Hi Peter,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on akpm-mm/mm-everything]

url:    https://github.com/intel-lab-lkp/linux/commits/Peter-Xu/mm-migrate-Fix-writable-pte-for-read-migration-entry/20221111-043302
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20221110203132.1498183-3-peterx%40redhat.com
patch subject: [PATCH v2 2/2] mm/uffd: Sanity check write bit for uffd-wp protected ptes
config: x86_64-randconfig-a012
compiler: clang version 14.0.6 (https://github.com/llvm/llvm-project f28c006a5895fc0e329fe15fead81e37457cb1d1)
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
        # https://github.com/intel-lab-lkp/linux/commit/b103eae2926a263a15e262611524ca9efa8b969e
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Peter-Xu/mm-migrate-Fix-writable-pte-for-read-migration-entry/20221111-043302
        git checkout b103eae2926a263a15e262611524ca9efa8b969e
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=x86_64 SHELL=/bin/bash

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

All errors (new ones prefixed by >>):

   In file included from arch/x86/kernel/early_printk.c:11:
   In file included from include/linux/pgtable.h:6:
>> arch/x86/include/asm/pgtable.h:306:2: error: implicit declaration of function 'VM_WARN_ON_ONCE' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
           VM_WARN_ON_ONCE(wp && pte_write(pte));
           ^
   1 error generated.


vim +/VM_WARN_ON_ONCE +306 arch/x86/include/asm/pgtable.h

   290	
   291	#ifdef CONFIG_HAVE_ARCH_USERFAULTFD_WP
   292	static inline int pte_uffd_wp(pte_t pte)
   293	{
   294		bool wp = pte_flags(pte) & _PAGE_UFFD_WP;
   295	
   296		/*
   297		 * Having write bit for wr-protect-marked present ptes is fatal,
   298		 * because it means the uffd-wp bit will be ignored and write will
   299		 * just go through.
   300		 *
   301		 * Use any chance of pgtable walking to verify this (e.g., when
   302		 * page swapped out or being migrated for all purposes). It means
   303		 * something is already wrong.  Tell the admin even before the
   304		 * process crashes. We also nail it with wrong pgtable setup.
   305		 */
 > 306		VM_WARN_ON_ONCE(wp && pte_write(pte));
   307	
   308		return wp;
   309	}
   310	

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