TRUNC_PAGE
#define ROUND_PAGE(x) TRUNC_PAGE((x) + (NBPG - 1))
va = TRUNC_PAGE(va);
pa = TRUNC_PAGE(c->c_physoff + addr);
va = (vaddr_t)TRUNC_PAGE(bsh);
#define ROUND_PAGE(x) TRUNC_PAGE((x) + (PAGE_SIZE - 1))