Re: [Qemu-devel] VFIO-VGA Issue

[Maik Broemme]

Hi Alex,

> >  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?
>
> It's either a bug in vfio or the above configuration issue with the
> pcieport.  I'd appreciate if you could advise how you're configuring the
> group for use.  Thanks,

I would like to continue the discussion because I have exactly the same
issue now with kernel 3.9.2 and CONFIG_VFIO_PCI_VGA enabled. The used
qemu version is latest git from today. The configuration which works is
my old one without x-vga=on and with -M pc. The used VGA device (ATI
Radeon 7870) is the following:

02:00.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI 
Pitcairn [Radeon HD 7800]
02:00.1 Audio device: Advanced Micro Devices [AMD] nee ATI Cape Verde/Pitcairn 
HDMI Audio [Radeon HD 7700/7800 Series]

I've created already a fresh install of Windows 7 (x64) and the result is
the following:

1) machine: q35 / kvm: yes / vga: none   / x-vga: on  = qemu freeze
2) machine: q35 / kvm: no  / vga: none   / x-vga: on  = qemu freeze (with 
errors below)
3) machine: q35 / kvm: yes / vga: none   / x-vga: off = qemu runs with 100% CPU 
due to no VGA init (no picture)
4) machine: q35 / kvm: yes / vga: cirrus / x-vga: off = qemu runs with BOSD on 
loading atikmpag.sys
5) machine: pc  / kvm: yes / vga: cirrus / x-vga: off = qemu runs fine

Regarding 2) it results in 100 messages like the following on the console
which runs qemu:

qemu-system-x86_64: vfio_vga_read(,0x3c3, 1) failed: Interrupted system call
qemu-system-x86_64: vfio_vga_read(,0x3c3, 1) failed: Interrupted system call
qemu-system-x86_64: vfio_vga_read(,0x3c3, 1) failed: Interrupted system call

Also the kernel produces some debug messages:

[ 4353.280592] WARNING: at lib/list_debug.c:36 __list_add+0x9c/0xd0()
[ 4353.280595] Hardware name: GA-990FXA-UD3
[ 4353.280598] list_add double add: new=ffff8803c53ede08, 
prev=ffffffff81ca3d58, next=ffff8803c53ede08.
[ 4353.280600] Modules linked in: vhost_net macvtap macvlan tun arc4 md4 
nls_utf8 cifs dns_resolver fscache vfio_iommu_type1 vfio_pci vfio bridge stp 
llc ip6table_filter ip6_tables it87 hwmon_vid snd_hda_codec_hdmi nvidia(POF) 
snd_hda_codec_realtek acpi_cpufreq mperf kvm_amd snd_hda_intel kvm crc32_pclmul 
crc32c_intel snd_hda_codec snd_hwdep snd_seq ghash_clmulni_intel snd_seq_device 
snd_pcm microcode k10temp edac_core fam15h_power edac_mce_amd r8169 sp5100_tco 
mii i2c_piix4 snd_page_alloc snd_timer i2c_core snd soundcore firewire_ohci 
mxm_wmi firewire_core crc_itu_t wmi
[ 4353.280652] Pid: 9762, comm: qemu-system-x86 Tainted: PF       W  O 
3.9.2-200.fc18.x86_64 #1
[ 4353.280654] Call Trace:
[ 4353.280661]  [<ffffffff8105f105>] warn_slowpath_common+0x75/0xa0
[ 4353.280667]  [<ffffffff8105f1e6>] warn_slowpath_fmt+0x46/0x50
[ 4353.280673]  [<ffffffff81316c0c>] __list_add+0x9c/0xd0
[ 4353.280678]  [<ffffffff810838fc>] add_wait_queue+0x3c/0x60
[ 4353.280685]  [<ffffffff813f20ed>] vga_get+0xdd/0x190
[ 4353.280690]  [<ffffffff81093e10>] ? try_to_wake_up+0x2d0/0x2d0
[ 4353.280698]  [<ffffffffa015b625>] vfio_pci_vga_rw+0xb5/0x230 [vfio_pci]
[ 4353.280704]  [<ffffffff8109780f>] ? __dequeue_entity+0x2f/0x50
[ 4353.280711]  [<ffffffffa0159279>] vfio_pci_rw+0x39/0x80 [vfio_pci]
[ 4353.280717]  [<ffffffffa015930c>] vfio_pci_read+0x1c/0x20 [vfio_pci]
[ 4353.280723]  [<ffffffffa011a0e3>] vfio_device_fops_read+0x23/0x30 [vfio]
[ 4353.280729]  [<ffffffff8119fed9>] vfs_read+0xa9/0x180
[ 4353.280734]  [<ffffffff811a02da>] sys_pread64+0x9a/0xb0
[ 4353.280740]  [<ffffffff81669a59>] system_call_fastpath+0x16/0x1b
[ 4353.280744] ---[ end trace 76b9d690c5d28216 ]---

So the only configuration which works so far is the old VFIO one without
the new patches for VGA passthrough using the following command line:

qemu-system-x86 \
        -machine pc \
        -cpu host \
        -smp cores=4,threads=1,sockets=1 \
        -m 8192 \
        -enable-kvm \
        -nodefaults \
        -vga none \
        -drive file=/dev/vg1/vm1,id=drive0,if=none,cache=none,aio=threads \
        -drive file=/dev/vg2/vm1,id=drive1,if=none,cache=none,aio=threads \
        -device virtio-blk-pci,drive=drive0,ioeventfd=on \
        -device virtio-blk-pci,drive=drive1,ioeventfd=on \
        -device vfio-pci,host=02:00.0,multifunction=on \
        -device vfio-pci,host=02:00.1 \

--Maik