jump_label: Provide CONFIG-driven build state defaults

As shown in the comment in jump_label.h, choosing the initial state of
static branches changes the assembly layout. If the condition is expected
to be likely it's inline, and if unlikely it is out of line via a jump.

A few places in the kernel use (or could be using) a CONFIG to choose the
default state, which would give a small performance benefit to their
compile-time declared default. Provide the infrastructure to do this.

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20210401232347.2791257-2-keescook@chromium.org

diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index d926912..05f5554 100644 (file)
--- 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,    \
        }
 
                [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)                                                  \
 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 */
 
 
 #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
  */
 /*
  * Advanced usage; refcount, branch is enabled when: count != 0
  */