[vfio-users] IGD (HD4600) hardware acceleration is disabled in some cases on host

[Alex Williamson]

On Fri, Sep 18, 2015 at 10:36 AM, Alexander Betaev <betaev at gmail.com> wrote:

> Hello,
>
> I noticed very strange behavior of HD4600 as host GPU.
> I have the following configuration: two cards (ATI&nVIdia) are passed
> through to two guest VMs and IGD is used as host GPU. But in several
> cases X server wont start with hardware acceleration saying:
> [    21.629] (II) Found 2 VGA devices: arbiter wrapping enabled
> [    21.635] (II) SELinux: Disabled on system
> [    21.636] (II) AIGLX: Screen 0 is not DRI2 capable
> [    21.636] (EE) AIGLX: reverting to software rendering
> [    21.780] (II) AIGLX: Loaded and initialized swrast
> [    21.780] (II) GLX: Initialized DRISWRAST GL provider for screen 0
>
> The scenario:
> 1. System boots up and start GDM
> 2. The *first user* logs in and has software rendering
> 3. *Second user* switches session (without terminating X with software
> rendering) and new X server has hardware rendering
> 4. When *second user* logs out, GDM shows up in X with software
> rendering, but if a user logs in as *first user* and then switches
> user then GDM shows up in X with HW accelerated rendering. So the next
> session will be started with HW rendering
>
> The workaround is obvious, but not convenient if host is used by
> several users. Starting gnome-shell in Wayland also solves the issue,
> but Wayland is very unstable in distribution I use.
>
> System is Debian 8.0 (Jessie/Stable) .The versions of packages:
> * xserver-xorg-video-intel 2:2.99.917-2~bpo8+1
> * linux-image-amd64 4.1+67~bpo8+1
> * gdm3 3.14.1-7
> * xserver-xorg-core 2:1.16.4-1
>
> Please advise.
>

If you're using OVMF for the assigned GPU VMs, then add the option
disable_vga=1 to the vfio-pci module and make sure the other GPUs are bound
to vfio-pci before Xorg starts on the host.  This disables VGA region
access through vfio and opts-out the bound devices from VGA arbitration,
leaving only one participant on the host.  If you're using x-vga=on,
there's really nothing that can be done without some code changes in Xorg.
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