s390: correct nospec auto detection init order

With CONFIG_EXPOLINE_AUTO=y the call of spectre_v2_auto_early() via
early_initcall is done *after* the early_param functions. This
overwrites any settings done with the nobp/no_spectre_v2/spectre_v2
parameters. The code patching for the kernel is done after the
evaluation of the early parameters but before the early_initcall
is done. The end result is a kernel image that is patched correctly
but the kernel modules are not.

Make sure that the nospec auto detection function is called before the
early parameters are evaluated and before the code patching is done.

Fixes: 6e179d64126b ("s390: add automatic detection of the spectre defense")
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/include/asm/nospec-branch.h

···
 extern int nospec_disable;
 
 void nospec_init_branches(void);
+void nospec_auto_detect(void);
 void nospec_revert(s32 *start, s32 *end);
 
 #endif /* __ASSEMBLY__ */

arch/s390/kernel/nospec-branch.c

···
 }
 early_param("nospectre_v2", nospectre_v2_setup_early);
 
-static int __init spectre_v2_auto_early(void)
+void __init nospec_auto_detect(void)
 {
 	if (IS_ENABLED(CC_USING_EXPOLINE)) {
 		/*
···
 	 * nobp setting decides what is done, this depends on the
 	 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
 	 */
-	return 0;
 }
-#ifdef CONFIG_EXPOLINE_AUTO
-early_initcall(spectre_v2_auto_early);
-#endif
 
 static int __init spectre_v2_setup_early(char *str)
 {
···
 	if (str && !strncmp(str, "off", 3))
 		nospec_disable = 1;
 	if (str && !strncmp(str, "auto", 4))
-		spectre_v2_auto_early();
+		nospec_auto_detect();
 	return 0;
 }
 early_param("spectre_v2", spectre_v2_setup_early);

arch/s390/kernel/setup.c

···
 	init_mm.end_data = (unsigned long) _edata;
 	init_mm.brk = (unsigned long) _end;
 
+	if (IS_ENABLED(CONFIG_EXPOLINE_AUTO))
+		nospec_auto_detect();
+
 	parse_early_param();
 #ifdef CONFIG_CRASH_DUMP
 	/* Deactivate elfcorehdr= kernel parameter */