powerpc/mm: Catch usage of cpu/mmu_has_feature() before jump label init

This allows us to catch incorrect usage of cpu_has_feature() and
mmu_has_feature() prior to jump labels being initialised.

mpe: Use printk() and dump_stack() rather than WARN_ON(), because
WARN_ON() may not work this early in boot. Rename the Kconfig.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/Kconfig.debug

@@ -69,6 +69,16 @@ config JUMP_LABEL_FEATURE_CHECKS
 	  feature checks. This should generate more optimal code for those
 	  checks.
 
+config JUMP_LABEL_FEATURE_CHECK_DEBUG
+	bool "Do extra check on feature fixup calls"
+	depends on DEBUG_KERNEL && JUMP_LABEL_FEATURE_CHECKS
+	default n
+	help
+	  This tries to catch incorrect usage of cpu_has_feature() and
+	  mmu_has_feature() in the code.
+
+	  If you don't know what this means, say N.
+
 config FTR_FIXUP_SELFTEST
 	bool "Run self-tests of the feature-fixup code"
 	depends on DEBUG_KERNEL

arch/powerpc/include/asm/cpu_has_feature.h

@@ -25,6 +25,14 @@ static __always_inline bool cpu_has_feature(unsigned long feature)
 
 	BUILD_BUG_ON(!__builtin_constant_p(feature));
 
+#ifdef CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG
+	if (!static_key_initialized) {
+		printk("Warning! cpu_has_feature() used prior to jump label init!\n");
+		dump_stack();
+		return early_cpu_has_feature(feature);
+	}
+#endif
+
 	if (CPU_FTRS_ALWAYS & feature)
 		return true;
 

arch/powerpc/include/asm/mmu.h

@@ -156,6 +156,14 @@ static __always_inline bool mmu_has_feature(unsigned long feature)
 
 	BUILD_BUG_ON(!__builtin_constant_p(feature));
 
+#ifdef CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG
+	if (!static_key_initialized) {
+		printk("Warning! mmu_has_feature() used prior to jump label init!\n");
+		dump_stack();
+		return early_mmu_has_feature(feature);
+	}
+#endif
+
 	if (!(MMU_FTRS_POSSIBLE & feature))
 		return false;