init/main.c: fix misleading "This architecture does not have kernel memory protection" message

This message leads to thinking that memory protection is not implemented
for the said architecture, whereas absence of CONFIG_STRICT_KERNEL_RWX
only means that memory protection has not been selected at compile time.

Don't print this message when CONFIG_ARCH_HAS_STRICT_KERNEL_RWX is
selected by the architecture.  Instead, print "Kernel memory protection
not selected by kernel config."

Link: http://lkml.kernel.org/r/62477e446d9685459d4f27d193af6ff1bd69d55f.1578557581.git.christophe.leroy@c-s.fr
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

init/main.c

@@ -1104,6 +1104,11 @@ static void mark_readonly(void)
 	} else
 		pr_info("Kernel memory protection disabled.\n");
 }
+#elif defined(CONFIG_ARCH_HAS_STRICT_KERNEL_RWX)
+static inline void mark_readonly(void)
+{
+	pr_warn("Kernel memory protection not selected by kernel config.\n");
+}
 #else
 static inline void mark_readonly(void)
 {