Provide functions for accessing the underlying L4 table for mapper types

[phil-opp]

This is useful for setting up the recursive page table mapping in the UEFI bootloader implementation. I also think that this method makes sense in general, e.g. for determining unused memory ranges for new mappings.

[josephlr]

This makes sense. Some qjestions (that don't impact approval).

• Should we have a common trait for this mapper types?
• Is there a way to get the physical address of the L4 table for these mappers, so that we can load CR4?

[phil-opp]

Thanks for the review!

• Should we have a common trait for this mapper types?

I thought about that too. Using the existing Mapper/MapperAllSizes traits does not seem fitting to me, but perhaps it makes sense to add a new trait for it (especially if we add more such methods).

• Is there a way to get the physical address of the L4 table for these mappers, so that we can load CR4?

Yes, there is. We could for example reuse the MapperAllSizes::translate method for that.