Re: vga passthrough with qemu-xen (or qemu upstream)

[Gordan Bobic <gordan@bobich.net>]

On 01/20/2014 09:15 PM, Shakeel Butt wrote:
> On Mon, Jan 20, 2014 at 7:29 AM, Gordan Bobic <gordan@bobich.net> wrote:
>> On 2014-01-20 15:19, Shakeel Butt wrote:
>>>
>>> On Mon, Jan 20, 2014 at 5:31 AM, Gordan Bobic <gordan@bobich.net> wrote:
>>>>
>>>> On 2014-01-20 13:24, Wu, Feng wrote:
>>>>>>
>>>>>>
>>>>>> -----Original Message-----
>>>>>> From: xen-devel-bounces@lists.xen.org
>>>>>> [mailto:xen-devel-bounces@lists.xen.org] On Behalf Of Gordan Bobic
>>>>>> Sent: Monday, January 20, 2014 8:50 PM
>>>>>> To: xen-devel@lists.xen.org
>>>>>> Subject: Re: [Xen-devel] vga passthrough with qemu-xen (or qemu
>>>>>> upstream)
>>>>>>
>>>>>> On 2014-01-20 12:31, Shakeel Butt wrote:
>>>>>>> On Mon, Jan 20, 2014 at 4:09 AM, Stefano Stabellini
>>>>>>> <stefano.stabellini@eu.citrix.com> wrote:
>>>>>>>> On Mon, 20 Jan 2014, Wu, Feng wrote:
>>>>>>>>>> -----Original Message-----
>>>>>>>>>> From: xen-devel-bounces@lists.xen.org
>>>>>>>>>> [mailto:xen-devel-bounces@lists.xen.org] On Behalf Of Shakeel
>>>>>>>>>> Butt
>>>>>>>>>> Sent: Monday, January 20, 2014 1:48 PM
>>>>>>>>>> To: xen-devel@lists.xen.org
>>>>>>>>>> Subject: [Xen-devel] vga passthrough with qemu-xen (or qemu
>>>>>>>>>> upstream)
>>>>>>>>>>
>>>>>>>>>> Hi all,
>>>>>>>>>>
>>>>>>>>>> Is it possible to do vga passthrough on xen-unstable with
>>>>>>>>>> qemu-xen
>>>>>>>>>> as
>>>>>>>>>> device model? I tried but I am getting error 'gfx_passthru'
>>>>>>>>>> invalid
>>>>>>>>>> parameter for qemu-xen. I am able to do passthrough with qemu
>>>>>>>>>> traditional i.e. qemu-dm.
>>>>>>>>>
>>>>>>>>> As far as I know, only qemu-traditional supports vga pass-through
>>>>>>>>> right now.
>>>>>>>>
>>>>>>>> Right.
>>>>>>>> It is not possible to assign your primary VGA card to a VM with
>>>>>>>> qemu-xen. You should be able to assign your secondary VGA card
>>>>>>>> though.
>>>>>>>
>>>>>>> Let me understand this correctly. If I have two VGA cards then I can
>>>>>>> passthrough
>>>>>>> secondary VGA card (in Dom0) to HVM as its primary VGA card. Is this
>>>>>>> right and
>>>>>>> if yes how can I do it?
>>>>>>
>>>>>> Passing any VGA card as a primary-in-domU has always been problematic.
>>>>>
>>>>>
>>>>>
>>>>> I think passing VGA card as a primary-in-domU works well in
>>>>> Qemu-traditional, right?
>>>>
>>>>
>>>>
>>>> I never managed to get it working - it certainly isn't just a matter of
>>>> enabling the option. There is at least the matter of also side-loading
>>>> the VGA BIOS, and IIRC that was limited to 64KB in size, which rules
>>>> out all ATI and Nvidia GPUs of the past 2-3 generations.
>>>>
>>>> Having said that - I never found a particularly good use-case for
>>>> primary passthrough. Once the GPU driver loads it works just the
>>>> same for all intents and purposes.
>>>>
>>>
>>> I have successfully managed to passthrough VGA card as primary to DomU
>>> with qemu traditional. I am trying to do the same with upstream qemu
>>> because
>>>   I need some new features of the upstream qemu which are not available
>>> in qemu traditional.
>>>
>>> With qemu upstream I can passthrough as secondary VGA card to DomU
>>> and able to see it in device manager in DomU (Windows 7) but Windows
>>> couldn't use it and display some error that another card is being used as
>>> display. I want Windows to use the passthroughed vga card  as its display.
>>
>>
>> Disable the other (emulated) card in device manager and reboot
>> the domU. That should fix it.
>
> This is not working for me. I am disabling the device and even uninstalling the
> driver but on reboot Windows 7 install the driver for the emulated vga and
> make it primary vga.

Don't uninstall the driver, just disable the device. If you uninstall 
it, it will get re-detected. If you disable it, it should show up with a 
red cross next to it, and your secondary GPU will start working the way 
you want it to.