rem: put_ptentry_in_pgtable(ptentry *e, addr_t pgtable_phys, int attributes)
add: put_ptentry_in_pgtable(ptentry *e, addr_t pgtable_phys, uint32 attributes)
context: put_ptentry_in_pgtable(ptentry *e, addr_t pgtable_phys, int attributes){	// put it in the pgtable	init_ptentry(e);	e->addr = ADDR_SHIFT(pgtable_phys);	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;}