1 files changed, 218 insertions, 0 deletions
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
new file mode 100644
index 000000000..f4de473f2
--- /dev/null
+++ b/include/linux/jump_label.h
@@ -0,0 +1,218 @@
+#ifndef _LINUX_JUMP_LABEL_H
+#define _LINUX_JUMP_LABEL_H
+
+/*
+ * Jump label support
+ *
+ * Copyright (C) 2009-2012 Jason Baron <jbaron@redhat.com>
+ * Copyright (C) 2011-2012 Peter Zijlstra <pzijlstr@redhat.com>
+ *
+ * Jump labels provide an interface to generate dynamic branches using
+ * self-modifying code. Assuming toolchain and architecture support, the result
+ * of a "if (static_key_false(&key))" statement is an unconditional branch (which
+ * defaults to false - and the true block is placed out of line).
+ *
+ * However at runtime we can change the branch target using
+ * static_key_slow_{inc,dec}(). These function as a 'reference' count on the key
+ * object, and for as long as there are references all branches referring to
+ * that particular key will point to the (out of line) true block.
+ *
+ * Since this relies on modifying code, the static_key_slow_{inc,dec}() functions
+ * must be considered absolute slow paths (machine wide synchronization etc.).
+ * OTOH, since the affected branches are unconditional, their runtime overhead
+ * will be absolutely minimal, esp. in the default (off) case where the total
+ * effect is a single NOP of appropriate size. The on case will patch in a jump
+ * to the out-of-line block.
+ *
+ * When the control is directly exposed to userspace, it is prudent to delay the
+ * decrement to avoid high frequency code modifications which can (and do)
+ * cause significant performance degradation. Struct static_key_deferred and
+ * static_key_slow_dec_deferred() provide for this.
+ *
+ * Lacking toolchain and or architecture support, jump labels fall back to a simple
+ * conditional branch.
+ *
+ * struct static_key my_key = STATIC_KEY_INIT_TRUE;
+ *
+ *   if (static_key_true(&my_key)) {
+ *   }
+ *
+ * will result in the true case being in-line and starts the key with a single
+ * reference. Mixing static_key_true() and static_key_false() on the same key is not
+ * allowed.
+ *
+ * Not initializing the key (static data is initialized to 0s anyway) is the
+ * same as using STATIC_KEY_INIT_FALSE.
+ */
+
+#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
+# define HAVE_JUMP_LABEL
+#endif
+
+#ifndef __ASSEMBLY__
+
+#include <linux/types.h>
+#include <linux/compiler.h>
+#include <linux/bug.h>
+
+extern bool static_key_initialized;
+
+#define STATIC_KEY_CHECK_USE() WARN(!static_key_initialized,		      \
+				    "%s used before call to jump_label_init", \
+				    __func__)
+
+#ifdef HAVE_JUMP_LABEL
+
+struct static_key {
+	atomic_t enabled;
+/* Set lsb bit to 1 if branch is default true, 0 ot */
+	struct jump_entry *entries;
+#ifdef CONFIG_MODULES
+	struct static_key_mod *next;
+#endif
+};
+
+#else
+struct static_key {
+	atomic_t enabled;
+};
+#endif	/* HAVE_JUMP_LABEL */
+#endif /* __ASSEMBLY__ */
+
+#ifdef HAVE_JUMP_LABEL
+#include <asm/jump_label.h>
+#endif
+
+#ifndef __ASSEMBLY__
+
+enum jump_label_type {
+	JUMP_LABEL_DISABLE = 0,
+	JUMP_LABEL_ENABLE,
+};
+
+struct module;
+
+#include <linux/atomic.h>
+
+static inline int static_key_count(struct static_key *key)
+{
+	return atomic_read(&key->enabled);
+}
+
+#ifdef HAVE_JUMP_LABEL
+
+#define JUMP_LABEL_TYPE_FALSE_BRANCH	0UL
+#define JUMP_LABEL_TYPE_TRUE_BRANCH	1UL
+#define JUMP_LABEL_TYPE_MASK		1UL
+
+static
+inline struct jump_entry *jump_label_get_entries(struct static_key *key)
+{
+	return (struct jump_entry *)((unsigned long)key->entries
+						& ~JUMP_LABEL_TYPE_MASK);
+}
+
+static inline bool jump_label_get_branch_default(struct static_key *key)
+{
+	if (((unsigned long)key->entries & JUMP_LABEL_TYPE_MASK) ==
+	    JUMP_LABEL_TYPE_TRUE_BRANCH)
+		return true;
+	return false;
+}
+
+static __always_inline bool static_key_false(struct static_key *key)
+{
+	return arch_static_branch(key);
+}
+
+static __always_inline bool static_key_true(struct static_key *key)
+{
+	return !static_key_false(key);
+}
+
+extern struct jump_entry __start___jump_table[];
+extern struct jump_entry __stop___jump_table[];
+
+extern void jump_label_init(void);
+extern void jump_label_lock(void);
+extern void jump_label_unlock(void);
+extern void arch_jump_label_transform(struct jump_entry *entry,
+				      enum jump_label_type type);
+extern void arch_jump_label_transform_static(struct jump_entry *entry,
+					     enum jump_label_type type);
+extern int jump_label_text_reserved(void *start, void *end);
+extern void static_key_slow_inc(struct static_key *key);
+extern void static_key_slow_dec(struct static_key *key);
+extern void jump_label_apply_nops(struct module *mod);
+
+#define STATIC_KEY_INIT_TRUE ((struct static_key)		\
+	{ .enabled = ATOMIC_INIT(1),				\
+	  .entries = (void *)JUMP_LABEL_TYPE_TRUE_BRANCH })
+#define STATIC_KEY_INIT_FALSE ((struct static_key)		\
+	{ .enabled = ATOMIC_INIT(0),				\
+	  .entries = (void *)JUMP_LABEL_TYPE_FALSE_BRANCH })
+
+#else  /* !HAVE_JUMP_LABEL */
+
+static __always_inline void jump_label_init(void)
+{
+	static_key_initialized = true;
+}
+
+static __always_inline bool static_key_false(struct static_key *key)
+{
+	if (unlikely(static_key_count(key) > 0))
+		return true;
+	return false;
+}
+
+static __always_inline bool static_key_true(struct static_key *key)
+{
+	if (likely(static_key_count(key) > 0))
+		return true;
+	return false;
+}
+
+static inline void static_key_slow_inc(struct static_key *key)
+{
+	STATIC_KEY_CHECK_USE();
+	atomic_inc(&key->enabled);
+}
+
+static inline void static_key_slow_dec(struct static_key *key)
+{
+	STATIC_KEY_CHECK_USE();
+	atomic_dec(&key->enabled);
+}
+
+static inline int jump_label_text_reserved(void *start, void *end)
+{
+	return 0;
+}
+
+static inline void jump_label_lock(void) {}
+static inline void jump_label_unlock(void) {}
+
+static inline int jump_label_apply_nops(struct module *mod)
+{
+	return 0;
+}
+
+#define STATIC_KEY_INIT_TRUE ((struct static_key) \
+		{ .enabled = ATOMIC_INIT(1) })
+#define STATIC_KEY_INIT_FALSE ((struct static_key) \
+		{ .enabled = ATOMIC_INIT(0) })
+
+#endif	/* HAVE_JUMP_LABEL */
+
+#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
+#define jump_label_enabled static_key_enabled
+
+static inline bool static_key_enabled(struct static_key *key)
+{
+	return static_key_count(key) > 0;
+}
+
+#endif	/* _LINUX_JUMP_LABEL_H */
+
+#endif /* __ASSEMBLY__ */