rem: put_pgtable_in_pgdir(pdentry *e, addr_t pgtable_phys, int attributes)
add: put_pgtable_in_pgdir(pdentry *e, addr_t pgtable_phys, uint32 attributes)
context: put_pgtable_in_pgdir(pdentry *e, addr_t pgtable_phys, int attributes){	// put it in the pgdir	init_pdentry(e);	e->addr = ADDR_SHIFT(pgtable_phys);	// if the region is user accessible, it's automatically read/write	// accessible in kernel space	e->user = (attributes & B_USER_PROTECTION) != 0;	if (e->user)		e->rw = (attributes & B_WRITE_AREA) != 0;	else		e->rw = (attributes & B_KERNEL_WRITE_AREA) != 0;	e->present = 1;}