my_zero_pfn
return my_zero_pfn(0) << PAGE_SHIFT;
unsigned long pfn = my_zero_pfn(vaddr);
unsigned long zeropage_pfn = my_zero_pfn(0);
entry = pfn_pte(my_zero_pfn(addr), vma->vm_page_prot);
entry = pte_mkspecial(pfn_pte(my_zero_pfn(vmf->address),
newpte = pte_mkspecial(pfn_pte(my_zero_pfn(pvmw->address),
zero_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),
_dst_pte = pte_mkspecial(pfn_pte(my_zero_pfn(dst_addr),