jump_label.h

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/* SPDX-License-Identifier: GPL-2.0 */
#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 Red Hat, Inc., Peter Zijlstra
 *
 * DEPRECATED API:
 *
 * The use of 'struct static_key' directly, is now DEPRECATED. In addition
 * static_key_{true,false}() is also DEPRECATED. IE DO NOT use the following:
 *
 * struct static_key false = STATIC_KEY_INIT_FALSE;
 * struct static_key true = STATIC_KEY_INIT_TRUE;
 * static_key_true()
 * static_key_false()
 *
 * The updated API replacements are:
 *
 * DEFINE_STATIC_KEY_TRUE(key);
 * DEFINE_STATIC_KEY_FALSE(key);
 * DEFINE_STATIC_KEY_ARRAY_TRUE(keys, count);
 * DEFINE_STATIC_KEY_ARRAY_FALSE(keys, count);
 * static_branch_likely()
 * static_branch_unlikely()
 *
 * Jump labels provide an interface to generate dynamic branches using
 * self-modifying code. Assuming toolchain and architecture support, if we
 * define a "key" that is initially false via "DEFINE_STATIC_KEY_FALSE(key)",
 * an "if (static_branch_unlikely(&key))" statement is an unconditional branch
 * (which defaults to false - and the true block is placed out of line).
 * Similarly, we can define an initially true key via
 * "DEFINE_STATIC_KEY_TRUE(key)", and use it in the same
 * "if (static_branch_unlikely(&key))", in which case we will generate an
 * unconditional branch to the out-of-line true branch. Keys that are
 * initially true or false can be using in both static_branch_unlikely()
 * and static_branch_likely() statements.
 *
 * At runtime we can change the branch target by setting the key
 * to true via a call to static_branch_enable(), or false using
 * static_branch_disable(). If the direction of the branch is switched by
 * these calls then we run-time modify the branch target via a
 * no-op -> jump or jump -> no-op conversion. For example, for an
 * initially false key that is used in an "if (static_branch_unlikely(&key))"
 * statement, setting the key to true requires us to patch in a jump
 * to the out-of-line of true branch.
 *
 * In addition to static_branch_{enable,disable}, we can also reference count
 * the key or branch direction via static_branch_{inc,dec}. Thus,
 * static_branch_inc() can be thought of as a 'make more true' and
 * static_branch_dec() as a 'make more false'.
 *
 * Since this relies on modifying code, the branch modifying 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, static keys fall back to a
 * simple conditional branch.
 *
 * Additional babbling in: Documentation/staging/static-keys.rst
 */
 
#ifndef __ASSEMBLY__
 
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/cleanup.h>
 
extern bool static_key_initialized;
 
#define STATIC_KEY_CHECK_USE(key) WARN(!static_key_initialized,           \
                    "%s(): static key '%pS' used before call to jump_label_init()", \
                    __func__, (key))
 
struct static_key {
    atomic_t enabled;
#ifdef CONFIG_JUMP_LABEL
/*
 * bit 0 => 1 if key is initially true
 *      0 if initially false
 * bit 1 => 1 if points to struct static_key_mod
 *      0 if points to struct jump_entry
 */
    union {
        unsigned long type;
        struct jump_entry *entries;
        struct static_key_mod *next;
    };
#endif  /* CONFIG_JUMP_LABEL */
};
 
#endif /* __ASSEMBLY__ */
 
#ifdef CONFIG_JUMP_LABEL
#include <asm/jump_label.h>
 
#ifndef __ASSEMBLY__
#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
 
struct jump_entry {
    s32 code;
    s32 target;
    long key;   // key may be far away from the core kernel under KASLR
};
 
static inline unsigned long jump_entry_code(const struct jump_entry *entry)
{
    return (unsigned long)&entry->code + entry->code;
}
 
static inline unsigned long jump_entry_target(const struct jump_entry *entry)
{
    return (unsigned long)&entry->target + entry->target;
}
 
static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
{
    long offset = entry->key & ~3L;
 
    return (struct static_key *)((unsigned long)&entry->key + offset);
}
 
#else
 
static inline unsigned long jump_entry_code(const struct jump_entry *entry)
{
    return entry->code;
}
 
static inline unsigned long jump_entry_target(const struct jump_entry *entry)
{
    return entry->target;
}
 
static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
{
    return (struct static_key *)((unsigned long)entry->key & ~3UL);
}
 
#endif
 
static inline bool jump_entry_is_branch(const struct jump_entry *entry)
{
    return (unsigned long)entry->key & 1UL;
}
 
static inline bool jump_entry_is_init(const struct jump_entry *entry)
{
    return (unsigned long)entry->key & 2UL;
}
 
static inline void jump_entry_set_init(struct jump_entry *entry, bool set)
{
    if (set)
        entry->key |= 2;
    else
        entry->key &= ~2;
}
 
static inline int jump_entry_size(struct jump_entry *entry)
{
#ifdef JUMP_LABEL_NOP_SIZE
    return JUMP_LABEL_NOP_SIZE;
#else
    return arch_jump_entry_size(entry);
#endif
}
 
#endif
#endif
 
#ifndef __ASSEMBLY__
 
enum jump_label_type {
    JUMP_LABEL_NOP = 0,
    JUMP_LABEL_JMP,
};
 
struct module;
 
#ifdef CONFIG_JUMP_LABEL
 
#define JUMP_TYPE_FALSE     0UL
#define JUMP_TYPE_TRUE      1UL
#define JUMP_TYPE_LINKED    2UL
#define JUMP_TYPE_MASK      3UL
 
static __always_inline bool static_key_false(struct static_key *key)
{
    return arch_static_branch(key, false);
}
 
static __always_inline bool static_key_true(struct static_key *key)
{
    return !arch_static_branch(key, true);
}
 
extern struct jump_entry __start___jump_table[];
extern struct jump_entry __stop___jump_table[];
 
extern void jump_label_init(void);
extern void jump_label_init_ro(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 bool arch_jump_label_transform_queue(struct jump_entry *entry,
                        enum jump_label_type type);
extern void arch_jump_label_transform_apply(void);
extern int jump_label_text_reserved(void *start, void *end);
extern bool static_key_slow_inc(struct static_key *key);
extern bool static_key_fast_inc_not_disabled(struct static_key *key);
extern void static_key_slow_dec(struct static_key *key);
extern bool static_key_slow_inc_cpuslocked(struct static_key *key);
extern void static_key_slow_dec_cpuslocked(struct static_key *key);
extern int static_key_count(struct static_key *key);
extern void static_key_enable(struct static_key *key);
extern void static_key_disable(struct static_key *key);
extern void static_key_enable_cpuslocked(struct static_key *key);
extern void static_key_disable_cpuslocked(struct static_key *key);
extern enum jump_label_type jump_label_init_type(struct jump_entry *entry);
 
#define STATIC_KEY_INIT_TRUE                    \
    { .enabled = ATOMIC_INIT(1),                \
      .type = JUMP_TYPE_TRUE }
#define STATIC_KEY_INIT_FALSE                   \
    { .enabled = ATOMIC_INIT(0),                \
      .type = JUMP_TYPE_FALSE }
 
#else  /* !CONFIG_JUMP_LABEL */
 
#include <linux/atomic.h>
#include <linux/bug.h>
 
static __always_inline int static_key_count(struct static_key *key)
{
    return raw_atomic_read(&key->enabled);
}
 
static __always_inline void jump_label_init(void)
{
    static_key_initialized = true;
}
 
static __always_inline void jump_label_init_ro(void) { }
 
static __always_inline bool static_key_false(struct static_key *key)
{
    if (unlikely_notrace(static_key_count(key) > 0))
        return true;
    return false;
}
 
static __always_inline bool static_key_true(struct static_key *key)
{
    if (likely_notrace(static_key_count(key) > 0))
        return true;
    return false;
}
 
static inline bool static_key_fast_inc_not_disabled(struct static_key *key)
{
    int v;
 
    STATIC_KEY_CHECK_USE(key);
    /*
     * Prevent key->enabled getting negative to follow the same semantics
     * as for CONFIG_JUMP_LABEL=y, see kernel/jump_label.c comment.
     */
    v = atomic_read(&key->enabled);
    do {
        if (v < 0 || (v + 1) < 0)
            return false;
    } while (!likely(atomic_try_cmpxchg(&key->enabled, &v, v + 1)));
    return true;
}
#define static_key_slow_inc(key)    static_key_fast_inc_not_disabled(key)
 
static inline void static_key_slow_dec(struct static_key *key)
{
    STATIC_KEY_CHECK_USE(key);
    atomic_dec(&key->enabled);
}
 
#define static_key_slow_inc_cpuslocked(key) static_key_slow_inc(key)
#define static_key_slow_dec_cpuslocked(key) static_key_slow_dec(key)
 
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 void static_key_enable(struct static_key *key)
{
    STATIC_KEY_CHECK_USE(key);
 
    if (atomic_read(&key->enabled) != 0) {
        WARN_ON_ONCE(atomic_read(&key->enabled) != 1);
        return;
    }
    atomic_set(&key->enabled, 1);
}
 
static inline void static_key_disable(struct static_key *key)
{
    STATIC_KEY_CHECK_USE(key);
 
    if (atomic_read(&key->enabled) != 1) {
        WARN_ON_ONCE(atomic_read(&key->enabled) != 0);
        return;
    }
    atomic_set(&key->enabled, 0);
}
 
#define static_key_enable_cpuslocked(k)     static_key_enable((k))
#define static_key_disable_cpuslocked(k)    static_key_disable((k))
 
#define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
#define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
 
#endif  /* CONFIG_JUMP_LABEL */
 
DEFINE_LOCK_GUARD_0(jump_label_lock, jump_label_lock(), jump_label_unlock())
 
#define STATIC_KEY_INIT STATIC_KEY_INIT_FALSE
#define jump_label_enabled static_key_enabled
 
/* -------------------------------------------------------------------------- */
 
/*
 * Two type wrappers around static_key, such that we can use compile time
 * type differentiation to emit the right code.
 *
 * All the below code is macros in order to play type games.
 */
 
struct static_key_true {
    struct static_key key;
};
 
struct static_key_false {
    struct static_key key;
};
 
#define STATIC_KEY_TRUE_INIT  (struct static_key_true) { .key = STATIC_KEY_INIT_TRUE,  }
#define STATIC_KEY_FALSE_INIT (struct static_key_false){ .key = STATIC_KEY_INIT_FALSE, }
 
#define DEFINE_STATIC_KEY_TRUE(name)    \
    struct static_key_true name = STATIC_KEY_TRUE_INIT
 
#define DEFINE_STATIC_KEY_TRUE_RO(name) \
    struct static_key_true name __ro_after_init = STATIC_KEY_TRUE_INIT
 
#define DECLARE_STATIC_KEY_TRUE(name)   \
    extern struct static_key_true name
 
#define DEFINE_STATIC_KEY_FALSE(name)   \
    struct static_key_false name = STATIC_KEY_FALSE_INIT
 
#define DEFINE_STATIC_KEY_FALSE_RO(name)    \
    struct static_key_false name __ro_after_init = STATIC_KEY_FALSE_INIT
 
#define DECLARE_STATIC_KEY_FALSE(name)  \
    extern struct static_key_false name
 
#define DEFINE_STATIC_KEY_ARRAY_TRUE(name, count)       \
    struct static_key_true name[count] = {          \
        [0 ... (count) - 1] = STATIC_KEY_TRUE_INIT, \
    }
 
#define DEFINE_STATIC_KEY_ARRAY_FALSE(name, count)      \
    struct static_key_false name[count] = {         \
        [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)                           \
({                                      \
    if (!__builtin_types_compatible_p(typeof(*x), struct static_key) && \
        !__builtin_types_compatible_p(typeof(*x), struct static_key_true) &&\
        !__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
        ____wrong_branch_error();                   \
    static_key_count((struct static_key *)x) > 0;               \
})
 
#ifdef CONFIG_JUMP_LABEL
 
/*
 * Combine the right initial value (type) with the right branch order
 * to generate the desired result.
 *
 *
 * type\branch| likely (1)        | unlikely (0)
 * -----------+-----------------------+------------------
 *            |                       |
 *  true (1)  |    ...            |    ...
 *            |    NOP            |    JMP L
 *            |    <br-stmts>         | 1: ...
 *            | L: ...            |
 *            |               |
 *            |               | L: <br-stmts>
 *            |               |    jmp 1b
 *            |                       |
 * -----------+-----------------------+------------------
 *            |                       |
 *  false (0) |    ...            |    ...
 *            |    JMP L          |    NOP
 *            |    <br-stmts>         | 1: ...
 *            | L: ...            |
 *            |               |
 *            |               | L: <br-stmts>
 *            |               |    jmp 1b
 *            |                       |
 * -----------+-----------------------+------------------
 *
 * The initial value is encoded in the LSB of static_key::entries,
 * type: 0 = false, 1 = true.
 *
 * The branch type is encoded in the LSB of jump_entry::key,
 * branch: 0 = unlikely, 1 = likely.
 *
 * This gives the following logic table:
 *
 *  enabled type    branch    instuction
 * -----------------------------+-----------
 *  0   0   0   | NOP
 *  0   0   1   | JMP
 *  0   1   0   | NOP
 *  0   1   1   | JMP
 *
 *  1   0   0   | JMP
 *  1   0   1   | NOP
 *  1   1   0   | JMP
 *  1   1   1   | NOP
 *
 * Which gives the following functions:
 *
 *   dynamic: instruction = enabled ^ branch
 *   static:  instruction = type ^ branch
 *
 * See jump_label_type() / jump_label_init_type().
 */
 
#define static_branch_likely(x)                         \
({                                      \
    bool branch;                                \
    if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
        branch = !arch_static_branch(&(x)->key, true);          \
    else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
        branch = !arch_static_branch_jump(&(x)->key, true);     \
    else                                    \
        branch = ____wrong_branch_error();              \
    likely_notrace(branch);                             \
})
 
#define static_branch_unlikely(x)                       \
({                                      \
    bool branch;                                \
    if (__builtin_types_compatible_p(typeof(*x), struct static_key_true))   \
        branch = arch_static_branch_jump(&(x)->key, false);     \
    else if (__builtin_types_compatible_p(typeof(*x), struct static_key_false)) \
        branch = arch_static_branch(&(x)->key, false);          \
    else                                    \
        branch = ____wrong_branch_error();              \
    unlikely_notrace(branch);                           \
})
 
#else /* !CONFIG_JUMP_LABEL */
 
#define static_branch_likely(x)     likely_notrace(static_key_enabled(&(x)->key))
#define static_branch_unlikely(x)   unlikely_notrace(static_key_enabled(&(x)->key))
 
#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
 */
 
#define static_branch_inc(x)        static_key_slow_inc(&(x)->key)
#define static_branch_dec(x)        static_key_slow_dec(&(x)->key)
#define static_branch_inc_cpuslocked(x) static_key_slow_inc_cpuslocked(&(x)->key)
#define static_branch_dec_cpuslocked(x) static_key_slow_dec_cpuslocked(&(x)->key)
 
/*
 * Normal usage; boolean enable/disable.
 */
 
#define static_branch_enable(x)         static_key_enable(&(x)->key)
#define static_branch_disable(x)        static_key_disable(&(x)->key)
#define static_branch_enable_cpuslocked(x)  static_key_enable_cpuslocked(&(x)->key)
#define static_branch_disable_cpuslocked(x) static_key_disable_cpuslocked(&(x)->key)
 
#endif /* __ASSEMBLY__ */
 
#endif  /* _LINUX_JUMP_LABEL_H */