Question:
I was wondering if it's actually possible to put all the memory management of an OS into the user space?

Thoughts:
I suppose that all traps must go through the kernel, but nothing would stop the kernel from calling up to user space, right?
The question popped up in my head when reading about a user-mode paging system which, according to the book, wouldn't have access to the R and M (referenced and modified). But I can't quite grasp the why of it.
I mean, sure, if the paging table is in the kernel space, then it wouldn't be able to access it, but if it were in user space, there would be no problems. And as far as I know, there is no hardware that can keep track of all the R and M bits of all pages.

Discussions are welcome!
Operating systems are fascinating.