A few notes for anyone trying this...
* I recommend the q35 machine type and using the default config
file found in the docs directory. This means your command line
should include:
-M q35 -nodefconfig -readconfig /path/to/qemu.git/docs/q35-chipset.cfg
* You're likely passing through a graphics card that is attached
to the host system below a root port, so make it appear that way
to the guest too. If your graphics card has a graphics function
and audio function, assign them as:
-device vfio-pci,host=2:00.0,x-vga=on,multifunction=on,bus=ich9-pcie-port-1,addr=0.0 \
-device vfio-pci,host=2:00.1,bus=ich9-pcie-port-1,addr=0.1
The bus name comes from the q35-chipset.cfg above. If your
graphics doesn't include a separate audio device, drop the
second line and the multifunction option of the first (addr is
also optional at that point, 0.0 will be the default).
* If you follow both of the above, your VGA device is now below a
root port, but the version of seabios in qemu doesn't support
initializing VGA routing to that device. To fix, use upstream
seabios: git://git.seabios.org/seabios.git The default config
should work. Then add the following to your qemu commandline:
-L /path/to/seabios.git/out/ -L /path/to/qemu/bios/files/
(the latter is likely /usr/local/share/qemu/)
* You can use -nographic to prevent QEMU from trying to start SDL
or need a vnc parameter. You can also specify a -vnc option and
use the window for mouse input.
* Use -vga none. At this point I'm not really interested in
dual-headed VMs unless you're interested in working on it.
Having an emulated VGA means we're not really testing VGA
support through VFIO.
* Do no use the vfio-pci romfile option unless you need it (ie.
try w/o first). Option ROMs check an internal signature against
the hardware. If they don't match, it isn't run. If you
download a ROM from the internet, you may get nowhere. If you
do need a ROM, it's best to scrape it off the device you're
using. You can do this through the "rom" file in sysfs for the
device. "echo 1 > rom" to enable it, the read it as "cat rom
> /tmp/rom". To do this, it should be a secondary graphics
device and be untouched by host drivers. You may have better
luck booting from an install CD to get an environment where the
device is untouched for this.
* USB passthrough is handy for input and easier than figuring out
which ports are connected to which USB controllers for vfio-pci
assignment. Use lsusb to find the devices, note the bus and
device numbers, the use:
-device usb-host,hostbus=8,hostaddr=2
I think that's it. Feel free to reply with other best practices.
Thanks,
Alex
On Fri, 2013-05-03 at 16:56 -0600, Alex Williamson wrote:
> Hi folks,
>
> A number of people have been trying VFIO's VGA support, a few have even
> been successful. Resetting devices has been a problem and makes it
> very, very difficult to really use VGA assignment effectively. The code
> in the branches below attempts to address this. Discrete graphics
> devices are typically on their own bus, which we can reset so we
> theoretically get something pretty close to a power-on state for the GPU
> on each run (or after each guest reset). With this I'm able to get
> multiple runs on my HD7850 with no need to reset the host. Hopefully
> this will also cleanup after any host uses of the device so we can
> unload driver rather than blacklisting them.
>
> If you've been playing with VFIO and VGA, please give the branches below
> a shot and report successes and failures. Note that this new reset is
> only enable with the x-vga=on option, so should not do gratuitous bus
> resets for other devices. Thanks,
>
> Alex
>
> git://github.com/awilliam/linux-vfio.git vfio-vga-reset
> git://github.com/awilliam/qemu-vfio.git vfio-vga-reset
>
> PS - The above linux branch is v3.9 based which has a known kvm emulator
> bug. If you're on Intel and nothing happens, try:
>
> sudo modprobe -r kvm_intel
> sudo modprobe kvm_intel emulate_invalid_guest_state=0
>
> This is required to execute the VGA BIOS on my HD7850.
>
> If things still don't work, apply the following patch:
>
> --- a/hw/misc/vfio.c
> +++ b/hw/misc/vfio.c
> @@ -40,7 +40,7 @@
> #include "sysemu/kvm.h"
> #include "sysemu/sysemu.h"
>
> -/* #define DEBUG_VFIO */
> +#define DEBUG_VFIO
> #ifdef DEBUG_VFIO
> #define DPRINTF(fmt, ...) \
> do { fprintf(stderr, "vfio: " fmt, ## __VA_ARGS__); } while (0)
>
> And log the output (there will be lots).
>
> Also, AMD/ATI and Nvidia are the only devices expected to have a
> reasonable shot at working. I'm seeing reports of success on AMD/ATI HD
> 5xxx, 6xxx, and 7xxx, as well as Nvidia Geforce 7-series, 8-series, 4xx
> series, and 6xx series. Older cards from those vendors probably aren't
> very interesting to support (honestly I wouldn't care much about 7/8
> series Nvidia or HD5xxx AMD, except I happen to have some for testing -
> use emulated VGA if you don't care about performance).
>
> Intel IGD graphics has numerous issues since it's partially incorporated
> into the chipset. Please don't bother to report IGD is broken unless
> you're interested in fixing it.
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