diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index ffc8c13c50e4491941a1f795e2339964305e51da..938dbcd46b97b2827400e2f71813f50bb26622d4 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -114,13 +114,12 @@ static inline void pgd_list_del(pgd_t *pgd)
 
 static void pgd_set_mm(pgd_t *pgd, struct mm_struct *mm)
 {
-	BUILD_BUG_ON(sizeof(virt_to_page(pgd)->index) < sizeof(mm));
-	virt_to_page(pgd)->index = (pgoff_t)mm;
+	virt_to_page(pgd)->pt_mm = mm;
 }
 
 struct mm_struct *pgd_page_get_mm(struct page *page)
 {
-	return (struct mm_struct *)page->index;
+	return page->pt_mm;
 }
 
 static void pgd_ctor(struct mm_struct *mm, pgd_t *pgd)
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 9b45760cc797a7b750a33e414d7e936fde9fad03..811aa0c71e1a0894cf301a63ee2ba60fa33bb2c3 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -139,7 +139,7 @@ struct page {
 			unsigned long _pt_pad_1;	/* compound_head */
 			pgtable_t pmd_huge_pte; /* protected by page->ptl */
 			unsigned long _pt_pad_2;	/* mapping */
-			unsigned long _pt_pad_3;
+			struct mm_struct *pt_mm;	/* x86 pgds only */
 #if ALLOC_SPLIT_PTLOCKS
 			spinlock_t *ptl;
 #else