powerpc/code-patching: Use jump_label to check if poking_init() is done

It's only during early startup that poking_init() is not done yet,
for instance when calling ftrace_init().

Once poking_init() has been called there must be a poking area, no
need to check it everytime patch_instruction() is called.

ftrace activation time is reduced by 7% with the change on an 8xx.

Signed-off-by: Christophe Leroy <[e-mail]>
Signed-off-by: Michael Ellerman <[e-mail]>
Link: https://lore.kernel.org/r/8d6088ac[e-mail]

arch/powerpc/lib/code-patching.c

···
 	return 0;
 }
 
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(poking_init_done);
+
 /*
  * Although BUG_ON() is rude, in this case it should only happen if ENOMEM, and
  * we judge it as being preferable to a kernel that will crash later when
···
 	BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
 		"powerpc/text_poke:online", text_area_cpu_up,
 		text_area_cpu_down));
+	static_branch_enable(&poking_init_done);
 }
 
 /*
···
 	 * when text_poke_area is not ready, but we still need
 	 * to allow patching. We just do the plain old patching
 	 */
-	if (!this_cpu_read(text_poke_area))
+	if (!static_branch_likely(&poking_init_done))
 		return raw_patch_instruction(addr, instr);
 
 	local_irq_save(flags);