[S390] Ensure that vmcore_info pointer is never accessed directly

Because the vmcore_info pointer is not 8 byte aligned it never should
not be accessed directly. The reason is that the compiler assumes that
64 bit pointer are always double word aligned. To ensure save access,
the vmcore_info type in struct lowcore is changed from u64 to an u8[8]
array and a comment is added.
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/lowcore.h

@@ -302,7 +302,12 @@ struct _lowcore {
 	 */
 	__u64	ipib;				/* 0x0e00 */
 	__u32	ipib_checksum;			/* 0x0e08 */
-	__u64	vmcore_info;			/* 0x0e0c */
+	/*
+	 * Because the vmcore_info pointer is not 8 byte aligned it never
+	 * should not be accessed directly. For accessing the pointer, first
+	 * copy it to a local pointer variable.
+	 */
+	__u8	vmcore_info[8];			/* 0x0e0c */
 	__u8	pad_0x0e14[0x0e18-0x0e14];	/* 0x0e14 */
 	__u64	os_info;			/* 0x0e18 */
 	__u8	pad_0x0e20[0x0f00-0x0e20];	/* 0x0e20 */