[PATCH RFC 13/14] mm: introduce and use vm_normal_page_pud()

[David Hildenbrand]

Let's introduce vm_normal_page_pud(), which ends up being fairly simple
because of our new common helpers and there not being a PUD-sized zero
folio.

Use vm_normal_page_pud() in folio_walk_start() to resolve a TODO,
structuring the code like the other (pmd/pte) cases. Defer
introducing vm_normal_folio_pud() until really used.

Signed-off-by: David Hildenbrand <da...@redhat.com>
---
 include/linux/mm.h |  1 +
 mm/memory.c        | 11 +++++++++++
 mm/pagewalk.c      | 20 ++++++++++----------
 3 files changed, 22 insertions(+), 10 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ef709457c7076..022e8ef2c78ef 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2361,6 +2361,7 @@ struct page *vm_normal_page(struct vm_area_struct *vma, 
unsigned long addr,
                             pte_t pte);
 struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma, pmd_t pmd);
 struct page *vm_normal_page_pmd(struct vm_area_struct *vma, pmd_t pmd);
+struct page *vm_normal_page_pud(struct vm_area_struct *vma, pud_t pud);
 
 void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
                  unsigned long size);
diff --git a/mm/memory.c b/mm/memory.c
index 34f961024e8e6..6c65f51248250 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -683,6 +683,17 @@ struct folio *vm_normal_folio_pmd(struct vm_area_struct 
*vma, pmd_t pmd)
                return page_folio(page);
        return NULL;
 }
+
+struct page *vm_normal_page_pud(struct vm_area_struct *vma, pud_t pud)
+{
+       unsigned long pfn = pud_pfn(pud);
+
+       if (unlikely(pud_special(pud))) {
+               VM_WARN_ON_ONCE(!(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)));
+               return NULL;
+       }
+       return vm_normal_page_pfn(vma, pfn);
+}
 #endif
 
 /**
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 0edb7240d090c..8bd95cf326872 100644
--- a/mm/pagewalk.c
+++ b/mm/pagewalk.c
@@ -902,23 +902,23 @@ struct folio *folio_walk_start(struct folio_walk *fw,
                fw->pudp = pudp;
                fw->pud = pud;
 
-               /*
-                * TODO: FW_MIGRATION support for PUD migration entries
-                * once there are relevant users.
-                */
-               if (!pud_present(pud) || pud_special(pud)) {
+               if (pud_none(pud)) {
                        spin_unlock(ptl);
                        goto not_found;
-               } else if (!pud_leaf(pud)) {
+               } else if (pud_present(pud) && !pud_leaf(pud)) {
                        spin_unlock(ptl);
                        goto pmd_table;
+               } else if (pud_present(pud)) {
+                       page = vm_normal_page_pud(vma, pud);
+                       if (page)
+                               goto found;
                }
                /*
-                * TODO: vm_normal_page_pud() will be handy once we want to
-                * support PUD mappings in VM_PFNMAP|VM_MIXEDMAP VMAs.
+                * TODO: FW_MIGRATION support for PUD migration entries
+                * once there are relevant users.
                 */
-               page = pud_page(pud);
-               goto found;
+               spin_unlock(ptl);
+               goto not_found;
        }
 
 pmd_table:
-- 
2.49.0