adding entries to swapper_pg_dir after boot

Hi, I am trying to address a range of special addresses in the kernel that are not visible(addressable) to memory at boot time. I create a whole in the virtual address space and then I want to try to add page table entries to the kernel page table for these VA<->MY(PA) translation. (Let me know if there is a better way to do this) I was wondering if anyone knew how do I go about this. I can access the kernel page tables from swapper_pg_dir. How do I add pgd enteries for these virtual addresses? Any sample code/reference will be helpful. Thanks, Asim