Re: [Qemu-devel] Re: [PATCH 2/3] qemu: make cirrus init value pci spec compliant

[Kevin O'Connor]

On Mon, Oct 12, 2009 at 08:44:56AM -0500, Anthony Liguori wrote:
> Gleb Natapov wrote
>>> BTW, I don't think it's write-protected and it probably should be?
>>>
>>>     
>> AFAIR it is not writable on plain qemu.
>>   
>
> KVM wants it to be writable for the TPR optimization.  Historically, it  
> was read-only in QEMU but it changed to read-write in order to fake  
> coreboot into thinking that the bios implemented PMM which it doesn't.

During init, SeaBIOS will enable writes to all memory between
0xc0000-0x100000 - shadowing the ram as needed.  Just prior to
starting the boot phase, SeaBIOS will make the bios f-segment and all
option roms read only.  (Note, this differs from bochs-bios which
doesn't make optionroms writable - seabios makes them writable because
some optionroms need it.)

As an aside, it would be nice if qemu would just start off with this
memory as read/writable, as the shadoing process is ugly, it's qemu
specific, and it always ends up as read/writable anyway.

I'm not sure where coreboot or PMM comes into this.  SeaBIOS does
implement the Post Memory Manager calls.

-Kevin