Maybe related: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1413440.
When I use the workaround described in comment 29 in bug 1413440 (booting with GRUB options 'pci=nomsi iommu=soft') then XHCI doesn't hang, and when I run the reset script described in this bug report, it doesn't cause a kernel bug.
Maybe related: https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1413440.
When I use the workaround described in comment 29 in bug 1413440 (booting with GRUB options 'pci=nomsi iommu=soft') then XHCI doesn't hang, and when I run the reset script described in this bug report, it doesn't cause a kernel bug.