PGROUNDDOWN       351 kernel/vm.c        va0 = PGROUNDDOWN(dstva);
PGROUNDDOWN       388 kernel/vm.c        va0 = PGROUNDDOWN(srcva);
PGROUNDDOWN       419 kernel/vm.c        va0 = PGROUNDDOWN(srcva);
PGROUNDDOWN       465 kernel/vm.c      va = PGROUNDDOWN(va);