Re: Xen 4.0.0 first release candidate / graphics passthru

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

Timothy J. Moore wrote:
> Hang-on guys there is already basic GFX passthru functionality since XEN 3.4 (Weidong Han provided patches).
>
> changeset 20144: http://xenbits.xensource.com/xen-unstable.hg?rev/05f3ca68f62d
>
> You need to enable "gfx_passthru=1" in XEN config and set the pci=['<yourgfxcardid>'] also.
>
> The patches allow passthrough of the Primary VGA card only and will re-execute the VGA BIOS within qemu (not the emulated Cirrus/Bochs BIOS).
>
> This does seem to work for basic cards, ie Intel and some ATI but not NVIDIA Cards as they still need the pBAR=vBAR patches.
>
> I have been monitoring XEN_devel for a long time and have just tried the latest 4.0-rc2 (and manually hacked the pBAR=vBAR code in) without success .. maybe something else has changed to stop this working ?
>
> Weidong Han also provided patches to allow Secondary VGA passthru which Teo En Ming was able to reproduce. It is a subset of these patches that are in XEN now but only for the Primary card and I have not seen much testing of this functionality on the xen-devel list.
>
> Further development is needed but the main blocker to this whole VGA passthrough argument is support for FLR. In each of the above cases it seems that a reboot is needed to restore the VGA after stopping the associated DomU.
>
> PCIe FLR (Function Level Reset) is in the PCIe 2.0 specification, XCI (xenclient) does try to implement secondary bus resets to work around this - but it all seems to be very vendor_specific and I have never seen my VGA card reset and become re-usable.
>
> How would it work with PCI or AGP cards - if at all ?
>   
FLR is a requirement of device assignment to make sure the device is in 
a correct status. gfx passthrough also need to do FLR on gfx card for 
each assignment. XCI implements vendor specific FLR for some gfx cards 
(e.g. Intel IGD) if they don't support standard PCIe or PCI FLR. As I 
said before, many gfx cards are not virtualization friendly due to 
various issues, such as BIOS re-execution, FLR capability, pBAR=vBAR 
etc. First, let's implement a gfx passthrough framework in Xen to 
support vritualization friendly gfx cards, and then improve it to work 
with more gfx cards with clean hacks. At the same time, hope gfx vendors 
to improve their gfx cards to be more virtualization friendly in future.

Regards,
Weidong


> Hope this helps set the scene and current status,m anyone have anything else to add ?
>
> Cheers,
> Tim
>
>
> -----Original Message-----
> From: xen-devel-bounces@lists.xensource.com [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Pasi Kärkkäinen
> Sent: 21 January 2010 14:24
> To: Keir Fraser
> Cc: Sander Eikelenboom; xen-devel@lists.xensource.com; Weidong Han; Mr. Teo En Ming (Zhang Enming); Jean Guyader
> Subject: Re: [Xen-devel] Xen 4.0.0 first release candidate / graphics passthru
>
> On Thu, Jan 21, 2010 at 04:11:52PM +0200, Pasi Kärkkäinen wrote:
>   
>> On Thu, Jan 21, 2010 at 02:02:10PM +0000, Keir Fraser wrote:
>>     
>>> On 21/01/2010 13:03, "Weidong Han" <weidong.han@intel.com> wrote:
>>>
>>>       
>>>>>> We will rebase the patchset for both 2.6.18 and pvops dom0, and resend
>>>>>> if for check in after xen 4.0.
>>>>>>      
>>>>>>             
>>>>> Is there some specific reason to not have it in now, for Xen 4.0?
>>>>>   
>>>>>           
>>>> It needs some efforts to  rebase it to latest Xen. If you don't think
>>>> it's too late for Xen 4.0, we can try to complete it in a few days.
>>>>         
>>> If there is demand, then we can slip rc2 some more for it.
>>>
>>>       
>> I think the patches should go in for rc2. Already today multiple people have 
>> been asking how to run VGA passthrough with Xen :) (on #xen)
>>
>>     
>
> .. and in general it's a pretty popular question on both xen-users mailinglist and on #xen.
> People seem to want to use Xen VGA passthrough.
>
> -- Pasi
>
>
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