From c0c6ccd9828c3a1950623b546fa57292a77b5c73 Mon Sep 17 00:00:00 2001 From: "David Hildenbrand (Arm)" Date: Thu, 30 Apr 2026 13:31:22 +0200 Subject: [PATCH] mm: fix __vm_normal_page() to handle missing support for pmd_special()/pud_special() On x86 32-bit with THP enabled, zap_huge_pmd() is seen to generate a "WARNING: mm/memory.c:735 at __vm_normal_page+0x6a/0x7d", from the VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn)); followed by "BUG: Bad rss-counter state"s, then later "BUG: Bad page state"s when reclaim gets to call shrink_huge_zero_folio_scan(). It's as if the _PAGE_SPECIAL bit never got set in the huge_zero pmd: and indeed, whereas pte_special() and pte_mkspecial() are subject to a dedicated CONFIG_ARCH_HAS_PTE_SPECIAL, pmd_special() and pmd_mkspecial() are subject to CONFIG_ARCH_SUPPORTS_PMD_PFNMAP, which is never enabled on any 32-bit architecture. While the problem was exposed through commit d80a9cb1a64a ("mm/huge_memory: add and use normal_or_softleaf_folio_pmd()"), it was an oversight in commit af38538801c6 ("mm/memory: factor out common code from vm_normal_page_*()") and would result in other problems: * huge zero folio accounted in smaps, pagemap (PAGE_IS_FILE) and numamaps as file-backed THP * folio_walk_start() returning the folio even without FW_ZEROPAGE set. Callers seem to tolerate that, though. ... and triggering the VM_WARN_ON_ONE(), although never reported so far. To fix it, teach vm_normal_page_pmd()/vm_normal_page_pud() to consider whether pmd_special/pud_special is actually implemented. Link: https://lore.kernel.org/20260430-pmd_special-v1-1-dbcbcfd72c20@kernel.org Fixes: af38538801c6 ("mm/memory: factor out common code from vm_normal_page_*()") Signed-off-by: David Hildenbrand (Arm) Reported-by: Hugh Dickins Closes: https://lore.kernel.org/r/74a75b59-2e13-3985-ee99-d5521f39df2a@google.com Reported-by: Bibo Mao Closes: https://lore.kernel.org/r/20260430041121.2839350-1-maobibo@loongson.cn Debugged-by: Hugh Dickins Reviewed-by: Lance Yang Tested-by: Bibo Mao Reviewed-by: Baolin Wang Reviewed-by: Oscar Salvador Reviewed-by: Lorenzo Stoakes Cc: Liam R. Howlett Cc: Michal Hocko Cc: Mike Rapoport Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Signed-off-by: Andrew Morton --- mm/memory.c | 22 +++++++++++++++++++--- 1 file changed, 19 insertions(+), 3 deletions(-) diff --git a/mm/memory.c b/mm/memory.c index ea6568571131..c51ad671b95f 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -612,6 +612,21 @@ static void print_bad_page_map(struct vm_area_struct *vma, dump_stack(); add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE); } + +static inline bool pgtable_level_has_pxx_special(enum pgtable_level level) +{ + switch (level) { + case PGTABLE_LEVEL_PTE: + return IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL); + case PGTABLE_LEVEL_PMD: + return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PMD_PFNMAP); + case PGTABLE_LEVEL_PUD: + return IS_ENABLED(CONFIG_ARCH_SUPPORTS_PUD_PFNMAP); + default: + return false; + } +} + #define print_bad_pte(vma, addr, pte, page) \ print_bad_page_map(vma, addr, pte_val(pte), page, PGTABLE_LEVEL_PTE) @@ -684,7 +699,7 @@ static inline struct page *__vm_normal_page(struct vm_area_struct *vma, unsigned long addr, unsigned long pfn, bool special, unsigned long long entry, enum pgtable_level level) { - if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) { + if (pgtable_level_has_pxx_special(level)) { if (unlikely(special)) { #ifdef CONFIG_FIND_NORMAL_PAGE if (vma->vm_ops && vma->vm_ops->find_normal_page) @@ -699,8 +714,9 @@ static inline struct page *__vm_normal_page(struct vm_area_struct *vma, return NULL; } /* - * With CONFIG_ARCH_HAS_PTE_SPECIAL, any special page table - * mappings (incl. shared zero folios) are marked accordingly. + * With working pte_special()/pmd_special()..., any special page + * table mappings (incl. shared zero folios) are marked + * accordingly. */ } else { if (unlikely(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))) {