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

[David Hildenbrand <david@xxxxxxxxxx>]

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 <david@xxxxxxxxxx>
---
 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