intel_iommu=on, but no iommu_groups

I know this is late, but to check that VT-d is enabled can be tricky depending on the UEFI Bios that you are using. For my Asus X99A USB 3.1 Motherboard, the settings for VT-x and VT-d are in different locations.

For VT-d: Advanced => System Agent Configuration => Intel VT for Directed I/O (VT-d)

On my system this was set to Disabled, even though VT-x (under Advanced => CPU Configuration => Intel Virtualization Technology) was enabled.

Make sure that both are enabled

I have met the same problem, and I check my BIOS setting and found out that VT-d had been disabled. I enabled the option and solved the problem. Maybe you could look up your motherboard or chipset manual to find if your machine support intel vt-d.