Re: PCI Passthrough

The PowerTool <thepowertool_sc@xxxxxxxxxxx> · Thu, 23 Jan 2014 10:07:33 -0500

Oops!  I blame Microsoft.  I use Hotmail and am very, very unhappy that MS bought them out which leaves me stuck with Outlook, which sucks.  I've always just hit reply in the past and it's worked.  Now I'm going to have to be careful to make sure my replies go where I expect them.

Thank you very much for the information.  I was really hoping to consolidate systems but that apparently won't happen in the near future.  So that means I'll be focusing my efforts on getting my Spacewalk server updated and then upgrading from F18 to F20 or 21.  Yep, I was very aware of F18 dropping and thankful for the one brief delay.

I'll be taking a look at it again once I upgrade to the current Fedora.  If that doesn't work I'll wait and keep an eye on posts and when things look better probably get new hardware (which will likely be the requirement).

Thanks, again!

Date: Thu, 23 Jan 2014 11:37:02 +0200
From: laine@xxxxxxxxx
To: thepowertool_sc@xxxxxxxxxxx
Subject: Re:  PCI Passthrough

    On 01/21/2014 05:32 PM, The PowerTool
      wrote:

      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)

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