Futex hash computation requires a mask operation with read-only after
init data that will be converted to a runtime constant in the subsequent
commit.

Introduce runtime_const_mask_32 to further optimize the mask operation
in the futex hash computation hot path.

GCC generates a:

  nilf %r1,<imm32>

to tackle arbitrary 32-bit masks and the same is implemented here.
Immediate patching pattern for __runtime_fixup_mask() has been adopted
from __runtime_fixup_ptr().

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
---
Changelog v2..v3:

o Collected Ack from Heiko after folding in the suggested diff. (Thanks
  a ton!)
---
 arch/s390/include/asm/runtime-const.h | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/s390/include/asm/runtime-const.h b/arch/s390/include/asm/runtime-const.h
index 17878b1d048c..7b71156031ec 100644
--- a/arch/s390/include/asm/runtime-const.h
+++ b/arch/s390/include/asm/runtime-const.h
@@ -33,6 +33,20 @@
 	__ret;							\
 })
 
+#define runtime_const_mask_32(val, sym)				\
+({								\
+	unsigned int __ret = (val);				\
+								\
+	asm_inline(						\
+		"0:	nilf	%[__ret],12\n"			\
+		".pushsection runtime_mask_" #sym ",\"a\"\n"	\
+		".long 0b - .\n"				\
+		".popsection"					\
+		: [__ret] "+d" (__ret)				\
+		: : "cc");					\
+	__ret;							\
+})
+
 #define runtime_const_init(type, sym) do {			\
 	extern s32 __start_runtime_##type##_##sym[];		\
 	extern s32 __stop_runtime_##type##_##sym[];		\
@@ -43,12 +57,12 @@
 			    __stop_runtime_##type##_##sym);	\
 } while (0)
 
-/* 32-bit immediate for iihf and iilf in bits in I2 field */
 static inline void __runtime_fixup_32(u32 *p, unsigned int val)
 {
 	s390_kernel_write(p, &val, sizeof(val));
 }
 
+/* 32-bit immediate for iihf and iilf in bits in I2 field */
 static inline void __runtime_fixup_ptr(void *where, unsigned long val)
 {
 	__runtime_fixup_32(where + 2, val >> 32);
@@ -65,6 +79,12 @@ static inline void __runtime_fixup_shift(void *where, unsigned long val)
 	s390_kernel_write(where, &insn, sizeof(insn));
 }
 
+/* 32-bit immediate for nilf in bits in I2 field */
+static inline void __runtime_fixup_mask(void *where, unsigned long val)
+{
+	__runtime_fixup_32(where + 2, val);
+}
+
 static inline void runtime_const_fixup(void (*fn)(void *, unsigned long),
 				       unsigned long val, s32 *start, s32 *end)
 {
-- 
2.34.1