Re: [Xen-users] VGA/PCI Passthrough of Secondary Graphics Adapter

[Casey DeLorme <cdelorme@xxxxxxxxx>]

1) If passing declaring the BDF is all that is needed to pass a VGA card, in the same respect as an PCI device, then there is no difference between PCI passthrough and VGA passthrough IF the VGA card being passed through is not in use by the dom0?

From the perspective of Dom0, but graphics (aka VGA) cards from what I have read need legacy code support for things like boot-time handling, making it more complex than say network cards, SATA cards, video capture cards, or other types.

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2) The card I wish to pass is the 5570, in the secondary PCIe slot. It is not being used by the dom0, and is subsequently hidden (xen-pciback.hide).

AFAIK slot number doesn't mean anything to your DomU, so once the device is passed there is no "primary slot" in the mix.

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3) Neither Radeon in my system supports FLR; however, many people use the Radeon with VGA passthrough somewhat routinely. I seem to be having immense trouble getting this to work? I have not gotten anything to display other than a black screen (which does show that something is happening). I just can't understand why?

I have used a Radeon HD 6870 successfully since August last year in both Windows 7 and Windows 8 virtual machines.

For me the lack of FLR creates problems during:

- Driver installation

- Driver Upgrades

- System Reboots

The lack of FLR, to my understanding, prevents the virtual machine from resetting the card state, leaving it initialized when switching or rebooting your DomU. ÂAs a result the card is activated multiple times, creating various issues with a range of problems.

During my tests, I broke down the steps logically to resolve the issues I had installing and updating drivers. ÂIn general, anytime I update or install AMD drivers I would reboot the entire physical machine to ensure the graphics card state was proper.

From my experiences this required a freshly installed Windows system, if you are working on a system you already attempted driver installation on and it failed (BSoD's or otherwise) uninstalling the failed drivers and trying again loops back to the same failures for mostly unknown reasons. ÂPresumable it has to do with the use of the .NET framework for installation, and leaving bits of data behind on failure, but I never confirmed the exact details.

For me, once the drivers are properly installed, rebooting the system still leaves the card in a pre-initialized state, which to avoid performance degradation I would manually reset the card using eject media from the lower right icon. ÂThis is not a perfect solution, and I do not rely on it when performing driver installation or updates.

Note that Windows 8 especially, but also Windows 7, will attempt to automatically install drivers which for me led to reboots that broke my attempted installation. ÂI had to tell the system not to automatically update to work around this during the first installation process.

Again, this is my experience, other users have reported vastly different problems with a range of other possible causes and many unsolved.

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And regarding the BSODs, when I install the card, I've gotten it to say "Functioning normally" in Device Manager, but the screen is disabled in "Screen Resolution," and the when I attempt to "Extend to Display" in order to enable the Radeon monitor, the screen goes blank and the system crashes. Upon reboot, the system BSODs (atikmpag.sys) I've tried physically powering down dom0 and bringing it back up, but the error persists.Â

As an aside, I've compiled Xen with a patch that supposedly fixes these issues (patches qemu-dm), and I've attempted to use the script provided (run-passthrough), but that hasn't resulted in any change whatsoever.

Since we haven't verified this yet, are you using Xen 4.2 and the xl toolstack?

Also, how are you checking the Device Manager? ÂIf you are still using SDL or VNC then you are using the emulated graphics, and you cannot extend emulated to physical, you either use one or the other. ÂTry changing the monitor source to use the AMD input, and reboot the system after the drivers are installed and it should automatically begin sending video to your monitor. ÂTo get mouse and keyboard to the system pass a USB controller and use new inputs. ÂTechnically you can still send input through VNC, but that may not work well.

The reboot error is consistent with my diagnosis above, you can try my suggestions but I can by no means claim they will work for you. ÂIf you applied the AMD primary patch to Xen source before building, have you added the passthrough flag to your DomU configuration and seeing if that changes anything.

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