linux内核执行fork时对写时复制的设置

sys_fork
  -> kernel_clone
    -> copy_process
      -> copy_mm
        -> dup_mm
          -> dup_mmap
            -> copy_page_range
              -> copy_p4d_range
                -> 如果时PUD巨型页：copy_huge_pud: 分别将父子的PUD页表项设置为写保护
                  -> pudp_set_wrprotect(src_mm, addr, src_pud);
                  -> set_pud_at(dst_mm, addr, dst_pud, pud_mkold(pud_wrprotect(pud)));
                -> copy_pmd_range
                  -> 如果是PMD巨型页：copy_huge_pmd: 分别将父子的PMD页表项设置为写保护
                    -> pmdp_set_wrprotect(src_mm, addr, src_pmd);
                    -> set_pmd_at(dst_mm, addr, dst_pmd, pmd_mkold(pmd_wrprotect(pmd)));
                  -> copy_pte_range
                    -> copy_present_pte
                      -> 如果：is_cow_mapping(vm_flags) && pte_write(pte)
                        -> ptep_set_wrprotect(src_mm, addr, src_pte);
                        -> set_pte_at(dst_vma->vm_mm, addr, dst_pte, pte_wrprotect(pte));