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>

3 files changed, 26 insertions, 0 deletions

diff --git a/arch/powerpc/Kconfig.debug b/arch/powerpc/Kconfig.debug
index 36d7e345f599..63292f64b25a 100644
--- a/arch/powerpc/Kconfig.debug
+++ b/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
diff --git a/arch/powerpc/include/asm/cpu_has_feature.h b/arch/powerpc/include/asm/cpu_has_feature.h
index 039c011b4252..2ef55f8968a2 100644
--- a/arch/powerpc/include/asm/cpu_has_feature.h
+++ b/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;
 
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 1bf919aafd50..e2fb408f8398 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/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;