PGD_MASKED_BITS   999 arch/powerpc/include/asm/book3s/64/pgtable.h #define pgd_page_vaddr(pgd)	__va(pgd_val(pgd) & ~PGD_MASKED_BITS)
PGD_MASKED_BITS    59 arch/powerpc/include/asm/nohash/64/pgtable-4k.h #define pgd_page_vaddr(pgd)	(pgd_val(pgd) & ~PGD_MASKED_BITS)