Comment 11 for bug 1428121

Ubuntu 17.04 with 4.10.0-21, libvirt 2.5.0, QEMU 2.8, and virt-manager 1.3.2.
Gigabyte EX58-UD3R Rev 1.6, ICH10 (00:1b.0) audio, x5675 (Westmere).
Nvidia GTX 275 for the host, GTX 1050 Ti for the VM.

Added to /etc/default/grub, updated grub, rebooted, and replaced the previous entry each time:
intel_iommu=igfx_off (Audio works, breaks IOMMU)

intel_iommu=on,igfx_off (Breaks audio)

intel_iommu=on,igfx_off snd_hda_intel.align_buffer_size=1 (Breaks audio)

intel_iommu=on iommu=pt (Breaks audio)

dmesg gives with intel_iommu=on:
DMAR: [DMA Read] Request device [00:1b.0] fault addr ffffb000 [fault reason 02] Present bit in context entry is clear

THE FIX:
Alex Williamson created a patch that was verified by Matthieu Speder
https://bugzilla.kernel.org/show_bug.cgi?id=76331
https://patchwork.kernel.org/patch/4505951/