question about amd64 pagetable page allocation.

[Mark Tinguely]

On Tue, Apr 3, 2012 at 8:33 AM, vasanth rao naik sabavat
<vasanth.raonaik at gmail.com> wrote:
> Hi,
>
> I am trying to understand the page table page allocation for a process in
> FBSD6.1. I see that the page table pages are allocated by vm_page_alloc().
> I believe the virtual address for this allocated page can be derived by
> PHYS_TO_DMAP(VM_PAGE_TO_PHYS(m)), however when I compare this address with
> the virtual address accessed in pmap_remove_pages() they are not the same.
>
> The virtual address of a *PTE in pmap_remove_pages() is something like
> *0xffff800000643200
> *
> However, the virtual address of the page allocated by vm_page_alloc() is  *
> 0xffffff033c6a0000
>
> *I would also like to understand the importance of loc_PTmap, I believe the
> pmap_remove_pages() is derving the page table page addresses from loc_PTmap?
> (kgdb) p loc_PTmap
> Cannot access memory at address 0xffff800000000000
>
> How do we relate the loc_PTmap to the page table pages allocated by
> vm_page_alloc() in _pmap_allocpte().
>
> Thanks,
> Vasanth



The answer to your questions will be more obvious when you get an
understanding of the Recursive Page Tables.

--Mark Tinguely.