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/20250811112631.759341-11-david@redhat.com
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Dev Jain <dev.jain@arm.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Juegren Gross <jgross@suse.com>
Cc: Lance Yang <lance.yang@linux.dev>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Mariano Pache <npache@redhat.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

3 files changed, 31 insertions, 10 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b626d1bacef5..8ca7d2fa7134 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2360,6 +2360,8 @@ struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma,
 				  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);
diff --git a/mm/memory.c b/mm/memory.c
index 78af3f243cee..6f806bf3cc99 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -809,6 +809,25 @@ struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma,
 		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
 
 /**
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 648038247a8d..c6753d370ff4 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, addr, 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: