[PATCH v3 1/5] jump_label: Provide CONFIG-driven build state defaults

[Kees Cook <keescook@xxxxxxxxxxxx>]

Choosing the initial state of static branches changes the assembly
layout (if the condition is expected to be likely, inline, or unlikely,
out of line via a jump). A few places in the kernel use (or could be
using) a CONFIG to choose the default state, so provide the
infrastructure to do this and convert the existing cases (init_on_alloc
and init_on_free) to the new macros.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 include/linux/jump_label.h | 19 +++++++++++++++++++
 include/linux/mm.h         | 12 ++----------
 mm/page_alloc.c            | 12 ++----------
 3 files changed, 23 insertions(+), 20 deletions(-)

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 3526c0aee954..615fdfb871a3 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -382,6 +382,21 @@ struct static_key_false {
 		[0 ... (count) - 1] = STATIC_KEY_FALSE_INIT,	\
 	}
 
+#define _DEFINE_STATIC_KEY_1(name)	DEFINE_STATIC_KEY_TRUE(name)
+#define _DEFINE_STATIC_KEY_0(name)	DEFINE_STATIC_KEY_FALSE(name)
+#define DEFINE_STATIC_KEY_MAYBE(cfg, name)			\
+	__PASTE(_DEFINE_STATIC_KEY_, IS_ENABLED(cfg))(name)
+
+#define _DEFINE_STATIC_KEY_RO_1(name)	DEFINE_STATIC_KEY_TRUE_RO(name)
+#define _DEFINE_STATIC_KEY_RO_0(name)	DEFINE_STATIC_KEY_FALSE_RO(name)
+#define DEFINE_STATIC_KEY_MAYBE_RO(cfg, name)			\
+	__PASTE(_DEFINE_STATIC_KEY_RO_, IS_ENABLED(cfg))(name)
+
+#define _DECLARE_STATIC_KEY_1(name)	DECLARE_STATIC_KEY_TRUE(name)
+#define _DECLARE_STATIC_KEY_0(name)	DECLARE_STATIC_KEY_FALSE(name)
+#define DECLARE_STATIC_KEY_MAYBE(cfg, name)			\
+	__PASTE(_DECLARE_STATIC_KEY_, IS_ENABLED(cfg))(name)
+
 extern bool ____wrong_branch_error(void);
 
 #define static_key_enabled(x)							\
@@ -482,6 +497,10 @@ extern bool ____wrong_branch_error(void);
 
 #endif /* CONFIG_JUMP_LABEL */
 
+#define static_branch_maybe(config, x)					\
+	(IS_ENABLED(config) ? static_branch_likely(x)			\
+			    : static_branch_unlikely(x))
+
 /*
  * Advanced usage; refcount, branch is enabled when: count != 0
  */
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c54fb96cb1e6..059658604dd6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2662,11 +2662,7 @@ static inline void kernel_poison_pages(struct page *page, int numpages,
 					int enable) { }
 #endif
 
-#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
-DECLARE_STATIC_KEY_TRUE(init_on_alloc);
-#else
-DECLARE_STATIC_KEY_FALSE(init_on_alloc);
-#endif
+DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
 static inline bool want_init_on_alloc(gfp_t flags)
 {
 	if (static_branch_unlikely(&init_on_alloc) &&
@@ -2675,11 +2671,7 @@ static inline bool want_init_on_alloc(gfp_t flags)
 	return flags & __GFP_ZERO;
 }
 
-#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
-DECLARE_STATIC_KEY_TRUE(init_on_free);
-#else
-DECLARE_STATIC_KEY_FALSE(init_on_free);
-#endif
+DECLARE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 static inline bool want_init_on_free(void)
 {
 	return static_branch_unlikely(&init_on_free) &&
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3c4eb750a199..1f625e5a03c0 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -135,18 +135,10 @@ unsigned long totalcma_pages __read_mostly;
 
 int percpu_pagelist_fraction;
 gfp_t gfp_allowed_mask __read_mostly = GFP_BOOT_MASK;
-#ifdef CONFIG_INIT_ON_ALLOC_DEFAULT_ON
-DEFINE_STATIC_KEY_TRUE(init_on_alloc);
-#else
-DEFINE_STATIC_KEY_FALSE(init_on_alloc);
-#endif
+DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_ALLOC_DEFAULT_ON, init_on_alloc);
 EXPORT_SYMBOL(init_on_alloc);
 
-#ifdef CONFIG_INIT_ON_FREE_DEFAULT_ON
-DEFINE_STATIC_KEY_TRUE(init_on_free);
-#else
-DEFINE_STATIC_KEY_FALSE(init_on_free);
-#endif
+DEFINE_STATIC_KEY_MAYBE(CONFIG_INIT_ON_FREE_DEFAULT_ON, init_on_free);
 EXPORT_SYMBOL(init_on_free);
 
 static int __init early_init_on_alloc(char *buf)
-- 
2.20.1