Am 15.08.2017 05:26, schrieb taii...@gmx.com:
On 08/14/2017 11:16 PM, Alex Williamson wrote:

On Mon, Aug 14, 2017 at 9:07 PM, taii...@gmx.com <taii...@gmx.com> wrote:

I am not sure but I think there are no pci-e audio cards that support
IOMMU AFAIK.

False, especially for device assignment, the drivers in the guest and the
guest itself is completely unaware of the IOMMU.
I heard an Asus Xonar (cmedia chipset) PCI-e (all of them are based
off that chip AFAIK) wouldn't work and resulted in IO_PAGE_FAULT dmesg
spam with iommu enabled.
https://bbs.archlinux.org/viewtopic.php?id=168555


The statement is definitely false. I'm currently passing the built-in PCIe Intel HDA of my X99 motherboard to the VM. The HDA is nicely isolated in its own IOMMU group and the VM controls it flawlessly. Furthermore, libvirt does automatic unbind/rebind with the host driver upon booting up and shutting down the VM. PulseAudio plays nicely along and automatically reroutes all active streams to the other sound device on the host, which happens to be...

an Asus Xonar STX II. When it comes to Xonars, those use a PCI chip with an
on-card PCIe-to-PCI bridge:

07:00.0 PCI bridge [0604]: ASMedia Technology Inc. ASM1083/1085 PCIe to PCI Bridge [1b21:1080] (rev 04) (prog-if 00 [Normal decode])
        Flags: bus master, fast devsel, latency 0, IRQ 18, NUMA node 0
        Bus: primary=07, secondary=08, subordinate=08, sec-latency=32
        I/O behind bridge: 0000c000-0000cfff [size=4K]
        Memory behind bridge: None
        Prefetchable memory behind bridge: None
        Capabilities: [50] MSI: Enable- Count=1/1 Maskable- 64bit+
        Capabilities: [78] Power Management version 3
Capabilities: [80] Express PCI-Express to PCI/PCI-X Bridge, MSI 00
        Capabilities: [c0] Subsystem: Device [0000:0000]
        Capabilities: [100] Virtual Channel
        Kernel modules: shpchp

08:04.0 Multimedia audio controller [0401]: C-Media Electronics Inc CMI8788 [Oxygen HD Audio] [13f6:8788] Subsystem: ASUSTeK Computer Inc. Virtuoso 100 (Xonar Essence STX II) [1043:85f4] Flags: bus master, medium devsel, latency 32, IRQ 18, NUMA node 0
        I/O ports at c000 [size=256]
        Capabilities: [c0] Power Management version 2
        Kernel driver in use: snd_virtuoso
        Kernel modules: snd_virtuoso

Works with iommu=pt, though I believe it also worked without it (I'm not
really sure why I added the iommu parameter). I still haven't tried passing the Xonar to the VM. The two devices appear to be grouped together with the
PCH PCI bridge. I'll try in the future.

I had a similar error - one of my GFX cards broke so I slotted in an
old PCI-e Nvidia 7800gt and when booting dom0 and trying to do
modesetting with IOMMU enabled it would spew io page faults and fail
to modeset - I had to replace it with a newer card...I do not know why
that occurred.

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