s390/vdso: map vdso above stack

In the current code vdso is mapped below the stack. This is
problematic when programs mapped to the top of the address space
are allocating a lot of memory, because the heap will clash with
the vdso. To avoid this map the vdso above the stack and move
STACK_TOP so that it all fits into three level paging.
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/include/asm/processor.h

@@ -95,9 +95,10 @@ unsigned long vdso_size(void);
 					(_REGION3_SIZE >> 1) : (_REGION2_SIZE >> 1))
 #define TASK_SIZE_MAX		(-PAGE_SIZE)
 
-#define STACK_TOP		(test_thread_flag(TIF_31BIT) ? \
-					_REGION3_SIZE : _REGION2_SIZE)
-#define STACK_TOP_MAX		_REGION2_SIZE
+#define VDSO_BASE		(STACK_TOP + PAGE_SIZE)
+#define VDSO_LIMIT		(test_thread_flag(TIF_31BIT) ? _REGION3_SIZE : _REGION2_SIZE)
+#define STACK_TOP		(VDSO_LIMIT - vdso_size() - PAGE_SIZE)
+#define STACK_TOP_MAX		(_REGION2_SIZE - vdso_size() - PAGE_SIZE)
 
 #define HAVE_ARCH_PICK_MMAP_LAYOUT
 

arch/s390/kernel/vdso.c

@@ -221,7 +221,7 @@ unsigned long vdso_size(void)
 
 int arch_setup_additional_pages(struct linux_binprm *bprm, int uses_interp)
 {
-	return map_vdso(0, vdso_size());
+	return map_vdso(VDSO_BASE, vdso_size());
 }
 
 static struct page ** __init vdso_setup_pages(void *start, void *end)