Subtract PGDIR_SIZE to work around a bug in free_pgtables

include/asm-ppc64/processor.h

@@ -16,6 +16,7 @@
 #include <asm/ppcdebug.h>
 #include <asm/a.out.h>
 #endif
+#include <asm/pgtable.h>
 #include <asm/ptrace.h>
 #include <asm/types.h>
 
@@ -620,7 +621,8 @@ extern struct task_struct *last_task_used_math;
 
 #ifdef __KERNEL__
 /* 64-bit user address space is 41-bits (2TBs user VM) */
-#define TASK_SIZE_USER64 (0x0000020000000000UL)
+/* Subtract PGDIR_SIZE to work around a bug in free_pgtables */ 
+#define TASK_SIZE_USER64 (0x0000020000000000UL - PGDIR_SIZE)
 
 /* 
  * 32-bit user address space is 4GB - 1 page