powerpc/kernel: Check features don't change after patching

Early in boot we binary patch some sections of code based on the CPU and
MMU feature bits. But it is a one-time patching, there is no facility
for repatching the code later if the set of features change.

It is a major bug if the set of features changes after we've done the
code patching - so add a check for it.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/feature-fixups.c

@@ -152,10 +152,19 @@ static void do_final_fixups(void)
 #endif
 }
 
-void apply_feature_fixups(void)
+static unsigned long __initdata saved_cpu_features;
+static unsigned int __initdata saved_mmu_features;
+#ifdef CONFIG_PPC64
+static unsigned long __initdata saved_firmware_features;
+#endif
+
+void __init apply_feature_fixups(void)
 {
 	struct cpu_spec *spec = *PTRRELOC(&cur_cpu_spec);
 
+	*PTRRELOC(&saved_cpu_features) = spec->cpu_features;
+	*PTRRELOC(&saved_mmu_features) = spec->mmu_features;
+
 	/*
 	 * Apply the CPU-specific and firmware specific fixups to kernel text
 	 * (nop out sections not relevant to this CPU or this firmware).
@@ -173,12 +182,28 @@ void apply_feature_fixups(void)
 			 PTRRELOC(&__stop___lwsync_fixup));
 
 #ifdef CONFIG_PPC64
+	saved_firmware_features = powerpc_firmware_features;
 	do_feature_fixups(powerpc_firmware_features,
 			  &__start___fw_ftr_fixup, &__stop___fw_ftr_fixup);
 #endif
 	do_final_fixups();
 }
 
+static int __init check_features(void)
+{
+	WARN(saved_cpu_features != cur_cpu_spec->cpu_features,
+	     "CPU features changed after feature patching!\n");
+	WARN(saved_mmu_features != cur_cpu_spec->mmu_features,
+	     "MMU features changed after feature patching!\n");
+#ifdef CONFIG_PPC64
+	WARN(saved_firmware_features != powerpc_firmware_features,
+	     "Firmware features changed after feature patching!\n");
+#endif
+
+	return 0;
+}
+late_initcall(check_features);
+
 #ifdef CONFIG_FTR_FIXUP_SELFTEST
 
 #define check(x)	\