s390: add separate program check exit path

System call and program check handler both use the system call exit
path when returning to previous context. However the program check
handler jumps right to the end of the system call exit path if the
previous context is kernel context.

This lead to the quite odd double disabling of interrupts in the
system call exit path introduced with commit ce9dfafe ("s390:
fix system call exit path").

To avoid that have a separate program check handler exit path if the
previous context is kernel context.
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/entry.S

@@ -430,8 +430,6 @@ ENTRY(system_call)
 	TSTMSK	__LC_CPU_FLAGS,(_CIF_WORK-_CIF_FPU)
 	jnz	.Lsysc_work
 	BPEXIT	__TI_flags(%r12),_TIF_ISOLATE_BP
-.Lsysc_restore:
-	DISABLE_INTS
 	TSTMSK	__LC_CPU_FLAGS, _CIF_FPU
 	jz	.Lsysc_skip_fpu
 	brasl	%r14,load_fpu_regs
@@ -709,10 +707,20 @@ ENTRY(pgm_check_handler)
 .Lpgm_return:
 	LOCKDEP_SYS_EXIT
 	tm	__PT_PSW+1(%r11),0x01	# returning to user ?
-	jno	.Lsysc_restore
+	jno	.Lpgm_restore
 	TSTMSK	__PT_FLAGS(%r11),_PIF_SYSCALL
 	jo	.Lsysc_do_syscall
 	j	.Lsysc_tif
+.Lpgm_restore:
+	DISABLE_INTS
+	TSTMSK	__LC_CPU_FLAGS, _CIF_FPU
+	jz	.Lpgm_skip_fpu
+	brasl	%r14,load_fpu_regs
+.Lpgm_skip_fpu:
+	mvc	__LC_RETURN_PSW(16),__PT_PSW(%r11)
+	stpt	__LC_EXIT_TIMER
+	lmg	%r0,%r15,__PT_R0(%r11)
+	b	__LC_RETURN_LPSWE
 
 #
 # PER event in supervisor state, must be kprobes