This example was done on Ubuntu server.
* Enable VM direct I/O in the BIOS.
/etc/default/grub using an editor like nano or something.
GRUB_CMDLINE_LINUX_DEFAULT and add
intel_iommu=on as a parameter. Make sure it's lowercase. Save and exit.
shutdown -r now
dmesg | grep -e DMAR -e IOMMU and you should see a line in there stating that IOMMU is enabled.