Re: vga passthrough // questions about pci passthrough

[Martin Wolf <mwolf@adiumentum.com>]

Hello,

would a Memory Dump from inside the VM help solving the BSOD,
or is that pointless?

Thank you for your patience and help ;)


Am 28.09.2012 18:29, schrieb Jan Kiszka:
> On 2012-09-28 17:50, Alex Williamson wrote:
>> On Fri, 2012-09-28 at 10:12 +0200, Jan Kiszka wrote:
>>> On 2012-09-27 21:18, Alex Williamson wrote:
>>>> On Thu, 2012-09-27 at 20:43 +0200, Martin Wolf wrote:
>>>>> thank you for the information.
>>>>>
>>>>> i will try what you mentioned...
>>>>> do you have some additional information about rebooting a VM with a
>>>>> passed through videocard?
>>>>> (amd / ati 7870)
>>>> I don't.  Is the bsod on reboot only or does it also happen on shutdown?
>>>> There's a slim chance it could be traced by enabling debug in the
>>>> pci-assign driver and analyzing what the guest driver is trying to do.
>>>> I'm hoping that q35 chipset support might resolve some issues with vga
>>>> assignment as it exposes a topology that looks a bit more like one that
>>>> a driver would expect on physical hardware.  Thanks,
>>>  From our attempts to get more working than what NVIDIA Quadro cards
>>> support officially, my own experiments with q35 in this context and our
>>> discussions with NVIDIA, I'm pretty skeptical that this chipset will
>>> make a difference here. Most problems are due to those non-standard side
>>> channels to configure the hardware, memory mappings etc. And getting
>>> this working requires either cooperation of the vendor or *a lot* of
>>> reverse engineering.
>> I heard from an nvidia guy that the driver behaves differently depending
>> on whether it finds an upstream express port, so we're probably causing
>> ourselves more problems if it's trying to run in AGP mode.
> May be a point for the low- to mid-range cards. It does not apply to the
> "virtualization-ready" Quadro series according to our information back then.
>
>>   There was
>> also a lot of FUD in Xen (maybe justified) around how the BIOS
>> determines the memory ranges and whether it bypasses the PCI BARs and
>> gets them directly.  That means some cards may require identity mapping
>> to work.  It seems like the very high-end cards are possibly fixing
>> this, but they're far more expensive than I can justify.  Thanks,
> Yes, that is what makes them virtualization ready. But they also come
> with limitations. So far, you can't pass-through a primary card or use
> it for early boot messages of the guest as the BIOS is not ready for
> that - without identity mapping or even more.
>
> Jan
>


-- 
Adiumentum GmbH
Gf. Martin Wolf
Banderbacherstraße 76
90513 Zirndorf

0911 / 9601470
mwolf@adiumentum.com