Hi Peter,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v5.14-rc1 next-20210714]
[cannot apply to hnaz-linux-mm/master asm-generic/master linux/master]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20210715-062718
base:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 8096acd7442e613fad0354fc8dfdb2003cceea0b
config: x86_64-randconfig-r021-20210714 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 0e49c54a8cbd3e779e5526a5888c683c01cc3c50)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://github.com/0day-ci/linux/commit/8b3e70f40b8333a803e642ed5c8cce738985881c
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20210715-062718
        git checkout 8b3e70f40b8333a803e642ed5c8cce738985881c
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> mm/memory.c:4167:6: error: implicit declaration of function 'uffd_disable_fault_around' [-Werror,-Wimplicit-function-declaration]
           if (uffd_disable_fault_around(vmf->vma))
               ^
   1 error generated.


vim +/uffd_disable_fault_around +4167 mm/memory.c

  4159	
  4160	/* Return true if we should do read fault-around, false otherwise */
  4161	static inline bool should_fault_around(struct vm_fault *vmf)
  4162	{
  4163		/* No ->map_pages?  No way to fault around... */
  4164		if (!vmf->vma->vm_ops->map_pages)
  4165			return false;
  4166	
> 4167		if (uffd_disable_fault_around(vmf->vma))
  4168			return false;
  4169	
  4170		return fault_around_bytes >> PAGE_SHIFT > 1;
  4171	}
  4172	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org