Re: [Qemu-devel] VFIO-VGA Issue

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

On Tue, 2013-04-09 at 08:22 -0400, deniv@lavabit.com wrote:
> Hi!
> 
> I've tried passing through my ASUS Radeon HD7750, but qemu just hogs 100%
> of one core and stops. Since the display didn't light up, I couldn't see
> how far Win 7 boot went. For a Linux guest I tried redirecting kernel
> messages to serial console, but there was nothing (qemu stops even before
> kernel start?).
> 
> Also, this GPU is kinda troublesome: it doesn't work with the proprietary
> driver if VT-d is enabled in BIOS (boot process stops with "dmar: DRHD:
> handling fault status reg 3"). The GPU works with the FOSS driver, though.
> Could this somehow be related to the passthrough issue?
> 
> Anyway, VT-d in pci-assign mode works for network adapters on this host.
> It runs kernel 3.9.0-rc5 (with vfio-vga enabled), qemu git from yesterday,
> and seabios 1.7.2. The host has no driver installed for the GPU. Before
> assiging it to qemu I'd run "echo '1002 683f' >
> /sys/bus/pci/drivers/vfio-pci/new_id" and the same for the associated HDMI
> device. Command line:
> qemu-kvm -machine q35,accel=kvm \
> 	 -cpu host -smp 4 -m 2G \
> 	 -vga none -display none \
> 	 -kernel /kvm/kernel-3.7.8 -append 'root=/dev/vda console=ttyS0' \
> 	 -drive
> index=0,media=disk,cache=none,if=virtio,aio=native,file=/dev/vg3/gpu \
> 	 -device vfio-pci,host=01:00.0,x-vga=on \
> 	 -device vfio-pci,host=01:00.1 \
> 	 -serial telnet:127.0.0.1:52990,server

You should always at least get monitor sync if it's going to work, but
you may have to reboot the host between each attempt.  I've been doing
most of the VGA development on an AMD box and swapping over to an Intel
system reminds me why.  Try removing the ",accel=kvm -cpu host -smp 4"
pieces of your command an try again.  If that works, it means there are
still broken bits of real mode handling in KVM.  My HD7850 hangs on an
Intel host the same way you describe, but posts if I disable KVM
support.  Thanks,

Alex