Re: [PATCH v3 08/22] mm: Allow page table accessors to be non-idempotent

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

Hi Samuel,

kernel test robot noticed the following build errors:

[auto build test ERROR on 24172e0d79900908cf5ebf366600616d29c9b417]

url:    https://github.com/intel-lab-lkp/linux/commits/Samuel-Holland/mm-ptdump-replace-READ_ONCE-with-standard-page-table-accessors/20251113-095117
base:   24172e0d79900908cf5ebf366600616d29c9b417
patch link:    https://lore.kernel.org/r/20251113014656.2605447-9-samuel.holland%40sifive.com
patch subject: [PATCH v3 08/22] mm: Allow page table accessors to be non-idempotent
config: powerpc-allnoconfig (https://download.01.org/0day-ci/archive/20251113/202511131448.ZCsuBlBE-lkp@intel.com/config)
compiler: powerpc-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251113/202511131448.ZCsuBlBE-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511131448.ZCsuBlBE-lkp@intel.com/

All errors (new ones prefixed by >>):

   mm/gup.c: In function 'gup_fast_pte_range':
>> mm/gup.c:2848:9: error: implicit declaration of function 'set_pmd'; did you mean 'set_p4d'? [-Wimplicit-function-declaration]
    2848 |         set_pmd(&pmd, pmd);
         |         ^~~~~~~
         |         set_p4d
--
   mm/pgtable-generic.c: In function '___pte_offset_map':
>> mm/pgtable-generic.c:303:9: error: implicit declaration of function 'set_pmd'; did you mean 'set_p4d'? [-Wimplicit-function-declaration]
     303 |         set_pmd(&pmdval, pmdval);
         |         ^~~~~~~
         |         set_p4d


vim +2848 mm/gup.c

  2819	
  2820	#ifdef CONFIG_ARCH_HAS_PTE_SPECIAL
  2821	/*
  2822	 * GUP-fast relies on pte change detection to avoid concurrent pgtable
  2823	 * operations.
  2824	 *
  2825	 * To pin the page, GUP-fast needs to do below in order:
  2826	 * (1) pin the page (by prefetching pte), then (2) check pte not changed.
  2827	 *
  2828	 * For the rest of pgtable operations where pgtable updates can be racy
  2829	 * with GUP-fast, we need to do (1) clear pte, then (2) check whether page
  2830	 * is pinned.
  2831	 *
  2832	 * Above will work for all pte-level operations, including THP split.
  2833	 *
  2834	 * For THP collapse, it's a bit more complicated because GUP-fast may be
  2835	 * walking a pgtable page that is being freed (pte is still valid but pmd
  2836	 * can be cleared already).  To avoid race in such condition, we need to
  2837	 * also check pmd here to make sure pmd doesn't change (corresponds to
  2838	 * pmdp_collapse_flush() in the THP collapse code path).
  2839	 */
  2840	static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr,
  2841			unsigned long end, unsigned int flags, struct page **pages,
  2842			int *nr)
  2843	{
  2844		int ret = 0;
  2845		pte_t *ptep, *ptem;
  2846	
  2847		/* transform pmd as if &pmd pointed to a hardware page table */
> 2848		set_pmd(&pmd, pmd);
  2849		ptem = ptep = pte_offset_map(&pmd, addr);
  2850		pmd = pmdp_get(&pmd);
  2851		if (!ptep)
  2852			return 0;
  2853		do {
  2854			pte_t pte = ptep_get_lockless(ptep);
  2855			struct page *page;
  2856			struct folio *folio;
  2857	
  2858			/*
  2859			 * Always fallback to ordinary GUP on PROT_NONE-mapped pages:
  2860			 * pte_access_permitted() better should reject these pages
  2861			 * either way: otherwise, GUP-fast might succeed in
  2862			 * cases where ordinary GUP would fail due to VMA access
  2863			 * permissions.
  2864			 */
  2865			if (pte_protnone(pte))
  2866				goto pte_unmap;
  2867	
  2868			if (!pte_access_permitted(pte, flags & FOLL_WRITE))
  2869				goto pte_unmap;
  2870	
  2871			if (pte_special(pte))
  2872				goto pte_unmap;
  2873	
  2874			/* If it's not marked as special it must have a valid memmap. */
  2875			VM_WARN_ON_ONCE(!pfn_valid(pte_pfn(pte)));
  2876			page = pte_page(pte);
  2877	
  2878			folio = try_grab_folio_fast(page, 1, flags);
  2879			if (!folio)
  2880				goto pte_unmap;
  2881	
  2882			if (unlikely(pmd_val(pmd) != pmd_val(pmdp_get(pmdp))) ||
  2883			    unlikely(pte_val(pte) != pte_val(ptep_get(ptep)))) {
  2884				gup_put_folio(folio, 1, flags);
  2885				goto pte_unmap;
  2886			}
  2887	
  2888			if (!gup_fast_folio_allowed(folio, flags)) {
  2889				gup_put_folio(folio, 1, flags);
  2890				goto pte_unmap;
  2891			}
  2892	
  2893			if (!pte_write(pte) && gup_must_unshare(NULL, flags, page)) {
  2894				gup_put_folio(folio, 1, flags);
  2895				goto pte_unmap;
  2896			}
  2897	
  2898			/*
  2899			 * We need to make the page accessible if and only if we are
  2900			 * going to access its content (the FOLL_PIN case).  Please
  2901			 * see Documentation/core-api/pin_user_pages.rst for
  2902			 * details.
  2903			 */
  2904			if ((flags & FOLL_PIN) && arch_make_folio_accessible(folio)) {
  2905				gup_put_folio(folio, 1, flags);
  2906				goto pte_unmap;
  2907			}
  2908			folio_set_referenced(folio);
  2909			pages[*nr] = page;
  2910			(*nr)++;
  2911		} while (ptep++, addr += PAGE_SIZE, addr != end);
  2912	
  2913		ret = 1;
  2914	
  2915	pte_unmap:
  2916		pte_unmap(ptem);
  2917		return ret;
  2918	}
  2919	#else
  2920	

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