PHYSTOP            30 kernel/kalloc.c   freerange(end, (void*)PHYSTOP);
PHYSTOP            51 kernel/kalloc.c   if(((uint64)pa % PGSIZE) != 0 || (char*)pa < end || (uint64)pa >= PHYSTOP)
PHYSTOP            40 kernel/vm.c      kvmmap(kpgtbl, (uint64)etext, (uint64)etext, PHYSTOP-(uint64)etext, PTE_R | PTE_W);