s390/traps,mm: add conditional trap handlers

Add conditional trap handlers similar to conditional system calls
(COND_SYSCALL), to reduce the number of ifdefs.

Trap handlers which may or may not exist depending on config options
are supposed to have a COND_TRAP entry, which redirects to
default_trap_handler() for non-existent trap handlers during link
time.

This allows to get rid of the secure execution trap handlers for the
!PGSTE case.
Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/entry.h

@@ -26,7 +26,6 @@ void do_dat_exception(struct pt_regs *regs);
 void do_secure_storage_access(struct pt_regs *regs);
 void do_non_secure_storage_access(struct pt_regs *regs);
 void do_secure_storage_violation(struct pt_regs *regs);
-void default_trap_handler(struct pt_regs *regs);
 void do_report_trap(struct pt_regs *regs, int si_signo, int si_code, char *str);
 void kernel_stack_overflow(struct pt_regs * regs);
 void do_signal(struct pt_regs *regs);

arch/s390/kernel/traps.c

@@ -79,7 +79,7 @@ void do_per_trap(struct pt_regs *regs)
 }
 NOKPROBE_SYMBOL(do_per_trap);
 
-void default_trap_handler(struct pt_regs *regs)
+static void default_trap_handler(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
 		report_user_fault(regs, SIGSEGV, 0);
@@ -404,3 +404,12 @@ static void (*pgm_check_table[128])(struct pt_regs *regs) = {
 	[0x40]		= monitor_event_exception,
 	[0x41 ... 0x7f] = default_trap_handler,
 };
+
+#define COND_TRAP(x) asm(			\
+	".weak " __stringify(x) "\n\t"		\
+	".set  " __stringify(x) ","		\
+	__stringify(default_trap_handler))
+
+COND_TRAP(do_secure_storage_access);
+COND_TRAP(do_non_secure_storage_access);
+COND_TRAP(do_secure_storage_violation);

arch/s390/mm/fault.c

@@ -783,6 +783,7 @@ early_initcall(pfault_irq_init);
 #endif /* CONFIG_PFAULT */
 
 #if IS_ENABLED(CONFIG_PGSTE)
+
 void do_secure_storage_access(struct pt_regs *regs)
 {
 	unsigned long addr = regs->int_parm_long & __FAIL_ADDR_MASK;
@@ -859,19 +860,4 @@ void do_secure_storage_violation(struct pt_regs *regs)
 	send_sig(SIGSEGV, current, 0);
 }
 
-#else
-void do_secure_storage_access(struct pt_regs *regs)
-{
-	default_trap_handler(regs);
-}
-
-void do_non_secure_storage_access(struct pt_regs *regs)
-{
-	default_trap_handler(regs);
-}
-
-void do_secure_storage_violation(struct pt_regs *regs)
-{
-	default_trap_handler(regs);
-}
-#endif
+#endif /* CONFIG_PGSTE */