Re: Re: [PATCH][RFC] gfx_passthru: warning when vgabios rom has invalid checksum

[Weidong Han <weidong.han@intel.com>]

Noboru Iwamatsu wrote:
> Hi Weidong,
>
>  > How did you recalculate it? is it possible to recalculate it when detect
>  > invalid checksum?
>
> Checking and recalculating the VGABIOS checksum is being processed
> in setup_vga_pt() in hw/pass-through.c.
> I thought you have written that part.
>
> If the checksum is invalid, current setup_vga_pt() always overwrites
> it with the recalculated value.
>
> What I mention is: the VGABIOS checksum must have been already
> recalculated by system BIOS. So, when setup_vga_pt() detects the
> invalid one, something might be wrong.
>
> But, I'm not sure all BIOS should work as described in PCIFW Spec.
> Actually, my Q35 had invalid checksum.
>   
Now I understand. Because your Q35 works with recalculated checksum, I 
prefer to only add a warning message, and continue to load rom for gfx 
passthru.

Regards,
Weidong
>
> I attach another patch:
> This stops loading vgabios if the checksum is wrong.
>
> Signed-off-by: Noboru Iwamatsu <n_iwamatsu@jp.fujitsu.com>
>
>   
>> Noboru Iwamatsu wrote:
>>     
>>> Hi,
>>>
>>>       
>>>>> Intel DX58SO + GeForce GTS250: checksum is OK.
>>>>> Intel DX58SO + GeForce 9600GT: checksum is OK.
>>>>> Fujitsu Q35 M/B + IGD: checksum is bad.
>>>>>
>>>>>           
>>>> What does "checksum is bad" mean here?
>>>>         
>>> It means shadowed VGABIOS has invalid checksum
>>> and requires recalculating.
>>>
>>>       
>>>>> What do you think, Weidong?
>>>>> Is just warning enough? Or, should we stop loading the rom?
>>>>>
>>>>>
>>>>>           
>>>> Does it still work or not when checksum is bad? If it works, we should
>>>> not stop loading the rom.
>>>>         
>>> When the checksum is bad,
>>> if it is not recalculated, guest has some trouble about handling the
>>> VGA (unable to show BIOS screen, unable to load the gfx driver
>>> properly, ...).
>>>       
>> For this case, it's reasonable to warning and stop loading rom. We
>> didn't encounter this issue.
>>     
>>> If it is recalculated, it seems to work fine.
>>>       
>> How did you recalculate it? is it possible to recalculate it when detect
>> invalid checksum?
>>
>> Regards,
>> Weidong
>>
>>     
>>> Regards,
>>> Noboru.
>>>
>>>       
>>>> Noboru Iwamatsu wrote:
>>>>         
>>>>> Hi,
>>>>>
>>>>> According to the "PCI Firmware Spec Rev 3.0",
>>>>> the system firmware have to write the new checksum after resizing
>>>>> the expansion ROM area.
>>>>>
>>>>> So, when re-using the shadowed VGABIOS, the checksum must
>>>>> be valid, and if it is invalid, we should consider the BIOS has
>>>>> a bug or memory area is corrupted.
>>>>>
>>>>> This patch just add the warning message when checksum requires
>>>>> recalculation.
>>>>>
>>>>> I tried this following environments.
>>>>>
>>>>> Intel DX58SO + GeForce GTS250: checksum is OK.
>>>>> Intel DX58SO + GeForce 9600GT: checksum is OK.
>>>>> Fujitsu Q35 M/B + IGD: checksum is bad.
>>>>>
>>>>>           
>>>> What does "checksum is bad" mean here?
>>>>         
>>>>> What do you think, Weidong?
>>>>> Is just warning enough? Or, should we stop loading the rom?
>>>>>
>>>>>
>>>>>           
>>>> Does it still work or not when checksum is bad? If it works, we should
>>>> not stop loading the rom.
>>>>
>>>> Regards,
>>>> Weidong
>>>>         
>>>>> Regards,
>>>>> Noboru.
>>>>>
>>>>>           
>>>       
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>
>