Re: graphics card pci passthrough success report

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2012-09-13 07:55, Gerd Hoffmann wrote:
>   Hi,
> 
>> - Apply the patches at the end of this mail to kvm and SeaBIOS to
>>   allow for more BAR space under 4G.  (The relevant BARs on the
>>   graphics cards _are_ 64 bit BARs, but kvm seemed to turn those
>>   into 32 bit BARs in the guest.)
> 
> Which qemu/seabios versions have you used?
> 
> qemu-1.2 (+ bundled seabios) should handle that just fine without
> patching.  There is no fixed I/O window any more, all memory space above
> lowmem is available for pci, i.e. if you give 2G to your guest
> everything above 0x80000000.
> 
> And if there isn't enougth address space below 4G (if you assign lot of
> memory to your guest so qemu keeps only the 0xe0000000 - 0xffffffff
> window free) seabios should try to map 64bit bars above 4G.
> 
>> - Apply the hacky patch at the end of this mail to SeaBIOS to
>>   always skip initialising the Radeon's option ROMs, or the VM
>>   would hang inside the Radeon option ROM if you boot the VM
>>   without the default cirrus video.
> 
> A better way to handle that would probably be to add an pci passthrough
> config option to not expose the rom to the guest.

-device pci-assign,option-rom=,...

> 
> Any clue *why* the rom doesn't run?

Maybe because we are not passing through the legacy VGA I/O ranges,
maybe because the card is accessing one of the famous side channels to
configure its mappings, and we do not virtualize them (as we usually do
not know them).

Jan

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