mm: introduce and use vm_normal_page_pud()

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.

Note that we can so far get PUDs with hugetlb, daxfs and PFNMAP entries.

Link: https://lkml.kernel.org/r/[e-mail]
Reviewed-by: Wei Yang <[e-mail]>
Reviewed-by: Oscar Salvador <[e-mail]>
Signed-off-by: David Hildenbrand <[e-mail]>
Reviewed-by: Lorenzo Stoakes <[e-mail]>
Cc: Alistair Popple <[e-mail]>
Cc: Al Viro <[e-mail]>
Cc: Baolin Wang <[e-mail]>
Cc: Barry Song <[e-mail]>
Cc: Christian Brauner <[e-mail]>
Cc: Christophe Leroy <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: David Vrabel <[e-mail]>
Cc: Dev Jain <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Jann Horn <[e-mail]>
Cc: Juegren Gross <[e-mail]>
Cc: Lance Yang <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Madhavan Srinivasan <[e-mail]>
Cc: Mariano Pache <[e-mail]>
Cc: Matthew Wilcox (Oracle) <[e-mail]>
Cc: Michael Ellerman <[e-mail]>
Cc: Michal Hocko <[e-mail]>
Cc: Mike Rapoport <[e-mail]>
Cc: Nicholas Piggin <[e-mail]>
Cc: Oleksandr Tyshchenko <[e-mail]>
Cc: Ryan Roberts <[e-mail]>
Cc: Stefano Stabellini <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Zi Yan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/mm.h

···
 				  unsigned long addr, pmd_t pmd);
 struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
 				pmd_t pmd);
+struct page *vm_normal_page_pud(struct vm_area_struct *vma, unsigned long addr,
+		pud_t pud);
 
 void zap_vma_ptes(struct vm_area_struct *vma, unsigned long address,
 		  unsigned long size);

mm/memory.c

···
 		return page_folio(page);
 	return NULL;
 }
+
+/**
+ * vm_normal_page_pud() - Get the "struct page" associated with a PUD
+ * @vma: The VMA mapping the @pud.
+ * @addr: The address where the @pud is mapped.
+ * @pud: The PUD.
+ *
+ * Get the "struct page" associated with a PUD. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct page" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+struct page *vm_normal_page_pud(struct vm_area_struct *vma,
+		unsigned long addr, pud_t pud)
+{
+	return __vm_normal_page(vma, addr, pud_pfn(pud), pud_special(pud),
+				pud_val(pud), PGTABLE_LEVEL_PUD);
+}
 #endif
 
 /**

mm/pagewalk.c

···
 		fw->pudp = pudp;
 		fw->pud = pud;
 
+		if (pud_none(pud)) {
+			spin_unlock(ptl);
+			goto not_found;
+		} 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, addr, pud);
+			if (page)
+				goto found;
+		}
 		/*
 		 * TODO: FW_MIGRATION support for PUD migration entries
 		 * once there are relevant users.
 		 */
-		if (!pud_present(pud) || pud_special(pud)) {
-			spin_unlock(ptl);
-			goto not_found;
-		} else if (!pud_leaf(pud)) {
-			spin_unlock(ptl);
-			goto pmd_table;
-		}
-		/*
-		 * TODO: vm_normal_page_pud() will be handy once we want to
-		 * support PUD mappings in VM_PFNMAP|VM_MIXEDMAP VMAs.
-		 */
-		page = pud_page(pud);
-		goto found;
+		spin_unlock(ptl);
+		goto not_found;
 	}
 
 pmd_table: