[PATCH v2 7/9] mm/memory: factor out common code from vm_normal_page_*()

David Hildenbrand
2025-07-17T11:52:36Z

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.

Reviewed-by: Oscar Salvador <osalvador@suse.de>
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 08d16ed7b4cc7..c43ae5e4d7644 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -590,8 +590,13 @@ 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
@@ -603,10 +608,10 @@ 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").
@@ -639,15 +644,72 @@ 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))
@@ -658,44 +720,21 @@ 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)
{
@@ -707,6 +746,18 @@ 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)
{
@@ -721,37 +772,21 @@ 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