Comment # 1 on bug 1189762 from Dainius Masiliunas

After doing a bunch of trial and error with kernel parameters, it turns out
that the culprit is indeed iommu. Obviously the intel_iommu option doesn't work
because this is AMD, but the regular iommu option makes a difference. It boots
to graphical interface with iommu=off (but then the mouse doesn't work), and it
boots correctly (including the mouse) with iommu=soft. No other iommu options
(e.g. iommu=calgary) make any difference.