[PATCH v1 7/9] mm/memory: factor out common code from vm_normal_page_*()

[David Hildenbrand <david@redhat.com>]

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

To keep it simpler, check the pfn against both zero folios. We could
optimize this, but as it's only for the !CONFIG_ARCH_HAS_PTE_SPECIAL
case, it's not a compelling micro-optimization.

With CONFIG_ARCH_HAS_PTE_SPECIAL we don't have to check anything else,
really.

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.

No functional change intended.

Signed-off-by: David Hildenbrand <david@redhat.com>
---
 mm/memory.c | 183 +++++++++++++++++++++++++++++++---------------------
 1 file changed, 109 insertions(+), 74 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 00ee0df020503..d5f80419989b9 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -596,8 +596,13 @@ static void print_bad_page_map(struct vm_area_struct *vma,
 	add_taint(TAINT_BAD_PAGE, LOCKDEP_NOW_UNRELIABLE);
 }
 
-/*
- * vm_normal_page -- This function gets the "struct page" associated with a pte.
+/**
+ * vm_normal_page_pfn() - Get the "struct page" associated with a PFN in a
+ *			  non-special page table entry.
+ * @vma: The VMA mapping the @pfn.
+ * @addr: The address where the @pfn is mapped.
+ * @pfn: The PFN.
+ * @entry: The page table entry value for error reporting purposes.
  *
  * "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
@@ -609,10 +614,10 @@ static void print_bad_page_map(struct vm_area_struct *vma,
  * (such as GUP) can still identify these mappings 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 (e.g., 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").
@@ -645,15 +650,72 @@ 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.
  *
+ * This function is not expected to be called for obviously special mappings:
+ * when the page table entry has the "special" bit set.
+ *
+ * Return: Returns the "struct page" if this is a "normal" mapping. Returns
+ *	   NULL if this is a "special" mapping.
+ */
+static inline struct page *vm_normal_page_pfn(struct vm_area_struct *vma,
+		unsigned long addr, unsigned long pfn, unsigned long long entry)
+{
+	/*
+	 * With CONFIG_ARCH_HAS_PTE_SPECIAL, any special page table mappings
+	 * (incl. shared zero folios) are marked accordingly and are handled
+	 * by the caller.
+	 */
+	if (!IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
+		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;
+
+				/* 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;
+	}
+
+	/* Cheap check for corrupted page table entries. */
+	if (pfn > highest_memmap_pfn) {
+		print_bad_page_map(vma, addr, entry, NULL);
+		return NULL;
+	}
+	/*
+	 * NOTE! We still have PageReserved() pages in the page tables.
+	 * For example, VDSO mappings can cause them to exist.
+	 */
+	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_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(struct vm_area_struct *vma, unsigned long addr,
 			    pte_t pte)
 {
 	unsigned long pfn = pte_pfn(pte);
 
-	if (IS_ENABLED(CONFIG_ARCH_HAS_PTE_SPECIAL)) {
-		if (likely(!pte_special(pte)))
-			goto check_pfn;
+	if (unlikely(pte_special(pte))) {
 		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))
@@ -664,44 +726,21 @@ struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
 		print_bad_page_map(vma, addr, pte_val(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))
-				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))
-				return NULL;
-		}
-	}
-
-	if (is_zero_pfn(pfn))
-		return NULL;
-
-check_pfn:
-	if (unlikely(pfn > highest_memmap_pfn)) {
-		print_bad_page_map(vma, addr, pte_val(pte), NULL);
-		return NULL;
-	}
-
-	/*
-	 * NOTE! We still have PageReserved() pages in the page tables.
-	 * eg. VDSO mappings can cause them to exist.
-	 */
-out:
-	VM_WARN_ON_ONCE(is_zero_pfn(pfn));
-	return pfn_to_page(pfn);
+	return vm_normal_page_pfn(vma, addr, pfn, pte_val(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_pfn()
+ * for details.
+ *
+ * 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)
 {
@@ -713,6 +752,18 @@ 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 PMD. 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_pmd(struct vm_area_struct *vma, unsigned long addr,
 				pmd_t pmd)
 {
@@ -727,37 +778,21 @@ struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
 		print_bad_page_map(vma, addr, pmd_val(pmd), NULL);
 		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)) {
-		print_bad_page_map(vma, addr, pmd_val(pmd), NULL);
-		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_pfn(vma, addr, pfn, pmd_val(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 PMD. See vm_normal_page_pfn()
+ * for details.
+ *
+ * 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