Pfnmaps can always be identified with special bits in the ptes/pmds/puds. However that's unnecessary if the vma is stable, and when it's mapped under VM_PFNMAP | VM_IO. Instead of adding similar checks in all the levels for huge pfnmaps, let folio_walk_start() fail even earlier for these mappings. It's also something gup-slow already does, so make them match. Cc: David Hildenbrand <david@xxxxxxxxxx> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> --- mm/pagewalk.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/pagewalk.c b/mm/pagewalk.c index cd79fb3b89e5..fd3965efe773 100644 --- a/mm/pagewalk.c +++ b/mm/pagewalk.c @@ -727,6 +727,11 @@ struct folio *folio_walk_start(struct folio_walk *fw, p4d_t *p4dp; mmap_assert_locked(vma->vm_mm); + + /* It has no folio backing the mappings at all.. */ + if (vma->vm_flags & (VM_IO | VM_PFNMAP)) + return NULL; + vma_pgtable_walk_begin(vma); if (WARN_ON_ONCE(addr < vma->vm_start || addr >= vma->vm_end)) -- 2.45.0
