Charlie Jacobsen authored Jun 25, 2014 and Vikram Narayanan committed Oct 25, 2016

This was tricky. Unfortunately, since guest physical
addresses are wrapped in the paging entries, we can't
use some of the linux macros / routines (e.g.,
pud_offset). This would allow us to benefit from pud-
and pmd-folding, making the code more portable. Perhaps
we'll think of something later...

The code will only work on a linux with 4 paging levels
(pgd, pud, pmd, page table). lcd_mm_gva_walk is the
main routine that traverses the hierarchy. Each subroutine
translates a paging structures guest physical to host
virtual address, and gets the correct entry.

A simple watermark is used (rather than a bitmap) for
allocating guest physical memory.