MIPS: asm: pgtable: Add c0 hazards on HTW start/stop sequences

When we use htw_{start,stop}() outside of htw_reset(), we need
to ensure that c0 changes have been propagated properly before
we attempt to continue with subsequence memory operations.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: <stable@vger.kernel.org> # 3.17+
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/9114/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/pgtable.h

@@ -99,16 +99,20 @@ extern void paging_init(void);
 
 #define htw_stop()							\
 do {									\
-	if (cpu_has_htw)						\
+	if (cpu_has_htw) {						\
 		write_c0_pwctl(read_c0_pwctl() &			\
 			       ~(1 << MIPS_PWCTL_PWEN_SHIFT));		\
+		back_to_back_c0_hazard();				\
+	}								\
 } while(0)
 
 #define htw_start()							\
 do {									\
-	if (cpu_has_htw)						\
+	if (cpu_has_htw) {						\
 		write_c0_pwctl(read_c0_pwctl() |			\
 			       (1 << MIPS_PWCTL_PWEN_SHIFT));		\
+		back_to_back_c0_hazard();				\
+	}								\
 } while(0)
 
 
@@ -116,9 +120,7 @@ do {									\
 do {									\
 	if (cpu_has_htw) {						\
 		htw_stop();						\
-		back_to_back_c0_hazard();				\
 		htw_start();						\
-		back_to_back_c0_hazard();				\
 	}								\
 } while(0)