Message-ID: <20250811112631.759341-10-david@redhat.com>
Date: Mon, 11 Aug 2025 13:26:29 +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,
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	linuxppc-dev@...ts.ozlabs.org,
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	Mike Rapoport <rppt@...nel.org>,
	Suren Baghdasaryan <surenb@...gle.com>,
	Michal Hocko <mhocko@...e.com>,
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	Baolin Wang <baolin.wang@...ux.alibaba.com>,
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	Ryan Roberts <ryan.roberts@....com>,
	Dev Jain <dev.jain@....com>,
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	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 v3 09/11] mm/memory: factor out common code from vm_normal_page_*()

Let's reduce the code duplication and factor out the non-pte/pmd related
magic into __vm_normal_page().

To keep it simpler, check the pfn against both zero folios, which
shouldn't really make a difference.

It's a good question if we can even hit the !CONFIG_ARCH_HAS_PTE_SPECIAL
scenario in the PMD case in practice: but doesn't really matter, as
it's now all unified in vm_normal_page_pfn().

Add kerneldoc for all involved functions.

Note that, as a side product, we now:
* Support the find_special_page special thingy also for PMD
* Don't check for is_huge_zero_pfn() anymore if we have
  CONFIG_ARCH_HAS_PTE_SPECIAL and the PMD is not special. The
  VM_WARN_ON_ONCE would catch any abuse

No functional change intended.

Reviewed-by: Oscar Salvador <osalvador@...e.de>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
 mm/memory.c | 186 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 109 insertions(+), 77 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index dc0107354d37b..78af3f243cee7 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -614,8 +614,14 @@ static void print_bad_page_map(struct vm_area_struct *vma,
 #define print_bad_pte(vma, addr, pte, page) \
 	print_bad_page_map(vma, addr, pte_val(pte), page, PGTABLE_LEVEL_PTE)
 
-/*
- * vm_normal_page -- This function gets the "struct page" associated with a pte.
+/**
+ * __vm_normal_page() - Get the "struct page" associated with a page table entry.
+ * @vma: The VMA mapping the page table entry.
+ * @addr: The address where the page table entry is mapped.
+ * @pfn: The PFN stored in the page table entry.
+ * @special: Whether the page table entry is marked "special".
+ * @level: The page table level for error reporting purposes only.
+ * @entry: The page table entry value for error reporting purposes only.
  *
  * "Special" mappings do not wish to be associated with a "struct page" (either
  * it doesn't exist, or it exists but they don't want to touch it). In this
@@ -628,10 +634,10 @@ static void print_bad_page_map(struct vm_area_struct *vma,
  * Selected page table walkers (such as GUP) can still identify mappings of the
  * shared zero folios and work with the underlying "struct page".
  *
- * There are 2 broad cases. Firstly, an architecture may define a pte_special()
- * pte bit, in which case this function is trivial. Secondly, an architecture
- * may not have a spare pte bit, which requires a more complicated scheme,
- * described below.
+ * There are 2 broad cases. Firstly, an architecture may define a "special"
+ * page table entry bit, such as pte_special(), in which case this function is
+ * trivial. Secondly, an architecture may not have a spare page table
+ * entry bit, which requires a more complicated scheme, described below.
  *
  * A raw VM_PFNMAP mapping (ie. one that is not COWed) is always considered a
  * special mapping (even if there are underlying and valid "struct pages").
@@ -664,63 +670,94 @@ static void print_bad_page_map(struct vm_area_struct *vma,
  * don't have to follow the strict linearity rule of PFNMAP mappings in
  * order to support COWable 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(struct vm_area_struct *vma, unsigned long addr,
-			    pte_t pte)
+static inline struct page *__vm_normal_page(struct vm_area_struct *vma,
+		unsigned long addr, unsigned long pfn, bool special,
+		unsigned long long entry, enum pgtable_level level)
 {
-	unsigned long pfn = pte_pfn(pte);
-
 	if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
-		if (likely(!pte_special(pte)))
-			goto check_pfn;
-		if (vma->vm_ops && vma->vm_ops->find_special_page)
-			return vma->vm_ops->find_special_page(vma, addr);
-		if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
-			return NULL;
-		if (is_zero_pfn(pfn))
-			return NULL;
-
-		print_bad_pte(vma, addr, pte, NULL);
-		return NULL;
-	}
-
-	/* !CONFIG_ARCH_HAS_PTE_SPECIAL case follows: */
-
-	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
-		if (vma->vm_flags & VM_MIXEDMAP) {
-			if (!pfn_valid(pfn))
+		if (unlikely(special)) {
+			if (vma->vm_ops && vma->vm_ops->find_special_page)
+				return vma->vm_ops->find_special_page(vma, addr);
+			if (vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))
 				return NULL;
-			if (is_zero_pfn(pfn))
-				return NULL;
-			goto out;
-		} else {
-			unsigned long off;
-			off = (addr - vma->vm_start) >> PAGE_SHIFT;
-			if (pfn == vma->vm_pgoff + off)
-				return NULL;
-			if (!is_cow_mapping(vma->vm_flags))
+			if (is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
 				return NULL;
+
+			print_bad_page_map(vma, addr, entry, NULL, level);
+			return NULL;
 		}
-	}
+		/*
+		 * With CONFIG_ARCH_HAS_PTE_SPECIAL, any special page table
+		 * mappings (incl. shared zero folios) are marked accordingly.
+		 */
+	} else {
+		if (unlikely(vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP))) {
+			if (vma->vm_flags & VM_MIXEDMAP) {
+				/* If it has a "struct page", it's "normal". */
+				if (!pfn_valid(pfn))
+					return NULL;
+			} else {
+				unsigned long off = (addr - vma->vm_start) >> PAGE_SHIFT;
 
-	if (is_zero_pfn(pfn))
-		return NULL;
+				/* Only CoW'ed anon folios are "normal". */
+				if (pfn == vma->vm_pgoff + off)
+					return NULL;
+				if (!is_cow_mapping(vma->vm_flags))
+					return NULL;
+			}
+		}
+
+		if (is_zero_pfn(pfn) || is_huge_zero_pfn(pfn))
+			return NULL;
+	}
 
-check_pfn:
 	if (unlikely(pfn > highest_memmap_pfn)) {
-		print_bad_pte(vma, addr, pte, NULL);
+		/* Corrupted page table entry. */
+		print_bad_page_map(vma, addr, entry, NULL, level);
 		return NULL;
 	}
-
 	/*
 	 * NOTE! We still have PageReserved() pages in the page tables.
-	 * eg. VDSO mappings can cause them to exist.
+	 * For example, VDSO mappings can cause them to exist.
 	 */
-out:
-	VM_WARN_ON_ONCE(is_zero_pfn(pfn));
+	VM_WARN_ON_ONCE(is_zero_pfn(pfn) || is_huge_zero_pfn(pfn));
 	return pfn_to_page(pfn);
 }
 
+/**
+ * vm_normal_page() - Get the "struct page" associated with a PTE
+ * @vma: The VMA mapping the @pte.
+ * @addr: The address where the @pte is mapped.
+ * @pte: The PTE.
+ *
+ * Get the "struct page" associated with a PTE. 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(struct vm_area_struct *vma, unsigned long addr,
+			    pte_t pte)
+{
+	return __vm_normal_page(vma, addr, pte_pfn(pte), pte_special(pte),
+				pte_val(pte), PGTABLE_LEVEL_PTE);
+}
+
+/**
+ * vm_normal_folio() - Get the "struct folio" associated with a PTE
+ * @vma: The VMA mapping the @pte.
+ * @addr: The address where the @pte is mapped.
+ * @pte: The PTE.
+ *
+ * Get the "struct folio" associated with a PTE. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct folio" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
 struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
 			    pte_t pte)
 {
@@ -732,42 +769,37 @@ struct folio *vm_normal_folio(struct vm_area_struct *vma, unsigned long addr,
 }
 
 #ifdef CONFIG_PGTABLE_HAS_HUGE_LEAVES
+/**
+ * vm_normal_page_pmd() - Get the "struct page" associated with a PMD
+ * @vma: The VMA mapping the @pmd.
+ * @addr: The address where the @pmd is mapped.
+ * @pmd: The PMD.
+ *
+ * Get the "struct page" associated with a PTE. 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_pmd(struct vm_area_struct *vma, unsigned long addr,
 				pmd_t pmd)
 {
-	unsigned long pfn = pmd_pfn(pmd);
-
-	if (unlikely(pmd_special(pmd)))
-		return NULL;
-
-	if (unlikely(vma->vm_flags & (VM_PFNMAP|VM_MIXEDMAP))) {
-		if (vma->vm_flags & VM_MIXEDMAP) {
-			if (!pfn_valid(pfn))
-				return NULL;
-			goto out;
-		} else {
-			unsigned long off;
-			off = (addr - vma->vm_start) >> PAGE_SHIFT;
-			if (pfn == vma->vm_pgoff + off)
-				return NULL;
-			if (!is_cow_mapping(vma->vm_flags))
-				return NULL;
-		}
-	}
-
-	if (is_huge_zero_pfn(pfn))
-		return NULL;
-	if (unlikely(pfn > highest_memmap_pfn))
-		return NULL;
-
-	/*
-	 * NOTE! We still have PageReserved() pages in the page tables.
-	 * eg. VDSO mappings can cause them to exist.
-	 */
-out:
-	return pfn_to_page(pfn);
+	return __vm_normal_page(vma, addr, pmd_pfn(pmd), pmd_special(pmd),
+				pmd_val(pmd), PGTABLE_LEVEL_PMD);
 }
 
+/**
+ * vm_normal_folio_pmd() - Get the "struct folio" associated with a PMD
+ * @vma: The VMA mapping the @pmd.
+ * @addr: The address where the @pmd is mapped.
+ * @pmd: The PMD.
+ *
+ * Get the "struct folio" associated with a PTE. See __vm_normal_page()
+ * for details on "normal" and "special" mappings.
+ *
+ * Return: Returns the "struct folio" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
 struct folio *vm_normal_folio_pmd(struct vm_area_struct *vma,
 				  unsigned long addr, pmd_t pmd)
 {
-- 
2.50.1

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