[PATCH 3/3] powerpc: Check only single values are passed to CPU/MMU feature checks

[Michael Ellerman]

cpu_has_feature()/mmu_has_feature() are only able to check a single
feature at a time, but there is no enforcement of that.

In fact, as fixed in the previous commit, there was code that was
passing multiple values to cpu_has_feature().

So add a check that only a single feature is passed using popcount.

Note that the test allows 0 or 1 bits to be set, because some code
relies on cpu_has_feature(0) being false, the check with
CPU_FTRS_POSSIBLE ensures that. See for example CPU_FTR_PPC_LE.

Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
---
 arch/powerpc/include/asm/cpu_has_feature.h | 1 +
 arch/powerpc/include/asm/mmu.h             | 1 +
 2 files changed, 2 insertions(+)

diff --git a/arch/powerpc/include/asm/cpu_has_feature.h b/arch/powerpc/include/asm/cpu_has_feature.h
index 92e24e979954..bf8a228229fa 100644
--- a/arch/powerpc/include/asm/cpu_has_feature.h
+++ b/arch/powerpc/include/asm/cpu_has_feature.h
@@ -25,6 +25,7 @@ static __always_inline bool cpu_has_feature(unsigned long feature)
 	int i;
 
 	BUILD_BUG_ON(!__builtin_constant_p(feature));
+	BUILD_BUG_ON(__builtin_popcountl(feature) > 1);
 
 #ifdef CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG
 	if (!static_key_feature_checks_initialized) {
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 4ab9a630d943..eb3065692055 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -247,6 +247,7 @@ static __always_inline bool mmu_has_feature(unsigned long feature)
 	int i;
 
 	BUILD_BUG_ON(!__builtin_constant_p(feature));
+	BUILD_BUG_ON(__builtin_popcountl(feature) > 1);
 
 #ifdef CONFIG_JUMP_LABEL_FEATURE_CHECK_DEBUG
 	if (!static_key_feature_checks_initialized) {
-- 
2.45.0