Hi,
I think i might have solve it.
For some reason grub2-mkconfig doesnt work. (Have no idea why)
Is this on CentOS 7?
Well, yes, I remember that it didn't work for me when I installed new servers one or two years ago, that was with CentOS 7 and they were my first EFI installs.
I manage to solve it with grubby.
sudo grubby --args="intel_iommu=on" --update-kernel=ALL
For some reason it works. I dont know if it works if my kernel gets upgraded.
I have restored the original configs after messing with grub2-mkconfig and only used kernel installs to further modify grub config. That way it has always worked for me. And I was a bis scared by the whole EFI, grub2 and everything around it because I felt I don't really understand how it all interacts in detail.
Regards, Simon