diff --git a/arch/s390/include/asm/processor.h b/arch/s390/include/asm/processor.h
index 066b995..db4523f 100644
--- a/arch/s390/include/asm/processor.h
+++ b/arch/s390/include/asm/processor.h
@@ -61,7 +61,7 @@
 extern int get_cpu_capability(unsigned int *);
 
 /*
- * User space process size: 2GB for 31 bit, 4TB for 64 bit.
+ * User space process size: 2GB for 31 bit, 4TB or 8PT for 64 bit.
  */
 #ifndef __s390x__
 
@@ -70,8 +70,7 @@
 
 #else /* __s390x__ */
 
-#define TASK_SIZE_OF(tsk)	(test_tsk_thread_flag(tsk,TIF_31BIT) ? \
-					(1UL << 31) : (1UL << 53))
+#define TASK_SIZE_OF(tsk)	((tsk)->mm->context.asce_limit)
 #define TASK_UNMAPPED_BASE	(test_thread_flag(TIF_31BIT) ? \
 					(1UL << 30) : (1UL << 41))
 #define TASK_SIZE		TASK_SIZE_OF(current)
diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
index 5932a82..346dd0c 100644
--- a/arch/s390/mm/mmap.c
+++ b/arch/s390/mm/mmap.c
@@ -35,7 +35,7 @@
  * Leave an at least ~128 MB hole.
  */
 #define MIN_GAP (128*1024*1024)
-#define MAX_GAP (TASK_SIZE/6*5)
+#define MAX_GAP (STACK_TOP/6*5)
 
 static inline unsigned long mmap_base(void)
 {
@@ -46,7 +46,7 @@
 	else if (gap > MAX_GAP)
 		gap = MAX_GAP;
 
-	return TASK_SIZE - (gap & PAGE_MASK);
+	return STACK_TOP - (gap & PAGE_MASK);
 }
 
 static inline int mmap_is_legacy(void)
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index 0767827..6b6ddc4 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -117,6 +117,7 @@
 		crst_table_init(table, entry);
 		pgd_populate(mm, (pgd_t *) table, (pud_t *) pgd);
 		mm->pgd = (pgd_t *) table;
+		mm->task_size = mm->context.asce_limit;
 		table = NULL;
 	}
 	spin_unlock(&mm->page_table_lock);
@@ -154,6 +155,7 @@
 			BUG();
 		}
 		mm->pgd = (pgd_t *) (pgd_val(*pgd) & _REGION_ENTRY_ORIGIN);
+		mm->task_size = mm->context.asce_limit;
 		crst_table_free(mm, (unsigned long *) pgd);
 	}
 	update_mm(mm, current);