s390: add support for BEAR enhancement facility

The Breaking-Event-Address-Register (BEAR) stores the address of the
last breaking event instruction. Breaking events are usually instructions
that change the program flow - for example branches, and instructions
that modify the address in the PSW like lpswe. This is useful for debugging
wild branches, because one could easily figure out where the wild branch
was originating from.

What is problematic is that lpswe is considered a breaking event, and
therefore overwrites BEAR on kernel exit. The BEAR enhancement facility
adds new instructions that allow to save/restore BEAR and also an lpswey
instruction that doesn't cause a breaking event. So we can save BEAR on
kernel entry and restore it on exit to user space.

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

arch/s390/include/asm/lowcore.h

@@ -93,9 +93,10 @@ struct lowcore {
 	psw_t	return_psw;			/* 0x0290 */
 	psw_t	return_mcck_psw;		/* 0x02a0 */
 
+	__u64	last_break;			/* 0x02b0 */
+
 	/* CPU accounting and timing values. */
-	__u64	sys_enter_timer;		/* 0x02b0 */
-	__u8	pad_0x02b8[0x02c0-0x02b8];	/* 0x02b8 */
+	__u64	sys_enter_timer;		/* 0x02b8 */
 	__u64	mcck_enter_timer;		/* 0x02c0 */
 	__u64	exit_timer;			/* 0x02c8 */
 	__u64	user_timer;			/* 0x02d0 */
@@ -188,7 +189,7 @@ struct lowcore {
 	__u32	tod_progreg_save_area;		/* 0x1324 */
 	__u32	cpu_timer_save_area[2];		/* 0x1328 */
 	__u32	clock_comp_save_area[2];	/* 0x1330 */
-	__u8	pad_0x1338[0x1340-0x1338];	/* 0x1338 */
+	__u64	last_break_save_area;		/* 0x1338 */
 	__u32	access_regs_save_area[16];	/* 0x1340 */
 	__u64	cregs_save_area[16];		/* 0x1380 */
 	__u8	pad_0x1400[0x1800-0x1400];	/* 0x1400 */