Re: [Xen-users] Problems with VGA Passthrough

[Gordan Bobic <gordan@xxxxxxxxxx>]

On 07/08/2013 05:20 PM, Paolo Cancedda wrote:
> Hello Javier,
>
> On Wed, Jul 3, 2013 at 10:56 PM, dkeruza <dkeruza@xxxxxxxxx
> <mailto:dkeruza@xxxxxxxxx>> wrote:
>
>
>     I ended up compiling xen 4.1.4 with patches for VGA Passthrough
>     [...]
>     Check this message for info.
>     
> http://xen.1045712.n5.nabble.com/VGA-passthrough-radeon-4850-as-primary-card-tp5714485p5714606.html
>
>
> following your advice, I was able to see VGA Passthrough working for the
> very first time.
> I compiled Xen 4.1.4 after applying the patches here:
> ftp://ftp.enjellic.com/pub/xen/xen-4.1.3.ati-passthrough.patch
> The installation was a bit messy, since makefiles of 4.1.4 did not honor
> PREFIX variable.
> USB passthrough does not seem to work, I used PCI passthrough of one of
> the two EHCI controllers on the motherboard.
> Unfortunately, however, with this setup my VMs are quite unstable.
> A Windows 8 VM reboots after waiting for some time after boot, before
> logging in.
> A Windows 7 VM at first seemed to work, but it stopped responding after
> being left alone for a few minutes (perhaps it's something related to
> power management).
> Do you know why these patches are not on Xen development tree (yet)?
> Cheers,
I have it all working stably with 4.2.2 with only the XSA patches (using 
RPMs from the CRC repository). I am also using PCI passthrough for a USB 
controller (I have two USB ports on the same physical controller, which 
is handy as I only have to pass in one USB controller).
If you are using > 2GB of RAM in domU this is going to cause you the 
sort of instability that will drive you nuts - it certainly did for me, 
and the only reason I persevered in the face of extreme frustration is 
because KVM didn't work for me with VGA passthrough _at all_, and ESX 
was a non-starter due to my hardware's lack of ACS capable PCI bridges 
which according to documentation, ESX needs for PCI passthrough. DomUs 
with > 2GB of RAM are not going to work with passing through devices 
with large BARs such as GPUs. A fix for this bug is in 4.3, due out any 
day now.
I had mixed luck with ATI passthrough, I'm using quasi-Quadro cards 
(GeForce modified into Quadro, see here for some details:
http://www.altechnative.net/2013/06/23/nvidia-cards-geforce-quadro-and-geforce-modified-into-a-quadro-for-virtualized-gaming/

Since the article I've moved further with the quasi-Quadros, I currently 
have a GTX470 (Quadro 5000) and a GTX480 (Quadro 6000) passed through to 
two separate VMs, and this is working lovely. No performance 
degradations or host crashes with domU reboots any more. As far as I can 
tell, judging by what ended up in dom0 syslog, the crashes were caused 
by PCI memory overwrites (AER errors all over the logs, search the 
archives for my previous reports on the subject). I am not sure why the 
host crashes have actually stopped when rebooting VMs, but when I got 
the 2nd VGA passthrough domU set up, the problem just went away. All in 
all, I'm finding quasi-Quadros just work a lot better than ATIs in terms 
of how they handle domU restarts and re-initialization.
I'm currently using an 8800GT card for dom0, but am hoping to switch to 
an ATI 4850, purely so that I can make my life easier by blacklisting 
all the nvidia drivers and not having the complication of selective 
pre-emptive partial detaching of Nvidia devices before the nvidia driver 
loads. Unfortunately, cards later than ATI 4xxx are unusable for me due 
to only having one DL-DVI capable port (one of the insurmountable 
reasons why Nvidia is the only option for me at the moment).
Gordan

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