleb@redhat.com>
Cc: Kevin O'Connor <kevin@koconnor.net>, qemu-devel@nongnu.org

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();

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).

- Sebastian