s390: add optimized array_index_mask_nospec

Add an optimized version of the array_index_mask_nospec function for
s390 based on a compare and a subtract with borrow.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/s390/include/asm/barrier.h b/arch/s390/include/asm/barrier.h
index 10432607a573..f9eddbca79d2 100644
--- a/arch/s390/include/asm/barrier.h
+++ b/arch/s390/include/asm/barrier.h
@@ -49,6 +49,30 @@ do {									\
 #define __smp_mb__before_atomic()       barrier()
 #define __smp_mb__after_atomic()        barrier()
 
+/**
+ * array_index_mask_nospec - generate a mask for array_idx() that is
+ * ~0UL when the bounds check succeeds and 0 otherwise
+ * @index: array element index
+ * @size: number of elements in array
+ */
+#define array_index_mask_nospec array_index_mask_nospec
+static inline unsigned long array_index_mask_nospec(unsigned long index,
+                                                    unsigned long size)
+{
+        unsigned long mask;
+
+        if (__builtin_constant_p(size) && size > 0) {
+                asm("   clgr    %2,%1\n"
+                    "   slbgr   %0,%0\n"
+                    :"=d" (mask) : "d" (size-1), "d" (index) :"cc");
+                return mask;
+        }
+        asm("   clgr    %1,%2\n"
+            "   slbgr   %0,%0\n"
+            :"=d" (mask) : "d" (size), "d" (index) :"cc");
+        return ~mask;
+}
+
 #include <asm-generic/barrier.h>
 
 #endif /* __ASM_BARRIER_H */