Re: [Qemu-devel] VFIO VGA passthrough

[Alex Williamson <alex.williamson@redhat.com>]

On Wed, 2012-11-21 at 19:56 +0800, ching wrote:
> On 11/20/2012 11:27 PM, Alex Williamson wrote:
> >
> > Getting VGA to work in a guest is mostly black magic and luck at this
> > point.  The warning you're getting isn't preventing anything.  We use
> > device reset to try to clear the state of the hardware between runs.  If
> > it's not available we can potentially leak data through the device and
> > may see issues with reproducibility since we can't return the device to
> > a known state.
> >
> > The assigned VGA device should not be used for anything on the host,
> > which it seems like you've taken care of.  The host shouldn't even have
> > a blinking cursor on the display.
> >
> > It's been reported that "-cpu host" helps, but that's possibly very
> > similar to what you specify below.  When I tested secondary VGA with an
> > ATI card I used "-vga std" and I made the devices appear as
> > multifunction in the guest, ex:
> >
> > -device vfio-pci,host=1:00.0,multifunction=on,addr=4.0 \
> > -device vfio-pci,host=1:00.1,addr=4.1
> >
> > I also first booted without the AMD Catalyst driver installed.  The
> > assigned devices are unused, but the guest still boots.  Then installed
> > the Catalyst driver, after which rebooting causes the std VGA to go
> > blank after an initial startup screen and Windows uses the assigned
> > device exclusively.  Good luck, there's obviously still work to do in
> > this space.  Thanks,
> >
> > Alex
> >
> >
> >
> >
> 
> i am new in pci passthrough has a few more question:
> 
> 1. is your vga card a PCI Express card?

Yes

> 2. there is a pci bridge in the same iommu group, do i need to pass to the guest?
> 
>     00:01.0 PCI bridge: Intel Corporation Xeon E3-1200/2nd Generation Core Processor Family PCI Express Root Port (rev 09)

No, though it's possible that using the new Q35 chipset model and
matching the topology of the devices in the guest (ie. both below an
emulated root port) may help.

> 3. do i need to dump the vga bios and pass it to guest?

Typically not for ATI/AMD cards.  If you can read the "rom" file
in /sys/bus/pci/devices/xxx/rom (where xxx is your device, ex
0000:01:00.0) then dumping the rom likely won't help.  Thanks,

Alex