2 files changed, 46 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2be8d9b5e46f..a25024ff9c11 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1223,6 +1223,9 @@ struct page *follow_page(struct vm_area_struct *, unsigned long address,
 #define FOLL_GET        0x04    /* do get_page on page */
 #define FOLL_ANON       0x08    /* give ZERO_PAGE if no pgtable */
 
+int follow_pfnmap_pte(struct vm_area_struct *vma,
+                                unsigned long address, pte_t *ret_ptep);
+
 typedef int (*pte_fn_t)(pte_t *pte, pgtable_t token, unsigned long addr,
                         void *data);
 extern int apply_to_page_range(struct mm_struct *mm, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index cef95c8c77fa..8ca6bbf34ad6 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1111,6 +1111,49 @@ no_page_table:
         return page;
 }
 
+int follow_pfnmap_pte(struct vm_area_struct *vma, unsigned long address,
+                        pte_t *ret_ptep)
+{
+        pgd_t *pgd;
+        pud_t *pud;
+        pmd_t *pmd;
+        pte_t *ptep, pte;
+        spinlock_t *ptl;
+        struct page *page;
+        struct mm_struct *mm = vma->vm_mm;
+
+        if (!is_pfn_mapping(vma))
+                goto err;
+
+        page = NULL;
+        pgd = pgd_offset(mm, address);
+        if (pgd_none(*pgd) || unlikely(pgd_bad(*pgd)))
+                goto err;
+
+        pud = pud_offset(pgd, address);
+        if (pud_none(*pud) || unlikely(pud_bad(*pud)))
+                goto err;
+
+        pmd = pmd_offset(pud, address);
+        if (pmd_none(*pmd) || unlikely(pmd_bad(*pmd)))
+                goto err;
+
+        ptep = pte_offset_map_lock(mm, pmd, address, &ptl);
+
+        pte = *ptep;
+        if (!pte_present(pte))
+                goto err_unlock;
+
+        *ret_ptep = pte;
+        pte_unmap_unlock(ptep, ptl);
+        return 0;
+
+err_unlock:
+        pte_unmap_unlock(ptep, ptl);
+err:
+        return -EINVAL;
+}
+
 /* Can we do the FOLL_ANON optimization? */
 static inline int use_zero_page(struct vm_area_struct *vma)
 {