Re: [PATCH v8 10/23] mm/shmem: Handle uffd-wp during fork()

[kernel test robot <lkp@intel.com>]

Hi Peter,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on hnaz-mm/master]
[cannot apply to arnd-asm-generic/master linus/master linux/master v5.18-rc1 next-20220405]
[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/intel-lab-lkp/linux/commits/Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20220405-100136
base:   https://github.com/hnaz/linux-mm master
config: ia64-buildonly-randconfig-r005-20220405 (https://download.01.org/0day-ci/archive/20220406/202204061453.OXOxSh6e-lkp@intel.com/config)
compiler: ia64-linux-gcc (GCC) 11.2.0
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/49e56558a1f453907d2813e1ba94d91f9d102e73
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Peter-Xu/userfaultfd-wp-Support-shmem-and-hugetlbfs/20220405-100136
        git checkout 49e56558a1f453907d2813e1ba94d91f9d102e73
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=ia64 SHELL=/bin/bash

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

All warnings (new ones prefixed by >>):

   In file included from arch/ia64/include/asm/pgtable.h:153,
                    from include/linux/pgtable.h:6,
                    from arch/ia64/include/asm/uaccess.h:40,
                    from include/linux/uaccess.h:11,
                    from arch/ia64/include/asm/sections.h:11,
                    from include/linux/interrupt.h:21,
                    from include/linux/kernel_stat.h:9,
                    from mm/memory.c:42:
   arch/ia64/include/asm/mmu_context.h: In function 'reload_context':
   arch/ia64/include/asm/mmu_context.h:127:48: warning: variable 'old_rr4' set but not used [-Wunused-but-set-variable]
     127 |         unsigned long rr0, rr1, rr2, rr3, rr4, old_rr4;
         |                                                ^~~~~~~
   In file included from include/linux/mm_inline.h:9,
                    from mm/memory.c:44:
   include/linux/userfaultfd_k.h: In function 'pte_marker_entry_uffd_wp':
   include/linux/userfaultfd_k.h:260:16: error: implicit declaration of function 'is_pte_marker_entry' [-Werror=implicit-function-declaration]
     260 |         return is_pte_marker_entry(entry) &&
         |                ^~~~~~~~~~~~~~~~~~~
   include/linux/userfaultfd_k.h:261:14: error: implicit declaration of function 'pte_marker_get' [-Werror=implicit-function-declaration]
     261 |             (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
         |              ^~~~~~~~~~~~~~
   include/linux/userfaultfd_k.h:261:38: error: 'PTE_MARKER_UFFD_WP' undeclared (first use in this function)
     261 |             (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
         |                                      ^~~~~~~~~~~~~~~~~~
   include/linux/userfaultfd_k.h:261:38: note: each undeclared identifier is reported only once for each function it appears in
   In file included from include/linux/mm_inline.h:10,
                    from mm/memory.c:44:
   include/linux/swapops.h: At top level:
   include/linux/swapops.h:289:20: error: conflicting types for 'is_pte_marker_entry'; have 'bool(swp_entry_t)' {aka '_Bool(swp_entry_t)'}
     289 | static inline bool is_pte_marker_entry(swp_entry_t entry)
         |                    ^~~~~~~~~~~~~~~~~~~
   In file included from include/linux/mm_inline.h:9,
                    from mm/memory.c:44:
   include/linux/userfaultfd_k.h:260:16: note: previous implicit declaration of 'is_pte_marker_entry' with type 'int()'
     260 |         return is_pte_marker_entry(entry) &&
         |                ^~~~~~~~~~~~~~~~~~~
   In file included from include/linux/mm_inline.h:10,
                    from mm/memory.c:44:
   include/linux/swapops.h:294:26: error: conflicting types for 'pte_marker_get'; have 'pte_marker(swp_entry_t)' {aka 'long unsigned int(swp_entry_t)'}
     294 | static inline pte_marker pte_marker_get(swp_entry_t entry)
         |                          ^~~~~~~~~~~~~~
   In file included from include/linux/mm_inline.h:9,
                    from mm/memory.c:44:
   include/linux/userfaultfd_k.h:261:14: note: previous implicit declaration of 'pte_marker_get' with type 'int()'
     261 |             (pte_marker_get(entry) & PTE_MARKER_UFFD_WP);
         |              ^~~~~~~~~~~~~~
>> mm/memory.c:1238:1: warning: no previous prototype for 'vma_needs_copy' [-Wmissing-prototypes]
    1238 | vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
         | ^~~~~~~~~~~~~~
   In file included from include/linux/mm_inline.h:9,
                    from mm/memory.c:44:
   include/linux/userfaultfd_k.h: In function 'pte_marker_entry_uffd_wp':
   include/linux/userfaultfd_k.h:262:1: error: control reaches end of non-void function [-Werror=return-type]
     262 | }
         | ^
   cc1: some warnings being treated as errors


vim +/vma_needs_copy +1238 mm/memory.c

  1231	
  1232	/*
  1233	 * Return true if the vma needs to copy the pgtable during this fork().  Return
  1234	 * false when we can speed up fork() by allowing lazy page faults later until
  1235	 * when the child accesses the memory range.
  1236	 */
  1237	bool
> 1238	vma_needs_copy(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma)
  1239	{
  1240		/*
  1241		 * Always copy pgtables when dst_vma has uffd-wp enabled even if it's
  1242		 * file-backed (e.g. shmem). Because when uffd-wp is enabled, pgtable
  1243		 * contains uffd-wp protection information, that's something we can't
  1244		 * retrieve from page cache, and skip copying will lose those info.
  1245		 */
  1246		if (userfaultfd_wp(dst_vma))
  1247			return true;
  1248	
  1249		if (src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP))
  1250			return true;
  1251	
  1252		if (src_vma->anon_vma)
  1253			return true;
  1254	
  1255		/*
  1256		 * Don't copy ptes where a page fault will fill them correctly.  Fork
  1257		 * becomes much lighter when there are big shared or private readonly
  1258		 * mappings. The tradeoff is that copy_page_range is more efficient
  1259		 * than faulting.
  1260		 */
  1261		return false;
  1262	}
  1263	

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