Removing CR3 check from RecursivePageTable?

This issue is mostly for discussion purposes, to clarify my understanding.

RecursivePageTable::new() requires the passed page table to be active, checked through CR3. However, I'm not entirely sure I grok why that is. Nothing else in RecursivePageTable references CR3 in any way, other than that one particular check.

The reason I'm looking to remove this, is because I'd like to be able to have my kernel map in new page tables, for processes/drivers/etc, by mapping in the new page table at some address within the kernel space, and calling that "recursive" - the algorithms would all be the same, it would simply be a different P4 being referenced. In this way, I don't need to have every page table mapped into the kernel constantly for no reason, I don't need to manually manage pages when there's a perfectly good implementation already written, and generally it would simplify the setup.

However, I don't consider myself familiar enough with the implementation to know why the CR3 check is in place, and whether or not it is safe to remove. Could somebody with this knowledge advise please?

Start by reading the implementation of RecursivePageTable::new() and the CR3 check it performs. Trace how RecursivePageTable uses the selected page table and determine whether supporting a non-active page table is safe. Done means reaching and documenting a clear decision about removing or retaining the check; the issue does not name specific files or tests.