Custom BIOS supported size

Custom BIOS supported size

[Cristi Magherusan]

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Hello,

Which is the maximum size supported for a custom BIOS image(eg.
coreboot-based)? I tried some 256K coreboot BIOS images and seemed to
work fine, but it blowed up with a 3MB image (which by the way works on
qemu just fine). 

Qemu also seems to fail with images greater than 4MB, and I'd appreciate
if either kvm or qemu had support for such images, and maybe even
greater than that if technically possible.

You can get such images from http://www.coreboot.org/QEMU
The 3MB one that I tried can be fetched from
http://panzer.utcluj.ro/~alien/coreboot/AVATT/BIOS/OpenVZ/bios.bin

Thanks!
Cristi

-- 
Ing. Cristi Măgherușan, System/Network Engineer
Technical University of Cluj-Napoca, Romania
http://cc.utcluj.ro  +40264 401247

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Re: Custom BIOS supported size

[Avi Kivity]

Cristi Magherusan wrote:
> Hello,
>
> Which is the maximum size supported for a custom BIOS image(eg.
> coreboot-based)? I tried some 256K coreboot BIOS images and seemed to
> work fine, but it blowed up with a 3MB image (which by the way works on
> qemu just fine). 
>   

256K is the maximum with kvm.  It can easily be increased, but we need a 
small kernel change on Intel to store the real-mode TSS.




-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

Re: Custom BIOS supported size

[Cristi Magherusan]

On Mon, 2009-05-04 at 16:48 +0300, Avi Kivity wrote:
> Cristi Magherusan wrote:
> > Hello,
> >
> > Which is the maximum size supported for a custom BIOS image(eg.
> > coreboot-based)? I tried some 256K coreboot BIOS images and seemed to
> > work fine, but it blowed up with a 3MB image (which by the way works on
> > qemu just fine). 
> >   
> 
> 256K is the maximum with kvm.  It can easily be increased, but we need a 
> small kernel change on Intel to store the real-mode TSS.
> 
> 
Hi Avi,

Thanks for your answer. What would be the upper bound up to which we can
extend it? May I somehow help in getting this done?

Best regards,
Cristi

-- 
Ing. Cristi Măgherușan, System/Network Engineer
Technical University of Cluj-Napoca, Romania
http://cc.utcluj.ro  +40264 401247

Re: Custom BIOS supported size

[Avi Kivity]

Cristi Magherusan wrote:
> On Mon, 2009-05-04 at 16:48 +0300, Avi Kivity wrote:
>   
>> Cristi Magherusan wrote:
>>     
>>> Hello,
>>>
>>> Which is the maximum size supported for a custom BIOS image(eg.
>>> coreboot-based)? I tried some 256K coreboot BIOS images and seemed to
>>> work fine, but it blowed up with a 3MB image (which by the way works on
>>> qemu just fine). 
>>>   
>>>       
>> 256K is the maximum with kvm.  It can easily be increased, but we need a 
>> small kernel change on Intel to store the real-mode TSS.
>>
>>
>>     
> Hi Avi,
>
> Thanks for your answer. What would be the upper bound up to which we can
> extend it? May I somehow help in getting this done?
>   

I don't know all the places; check the setup code in hw/pc.c.  Also look 
at the call to KVM_SET_TSS_ADDR and move it somewhere where it won't 
clash (right now it's at 4GB-256K).


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.