linux-kernel - [PATCH v2 8/9] mm: introduce and use vm_normal_page

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Message-ID: <20250717115212.1825089-9-david@redhat.com>
Date: Thu, 17 Jul 2025 13:52:11 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
	xen-devel@...ts.xenproject.org,
	linux-fsdevel@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	David Hildenbrand <david@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Juergen Gross <jgross@...e.com>,
	Stefano Stabellini <sstabellini@...nel.org>,
	Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
	Dan Williams <dan.j.williams@...el.com>,
	Matthew Wilcox <willy@...radead.org>,
	Jan Kara <jack@...e.cz>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
	Zi Yan <ziy@...dia.com>,
	Baolin Wang <baolin.wang@...ux.alibaba.com>,
	Nico Pache <npache@...hat.com>,
	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
	Barry Song <baohua@...nel.org>,
	Jann Horn <jannh@...gle.com>,
	Pedro Falcato <pfalcato@...e.de>,
	Hugh Dickins <hughd@...gle.com>,
	Oscar Salvador <osalvador@...e.de>,
	Lance Yang <lance.yang@...ux.dev>
Subject: [PATCH v2 8/9] 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.

Reviewed-by: Oscar Salvador <osalvador@...e.de>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 include/linux/mm.h |  2 ++
 mm/memory.c        | 27 +++++++++++++++++++++++++++
 mm/pagewalk.c      | 20 ++++++++++----------
 3 files changed, 39 insertions(+), 10 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index abc47f1f307fb..0eb991262fbbf 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2349,6 +2349,8 @@ 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 c43ae5e4d7644..00a0d7ae3ba4a 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -796,6 +796,33 @@ 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_pfn()
+ * for details.
+ *
+ * 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)
+{
+	unsigned long pfn = pud_pfn(pud);
+
+	if (unlikely(pud_special(pud))) {
+		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
+			return NULL;
+
+		print_bad_page_map(vma, addr, pud_val(pud), NULL);
+		return NULL;
+	}
+	return vm_normal_page_pfn(vma, addr, pfn, pud_val(pud));
+}
 #endif
 
 /**
diff --git a/mm/pagewalk.c b/mm/pagewalk.c
index 648038247a8d2..c6753d370ff4e 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:
-- 
2.50.1