[Xen-users] Problems with VGA Passthrough

[Paolo Cancedda <paolo.cancedda@xxxxxxxxx>]

Hi all,

I'm trying, without success, to get VGA Passthrough working.

My relevant hardware configuration is:

- Intel i7-3770 (supports VT-d)

- ASRock Z77 Pro4-M (VT-x and VT-d enabled from BIOS)

- AMD Radeon HD7750, enumerated as 01:00.0 (VGA) and 01:00.1 (HD audio)

- AMD Radeon HD6450, enumerated as 02:00.0 and 02:00.1 (I physically removed this one on my latest tests) 

On dom0 I run an Ubuntu Server 12.04.2 LTS 64 bit, kernel version 3.5.0-34.55~precise1, xm tools.

I have a Windows 7 32 bit virtual machine that works regularly with gfx_passthru=0

I blacklisted modules radeon and snd_hda_intel.

At boot, console is on HD7750, then it switches to onboard Intel HD Graphics, leaving the HD7750 screen black and on.

In /etc/rc.local I call a script to bind pciback driver to 01:00.0, 01:00.1, 02:00.0, and 02:00.1

My tests were mainly with HD7750, but I gave some tries also to HD6450

I used:

- Ubuntu supplied Xen 4.1.2-2ubuntu2.10

- Xen 4.2.2 built from sources

- Xen 4.3-unstable from git HEAD

The results:

- Xen 4.1.2-2ubuntu2.10

  - with gfx_passthru=1 and pci=['01:00.0'] xm create apparently works but the screen remains off (to be precise, it goes DPMS off on the first run after a reboot and stays off for the followings)

  - with gfx_passthru=0 and pci=['01:00.0','01:00.1'] xm create fails with "Error: (22, 'Invalid argument')" (but the screen goes off on the first try after a reboot)

- Xen 4.2.2

Build:

  - git clone git://xenbits.xen.org/xen.git xen-devel

  - git branch pac-4.2.2 RELEASE-4.2.2

  - git checkout pac-4.2.2

  - ./configure --prefix=/usr/local

  - make -j9 world

  Install:

  - sudo make -j9 install

  - replacement of /etc/init.d/xen* with modified ones in order to make everything start on Ubuntu

  - ldconfig

  - reboot

Results:

  - with gfx_passthru=0 and pci=['01:00.0','01:00.1'] xm create fails with "Error: (22, 'Invalid argument')" (but the screen goes off on the first try after a reboot)

  - with gfx_passthru=0 and pci=['01:00.0'] xm create works

  - with gfx_passthru=1 and pci=['01:00.0'] xm create starts the virtual machine but the screen remains off, VM CPU stays high (~70%) until xm shutdown; if I start again the VM with gfx_passthru=0, it starts and Windows does not complain about being shut down uncleanly (I think that with gfx_passthru=1 guest OS does not even start bootstrapping)

- Xen 4.3-unstable

Build:

  - git checkout master

  - git clean -f -d -x

  - git reset --hard

  - git branch pac-4.3-unstable 

  - git checkout pac-4.3-unstable

  - ./configure

  - make -j9 world

Install:

  - sudo make -j9 install

  - replacement of /etc/init.d/xen* with modified ones in order to make everything start on Ubuntu

  - ldconfig

  - reboot

Results:

  - with gfx_passthru=0 and without pci=... xm create works, VM starts and works, screen stays black & on

  - with gfx_passthru=0 and pci=['01:00.0','01:00.1'] xm create works, VM starts and works, screen goes off

  - with gfx_passthru=1 and pci=['01:00.0','01:00.1'] xm create starts VM, screen goes off, VM CPU goes 70% and stays there; VM does not boot; last message I see with xm dmesg is ROMBIOS Revision "$Revision: 1.221 $ $Date: 2008/12/07 17:32:29 $"

I investigated  4.3-unstable. Adding logs to tools/firmware/rombios/rombios.c, I discovered that VM gets stuck in call to VGA ROM init.

I also gave a look to the 'Invalid argument' failure in 4.2.2

Call to pirq_permit_access() on IRQ 17, the interrupt of HD audio at 01.00.1 , returns -EINVAL

The failing call chain is:

  do_domctl(cmd=XEN_DOMCTL_irq_permission, allow=1, pirq=17) ->

  pirq_permit_access() ->

  domain_pirq_to_irq() ->

  pirq_field() ->

  pirq_info() ->

  radix_tree_lookup()

radix_tree_lookup() fails to find the structure for IRQ 17, while it succeeds finding IRQ 16, belonging to VGA at 01.00.0

I tried also secondary passthrough, but the native driver installation program crashes and shortly afterwards Windows guest goes blue screen.

Here is my VM configuration:

builder='hvm'

memory = 1024

vcpus=1

name = "win7"

vif = ['bridge=xenbr0']

disk = ['phy:/dev/xen2/win7,hda,w']

acpi = 1

device_model_version = "qemu-xen-traditional"

device_model = 'qemu-dm'

stdvga=1

usbdevice='tablet'

boot="c"

sdl=0

serial='pty'

vnc=1

vnclisten="0.0.0.0"

vncpasswd=""

vncdisplay="7"

xen_platform_pci=1

viridian=1

apic=1

gfx_passthru=1

pci=['01:00.0','01:00.1']

I can provide all the configuration files and logs you desire.

I can also try patches, other Xen versions and, if needed, another kernel (even building it from sources), but I fear I'm missing some very basic detail :-/

What are your advices?

Cheers,

Paolo

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