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Date: Thu, 23 Jan 2014 11:37:02 +0200
From: laine@laine.org
To: thepowertool_sc@hotmail.com
Subject: Re: [libvirt-users] PCI Passthrough

Laine,

Thank you very much for your response.

I took a look at the first link you provide (archlinux).  Key items that caught my attention (in order):

1.  "Intel IGDs won't work"--I have Intel integrated video
2.  "NOTE:  THIS IS EXPERIMENTAL SO IT MIGHT NOT WORK FOR YOU" (self-explanatory)

One additional note:  When I received the "permission denied" error I had the same thought as you.  I was unaware of the issue you outlined with libvirt needing to be configured to run as root on some versions of Fedora.  Still, as root I did successfully detach my video card... at least that's how it appeared given the monitor went no-signal and then displayed a strange pattern.  The system wouldn't ping and failed to respond to ssh attempts.  I had to reboot to recover.  I tried a second experiment where I first started a ssh session and then detached (from the host).  Going back to the 2nd system the ssh session stopped responding.

Actually that's probably more of an indication that your kernel just doesn't properly handle having the primary video device disappear midstream. You may have different results if you connected two video cards to a system, and tried to passthrough the secondary (it still probably wouldn't work, but it would likely fail in a different way).

That leads me to believe it's not fully baked, something critically fails, and it's not going to work for me at-least at my current levels.

Alex Williamson gave a talk at this year's KVM Forum (in October) about the difficulties of making VGA passthrough work, and it was truly frightening; there are just too many strange, undocumented backdoors in the devices that are required by the drivers for proper operation.

In my mind this whole area just has too great of a likelihood of total failure without possibility of making it work in a reasonable time frame.

To answer your question:  I'm running Fedora 18.

F18 was definitely one of the releases that was broken wrt PCI passthrough requiring qemu to be run as root. I don't recall if the kernel guys ever fixed it in that version or not. I pestered them about it for months, then finally gave up.

BTW, you know that F18 has just gone end-of-life, right? This means no more updates of any type, even security updates. You can actually upgrade your F18 machine to F19, and F19 to F20, using the "fedup" package (I haven't tried using fedup to go directly from F18 to F20, but I suppose you could look into it). *A lot* has changed in virtualization in the last year, and as a bonus, you'll be covered for security fixes for another year.

Is there a place where I can follow updates and see PCI pass-through mature so I'll know when next to try?

Well, you could try the qemu-devel mailing list, but it's pretty high traffic, and very few of the messages would be on this particular topic. That *is* the place where any discussion would take place, though.

Thank you, again, for your help!

BTW, it's best to keep all messages on the list rather than private replies. That way someone else with better information may reply (and people very often get busy and disappear for several days/weeks at a time, so it's better to not rely on a response from a single person)