s390: store breaking event address only for program checks

The principles of operations specifies that the breaking event address
is stored to the address 0x110 in the prefix page only for program checks.
The last branch in user space is lost as soon as a branch in kernel space
is executed after e.g. an svc. This makes it impossible to accurately
maintain the breaking event address for a user space process.

Simplify the code, just copy the current breaking event address from
0x110 to the task structure for program checks from user space.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/entry.S

@@ -103,8 +103,7 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	CHECK_STACK 1<<STACK_SHIFT,\savearea
 	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
 	j	3f
-1:	LAST_BREAK %r14
-	UPDATE_VTIME %r14,%r15,\timer
+1:	UPDATE_VTIME %r14,%r15,\timer
 2:	lg	%r15,__LC_ASYNC_STACK	# load async stack
 3:	la	%r11,STACK_FRAME_OVERHEAD(%r15)
 	.endm
@@ -121,18 +120,6 @@ _PIF_WORK	= (_PIF_PER_TRAP)
 	mvc	__LC_LAST_UPDATE_TIMER(8),\enter_timer
 	.endm
 
-	.macro	LAST_BREAK scratch
-	srag	\scratch,%r10,23
-#ifdef CONFIG_HAVE_MARCH_Z990_FEATURES
-	jz	.+10
-	stg	%r10,__TASK_thread+__THREAD_last_break(%r12)
-#else
-	jz	.+14
-	lghi	\scratch,__TASK_thread
-	stg	%r10,__THREAD_last_break(\scratch,%r12)
-#endif
-	.endm
-
 	.macro REENABLE_IRQS
 	stg	%r8,__LC_RETURN_PSW
 	ni	__LC_RETURN_PSW,0xbf
@@ -278,15 +265,14 @@ ENTRY(system_call)
 	stpt	__LC_SYNC_ENTER_TIMER
 .Lsysc_stmg:
 	stmg	%r8,%r15,__LC_SAVE_AREA_SYNC
-	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_CURRENT
+	lghi	%r13,__TASK_thread
 	lghi	%r14,_PIF_SYSCALL
 .Lsysc_per:
 	lg	%r15,__LC_KERNEL_STACK
 	la	%r11,STACK_FRAME_OVERHEAD(%r15)	# pointer to pt_regs
-	LAST_BREAK %r13
 .Lsysc_vtime:
-	UPDATE_VTIME %r10,%r13,__LC_SYNC_ENTER_TIMER
+	UPDATE_VTIME %r8,%r9,__LC_SYNC_ENTER_TIMER
 	stmg	%r0,%r7,__PT_R0(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_SYNC
 	mvc	__PT_PSW(16,%r11),__LC_SVC_OLD_PSW
@@ -294,12 +280,7 @@ ENTRY(system_call)
 	stg	%r14,__PT_FLAGS(%r11)
 .Lsysc_do_svc:
 	# load address of system call table
-#ifdef CONFIG_HAVE_MARCH_Z990_FEATURES
-	lg	%r10,__TASK_thread+__THREAD_sysc_table(%r12)
-#else
-	lghi	%r13,__TASK_thread
 	lg	%r10,__THREAD_sysc_table(%r13,%r12)
-#endif
 	llgh	%r8,__PT_INT_CODE+2(%r11)
 	slag	%r8,%r8,2			# shift and test for svc 0
 	jnz	.Lsysc_nr_ok
@@ -508,8 +489,7 @@ ENTRY(pgm_check_handler)
 1:	CHECK_STACK STACK_SIZE,__LC_SAVE_AREA_SYNC
 	aghi	%r15,-(STACK_FRAME_OVERHEAD + __PT_SIZE)
 	j	3f
-2:	LAST_BREAK %r14
-	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
+2:	UPDATE_VTIME %r14,%r15,__LC_SYNC_ENTER_TIMER
 	lg	%r15,__LC_KERNEL_STACK
 	lgr	%r14,%r12
 	aghi	%r14,__TASK_thread	# pointer to thread_struct
@@ -518,6 +498,7 @@ ENTRY(pgm_check_handler)
 	jz	3f
 	mvc	__THREAD_trap_tdb(256,%r14),0(%r13)
 3:	la	%r11,STACK_FRAME_OVERHEAD(%r15)
+	stg	%r10,__THREAD_last_break(%r14)
 	stmg	%r0,%r7,__PT_R0(%r11)
 	mvc	__PT_R8(64,%r11),__LC_SAVE_AREA_SYNC
 	stmg	%r8,%r9,__PT_PSW(%r11)
@@ -576,7 +557,6 @@ ENTRY(io_int_handler)
 	STCK	__LC_INT_CLOCK
 	stpt	__LC_ASYNC_ENTER_TIMER
 	stmg	%r8,%r15,__LC_SAVE_AREA_ASYNC
-	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_CURRENT
 	larl	%r13,cleanup_critical
 	lmg	%r8,%r9,__LC_IO_OLD_PSW
@@ -750,7 +730,6 @@ ENTRY(ext_int_handler)
 	STCK	__LC_INT_CLOCK
 	stpt	__LC_ASYNC_ENTER_TIMER
 	stmg	%r8,%r15,__LC_SAVE_AREA_ASYNC
-	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_CURRENT
 	larl	%r13,cleanup_critical
 	lmg	%r8,%r9,__LC_EXT_OLD_PSW
@@ -893,7 +872,6 @@ ENTRY(mcck_int_handler)
 	la	%r1,4095		# revalidate r1
 	spt	__LC_CPU_TIMER_SAVE_AREA-4095(%r1)	# revalidate cpu timer
 	lmg	%r0,%r15,__LC_GPREGS_SAVE_AREA-4095(%r1)# revalidate gprs
-	lg	%r10,__LC_LAST_BREAK
 	lg	%r12,__LC_CURRENT
 	larl	%r13,cleanup_critical
 	lmg	%r8,%r9,__LC_MCK_OLD_PSW
@@ -1088,9 +1066,10 @@ cleanup_critical:
 0:	# check if base register setup + TIF bit load has been done
 	clg	%r9,BASED(.Lcleanup_system_call_insn+16)
 	jhe	0f
-	# set up saved registers r10 and r12
-	stg	%r10,16(%r11)		# r10 last break
-	stg	%r12,32(%r11)		# r12 task struct pointer
+	# set up saved register r12 task struct pointer
+	stg	%r12,32(%r11)
+	# set up saved register r13 __TASK_thread offset
+	mvc	40(8,%r11),BASED(.Lcleanup_system_call_const)
 0:	# check if the user time update has been done
 	clg	%r9,BASED(.Lcleanup_system_call_insn+24)
 	jh	0f
@@ -1107,14 +1086,7 @@ cleanup_critical:
 	stg	%r15,__LC_SYSTEM_TIMER
 0:	# update accounting time stamp
 	mvc	__LC_LAST_UPDATE_TIMER(8),__LC_SYNC_ENTER_TIMER
-	# do LAST_BREAK
-	lg	%r9,16(%r11)
-	srag	%r9,%r9,23
-	jz	0f
-	lgr	%r9,%r12
-	aghi	%r9,__TASK_thread
-	mvc	__THREAD_last_break(8,%r9),16(%r11)
-0:	# set up saved register r11
+	# set up saved register r11
 	lg	%r15,__LC_KERNEL_STACK
 	la	%r9,STACK_FRAME_OVERHEAD(%r15)
 	stg	%r9,24(%r11)		# r11 pt_regs pointer
@@ -1136,6 +1108,8 @@ cleanup_critical:
 	.quad	.Lsysc_per
 	.quad	.Lsysc_vtime+36
 	.quad	.Lsysc_vtime+42
+.Lcleanup_system_call_const:
+	.quad	__TASK_thread
 
 .Lcleanup_sysc_tif:
 	larl	%r9,.Lsysc_tif