Re: [Qemu-devel] VFIO-VGA Issue

[deniv]

> On Wed, 2013-04-10 at 16:32 -0400, address@hidden wrote:
>> >> However, turning gfx_passthru off did
>> >> the trick. Win7 started loading with cirrus and switched to HD7750
>> >> halfway
>> >> through boot proccess. I didn't do any testing just let Windows
>> >> calculate
>> >> its score. The result was 7.4 and Aero was working.
>> >
>> > You should be able to do this with vfio too, use -vga cirrus and don't
>> > use the x-vga option on pci-assign.  The x-vga enables legacy VGA
>> > support for boot and primary console, as a secondary head normal PCI
>> > device assignment should be sufficient.
>> >
>> Oh, how I wish it was true! Trying to load with cirrus and vfio-pci
>> results in BSOD:
>> Attemp to reset the display driver and recover from timeout failed.
>
> Is this a fresh windows install?  Windows doesn't like change and will
> BSOD pretty easily when attaching graphics to an existing image.
>
>> Trying the old pci-assign with kvm results in non-working GFX. Windows
>> shows code 10 and sometimes code 43 for the card.
>
> What happens if you don't use a q35 machine?  Windows is very particular
> about the PCIe type of a device and will often show Code 10 if it
> doesn't have a type compatible with a root complex.  Alternatively you
> can use the q35 config in the docs directory with the -readconfig option
> and the bus= option on the pci-assign device to place the graphics
> behind a root port.
>

After many attempts I have VGA passthrough working. Each test has been
performed in a clean Win7 install with kvm enabled. Installation was done
with i440fx machine and changed to q35 after virtio drivers were
installed. I did that because there's no AHCI driver for q35 yet and win7
doesn't have drivers for lsi scsi.

1. q35/pc, vga=none, vfio-pci, x-vga=on. Nothing on the VM's screen, debug
output can be seen in the previous mails.
2. q35/pc, vga=cirrus, vfio-pci, x-vga=on. Screen corruption on host
(correction to the previous mails: corruption also happens even in kms
console). Nothing on the VM's screen.
3. q35/pc, vga=cirrus, vfio-pci, no x-vga. BSOD: Attempt to reset the
display driver and recover from timeout failed.
4. q35, vga=cirrus, pci-assign. Windows boots, the graphic card doesn't
start: Code 10.
5. pc, vga=cirrus, pci-assign. IT'S ALIVE! Ironically, this is the oldest
way to assign pci devices in kvm. Why I could make it work previously?
Silly me!

After some testing I can say that the card can tolerate guest restarts,
but it also can freeze the host in process. I got such a freeze (after a
clean shutdown) once in about 10 restarts. On the other hand, killing the
guest during a heavy 3d benchmark and starting the guest again was fine.
Also, the card fails to clock up after a reboot, which causes poor
performance in heavy loads. Thanks to Xen wiki I found that they "fix"
this by ejecting the graphic card from Windows' panel. Oh, and the last
thing, I once had code 43 after a guest reboot, but rebooting the guest
again fixed it.

All in all, I'm quite happy now. Just wish that host freeze I had won't
happen again. Is it a bug in qemu, the catalyst driver, or VT-d?
Hopefully, q35 and vfio-pci will work some day. I wonder why q35 +
pci-assign doesn't work, and what's the problem with q35/pc + vfio-pci (no
x-vga). If vfio-pci is the direct replacement for pci-assign it must be a
bug in vfio, huh?