arm64: ftrace: stop using kstop_machine to enable/disable tracing

For ftrace on arm64, kstop_machine which is hugely disruptive
to a running system is not needed to convert nops to ftrace calls
or back, because that to be modified instrucions, that NOP, B or BL,
are all safe instructions which called "concurrent modification
and execution of instructions", that can be executed by one
thread of execution as they are being modified by another thread
of execution without requiring explicit synchronization.

Signed-off-by: Li Bin <huawei.libin@huawei.com>
Reviewed-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/kernel/ftrace.c

@@ -93,6 +93,11 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 	return ftrace_modify_code(pc, old, new, true);
 }
 
+void arch_ftrace_update_code(int command)
+{
+	ftrace_modify_all_code(command);
+}
+
 int __init ftrace_dyn_arch_init(void)
 {
 	return 0;