s390/traps: get rid of magic cast for per code

Add a proper union in lowcore to reflect architecture and get rid of a
"magic" cast in order to read the full per code.

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: hcahca

arch/s390/include/asm/lowcore.h

@@ -43,8 +43,13 @@ struct lowcore {
 	};
 	__u32	data_exc_code;			/* 0x0090 */
 	__u16	mon_class_num;			/* 0x0094 */
-	__u8	per_code;			/* 0x0096 */
-	__u8	per_atmid;			/* 0x0097 */
+	union {
+		struct {
+			__u8	per_code;	/* 0x0096 */
+			__u8	per_atmid;	/* 0x0097 */
+		};
+		__u16 per_code_combined;
+	};
 	__u64	per_address;			/* 0x0098 */
 	__u8	exc_access_id;			/* 0x00a0 */
 	__u8	per_access_id;			/* 0x00a1 */

arch/s390/kernel/traps.c

@@ -322,7 +322,7 @@ void noinstr __do_pgm_check(struct pt_regs *regs)
 
 			set_thread_flag(TIF_PER_TRAP);
 			ev->address = S390_lowcore.per_address;
-			ev->cause = *(u16 *)&S390_lowcore.per_code;
+			ev->cause = S390_lowcore.per_code_combined;
 			ev->paid = S390_lowcore.per_access_id;
 		} else {
 			/* PER event in kernel is kprobes */