As shown in jump_label.h[1], 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.
[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/linux/jump_label.h?h=v5.11#n398
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Kees Cook <[email protected]>
---
include/linux/jump_label.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index d92691262f51..05f5554d860f 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
*/
--
2.25.1
The following commit has been merged into the x86/entry branch of tip:
Commit-ID: 0d66ccc1627013c95f1e7ef10b95b8451cd7834e
Gitweb: https://git.kernel.org/tip/0d66ccc1627013c95f1e7ef10b95b8451cd7834e
Author: Kees Cook <[email protected]>
AuthorDate: Thu, 01 Apr 2021 16:23:42 -07:00
Committer: Thomas Gleixner <[email protected]>
CommitterDate: Thu, 08 Apr 2021 14:05:19 +02:00
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 <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
---
include/linux/jump_label.h | 19 +++++++++++++++++++
1 file changed, 19 insertions(+)
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index d926912..05f5554 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
*/