locking/static_keys: Add a new static_key interface

There are various problems and short-comings with the current
static_key interface:

 - static_key_{true,false}() read like a branch depending on the key
   value, instead of the actual likely/unlikely branch depending on
   init value.

 - static_key_{true,false}() are, as stated above, tied to the
   static_key init values STATIC_KEY_INIT_{TRUE,FALSE}.

 - we're limited to the 2 (out of 4) possible options that compile to
   a default NOP because that's what our arch_static_branch() assembly
   emits.

So provide a new static_key interface:

  DEFINE_STATIC_KEY_TRUE(name);
  DEFINE_STATIC_KEY_FALSE(name);

Which define a key of different types with an initial true/false
value.

Then allow:

   static_branch_likely()
   static_branch_unlikely()

to take a key of either type and emit the right instruction for the
case.

This means adding a second arch_static_branch_jump() assembly helper
which emits a JMP per default.

In order to determine the right instruction for the right state,
encode the branch type in the LSB of jump_entry::key.

This is the final step in removing the naming confusion that has led to
a stream of avoidable bugs such as:

  a833581e372a ("x86, perf: Fix static_key bug in load_mm_cr4()")

... but it also allows new static key combinations that will give us
performance enhancements in the subsequent patches.

Tested-by: Rabin Vincent <rabin@rab.in> # arm
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> # ppc
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com> # s390
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

9 files changed, 298 insertions, 44 deletions

diff --git a/arch/arm/include/asm/jump_label.h b/arch/arm/include/asm/jump_label.h
index 5f337dc5c108..34f7b6980d21 100644
--- a/arch/arm/include/asm/jump_label.h
+++ b/arch/arm/include/asm/jump_label.h
@@ -4,23 +4,32 @@
 #ifndef __ASSEMBLY__
 
 #include <linux/types.h>
+#include <asm/unified.h>
 
 #define JUMP_LABEL_NOP_SIZE 4
 
-#ifdef CONFIG_THUMB2_KERNEL
-#define JUMP_LABEL_NOP  "nop.w"
-#else
-#define JUMP_LABEL_NOP  "nop"
-#endif
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
+{
+        asm_volatile_goto("1:\n\t"
+                 WASM(nop) "\n\t"
+                 ".pushsection __jump_table,  \"aw\"\n\t"
+                 ".word 1b, %l[l_yes], %c0\n\t"
+                 ".popsection\n\t"
+                 : :  "i" (&((char *)key)[branch]) :  : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
 
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
 {
         asm_volatile_goto("1:\n\t"
-                 JUMP_LABEL_NOP "\n\t"
+                 WASM(b) " %l[l_yes]\n\t"
                  ".pushsection __jump_table,  \"aw\"\n\t"
                  ".word 1b, %l[l_yes], %c0\n\t"
                  ".popsection\n\t"
-                 : :  "i" (key) :  : l_yes);
+                 : :  "i" (&((char *)key)[branch]) :  : l_yes);
 
         return false;
 l_yes:
diff --git a/arch/arm64/include/asm/jump_label.h b/arch/arm64/include/asm/jump_label.h
index c0e5165c2f76..1b5e0e843c3a 100644
--- a/arch/arm64/include/asm/jump_label.h
+++ b/arch/arm64/include/asm/jump_label.h
@@ -26,14 +26,28 @@
 
 #define JUMP_LABEL_NOP_SIZE             AARCH64_INSN_SIZE
 
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
         asm goto("1: nop\n\t"
                  ".pushsection __jump_table,  \"aw\"\n\t"
                  ".align 3\n\t"
                  ".quad 1b, %l[l_yes], %c0\n\t"
                  ".popsection\n\t"
-                 :  :  "i"(key) :  : l_yes);
+                 :  :  "i"(&((char *)key)[branch]) :  : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+        asm goto("1: b %l[l_yes]\n\t"
+                 ".pushsection __jump_table,  \"aw\"\n\t"
+                 ".align 3\n\t"
+                 ".quad 1b, %l[l_yes], %c0\n\t"
+                 ".popsection\n\t"
+                 :  :  "i"(&((char *)key)[branch]) :  : l_yes);
 
         return false;
 l_yes:
diff --git a/arch/mips/include/asm/jump_label.h b/arch/mips/include/asm/jump_label.h
index 608aa57799c8..e77672539e8e 100644
--- a/arch/mips/include/asm/jump_label.h
+++ b/arch/mips/include/asm/jump_label.h
@@ -26,14 +26,29 @@
 #define NOP_INSN "nop"
 #endif
 
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
         asm_volatile_goto("1:\t" NOP_INSN "\n\t"
                 "nop\n\t"
                 ".pushsection __jump_table,  \"aw\"\n\t"
                 WORD_INSN " 1b, %l[l_yes], %0\n\t"
                 ".popsection\n\t"
-                : :  "i" (key) : : l_yes);
+                : :  "i" (&((char *)key)[branch]) : : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+        asm_volatile_goto("1:\tj %l[l_yes]\n\t"
+                "nop\n\t"
+                ".pushsection __jump_table,  \"aw\"\n\t"
+                WORD_INSN " 1b, %l[l_yes], %0\n\t"
+                ".popsection\n\t"
+                : :  "i" (&((char *)key)[branch]) : : l_yes);
+
         return false;
 l_yes:
         return true;
diff --git a/arch/powerpc/include/asm/jump_label.h b/arch/powerpc/include/asm/jump_label.h
index efbf9a322a23..47e155f15433 100644
--- a/arch/powerpc/include/asm/jump_label.h
+++ b/arch/powerpc/include/asm/jump_label.h
@@ -18,14 +18,29 @@
 #define JUMP_ENTRY_TYPE         stringify_in_c(FTR_ENTRY_LONG)
 #define JUMP_LABEL_NOP_SIZE     4
 
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
         asm_volatile_goto("1:\n\t"
                  "nop\n\t"
                  ".pushsection __jump_table,  \"aw\"\n\t"
                  JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
                  ".popsection \n\t"
-                 : :  "i" (key) : : l_yes);
+                 : :  "i" (&((char *)key)[branch]) : : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+        asm_volatile_goto("1:\n\t"
+                 "b %l[l_yes]\n\t"
+                 ".pushsection __jump_table,  \"aw\"\n\t"
+                 JUMP_ENTRY_TYPE "1b, %l[l_yes], %c0\n\t"
+                 ".popsection \n\t"
+                 : :  "i" (&((char *)key)[branch]) : : l_yes);
+
         return false;
 l_yes:
         return true;
diff --git a/arch/s390/include/asm/jump_label.h b/arch/s390/include/asm/jump_label.h
index 69972b7957ee..7f9fd5e3f1bf 100644
--- a/arch/s390/include/asm/jump_label.h
+++ b/arch/s390/include/asm/jump_label.h
@@ -12,14 +12,29 @@
  * We use a brcl 0,2 instruction for jump labels at compile time so it
  * can be easily distinguished from a hotpatch generated instruction.
  */
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
         asm_volatile_goto("0:   brcl 0,"__stringify(JUMP_LABEL_NOP_OFFSET)"\n"
                 ".pushsection __jump_table, \"aw\"\n"
                 ".balign 8\n"
                 ".quad 0b, %l[label], %0\n"
                 ".popsection\n"
-                : : "X" (key) : : label);
+                : : "X" (&((char *)key)[branch]) : : label);
+
+        return false;
+label:
+        return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+        asm_volatile_goto("0:   brcl 15, %l[label]\n"
+                ".pushsection __jump_table, \"aw\"\n"
+                ".balign 8\n"
+                ".quad 0b, %l[label], %0\n"
+                ".popsection\n"
+                : : "X" (&((char *)key)[branch]) : : label);
+
         return false;
 label:
         return true;
diff --git a/arch/sparc/include/asm/jump_label.h b/arch/sparc/include/asm/jump_label.h
index cc9b04a2b11b..62d0354d1727 100644
--- a/arch/sparc/include/asm/jump_label.h
+++ b/arch/sparc/include/asm/jump_label.h
@@ -7,16 +7,33 @@
 
 #define JUMP_LABEL_NOP_SIZE 4
 
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
-                asm_volatile_goto("1:\n\t"
-                         "nop\n\t"
-                         "nop\n\t"
-                         ".pushsection __jump_table,  \"aw\"\n\t"
-                         ".align 4\n\t"
-                         ".word 1b, %l[l_yes], %c0\n\t"
-                         ".popsection \n\t"
-                         : :  "i" (key) : : l_yes);
+        asm_volatile_goto("1:\n\t"
+                 "nop\n\t"
+                 "nop\n\t"
+                 ".pushsection __jump_table,  \"aw\"\n\t"
+                 ".align 4\n\t"
+                 ".word 1b, %l[l_yes], %c0\n\t"
+                 ".popsection \n\t"
+                 : :  "i" (&((char *)key)[branch]) : : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+        asm_volatile_goto("1:\n\t"
+                 "b %l[l_yes]\n\t"
+                 "nop\n\t"
+                 ".pushsection __jump_table,  \"aw\"\n\t"
+                 ".align 4\n\t"
+                 ".word 1b, %l[l_yes], %c0\n\t"
+                 ".popsection \n\t"
+                 : :  "i" (&((char *)key)[branch]) : : l_yes);
+
         return false;
 l_yes:
         return true;
diff --git a/arch/x86/include/asm/jump_label.h b/arch/x86/include/asm/jump_label.h
index a4c1cf7e93f8..28d7a857f9d1 100644
--- a/arch/x86/include/asm/jump_label.h
+++ b/arch/x86/include/asm/jump_label.h
@@ -16,7 +16,7 @@
 # define STATIC_KEY_INIT_NOP GENERIC_NOP5_ATOMIC
 #endif
 
-static __always_inline bool arch_static_branch(struct static_key *key)
+static __always_inline bool arch_static_branch(struct static_key *key, bool branch)
 {
         asm_volatile_goto("1:"
                 ".byte " __stringify(STATIC_KEY_INIT_NOP) "\n\t"
@@ -24,7 +24,24 @@ static __always_inline bool arch_static_branch(struct static_key *key)
                 _ASM_ALIGN "\n\t"
                 _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
                 ".popsection \n\t"
-                : :  "i" (key) : : l_yes);
+                : :  "i" (&((char *)key)[branch]) : : l_yes);
+
+        return false;
+l_yes:
+        return true;
+}
+
+static __always_inline bool arch_static_branch_jump(struct static_key *key, bool branch)
+{
+        asm_volatile_goto("1:"
+                ".byte 0xe9\n\t .long %l[l_yes] - 2f\n\t"
+                "2:\n\t"
+                ".pushsection __jump_table,  \"aw\" \n\t"
+                _ASM_ALIGN "\n\t"
+                _ASM_PTR "1b, %l[l_yes], %c0 \n\t"
+                ".popsection \n\t"
+                : :  "i" (&((char *)key)[branch]) : : l_yes);
+
         return false;
 l_yes:
         return true;
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 65f0ebac63cf..e337a1961933 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -107,12 +107,12 @@ static inline int static_key_count(struct static_key *key)
 
 static __always_inline bool static_key_false(struct static_key *key)
 {
-        return arch_static_branch(key);
+        return arch_static_branch(key, false);
 }
 
 static __always_inline bool static_key_true(struct static_key *key)
 {
-        return !static_key_false(key);
+        return !arch_static_branch(key, true);
 }
 
 extern struct jump_entry __start___jump_table[];
@@ -130,12 +130,12 @@ 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)               \
+#define STATIC_KEY_INIT_TRUE                                    \
         { .enabled = ATOMIC_INIT(1),                            \
-          .entries = (void *)JUMP_TYPE_TRUE })
-#define STATIC_KEY_INIT_FALSE ((struct static_key)              \
+          .entries = (void *)JUMP_TYPE_TRUE }
+#define STATIC_KEY_INIT_FALSE                                   \
         { .enabled = ATOMIC_INIT(0),                            \
-          .entries = (void *)JUMP_TYPE_FALSE })
+          .entries = (void *)JUMP_TYPE_FALSE }
 
 #else  /* !HAVE_JUMP_LABEL */
 
@@ -183,10 +183,8 @@ 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) })
+#define STATIC_KEY_INIT_TRUE    { .enabled = ATOMIC_INIT(1) }
+#define STATIC_KEY_INIT_FALSE   { .enabled = ATOMIC_INIT(0) }
 
 #endif  /* HAVE_JUMP_LABEL */
 
@@ -218,6 +216,137 @@ static inline void static_key_disable(struct static_key *key)
                 static_key_slow_dec(key);
 }
 
+/* -------------------------------------------------------------------------- */
+
+/*
+ * 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_FALSE(name)   \
+        struct static_key_false name = STATIC_KEY_FALSE_INIT
+
+#ifdef HAVE_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().
+ */
+
+extern bool ____wrong_branch_error(void);
+
+#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();                              \
+        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();                              \
+        branch;                                                                 \
+})
+
+#else /* !HAVE_JUMP_LABEL */
+
+#define static_branch_likely(x)         likely(static_key_enabled(&(x)->key))
+#define static_branch_unlikely(x)       unlikely(static_key_enabled(&(x)->key))
+
+#endif /* HAVE_JUMP_LABEL */
+
+/*
+ * 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)
+
+/*
+ * 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)
+
 #endif  /* _LINUX_JUMP_LABEL_H */
 
 #endif /* __ASSEMBLY__ */
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 2e7cc1e4b4b5..8fd00d892286 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -165,16 +165,22 @@ static inline bool static_key_type(struct static_key *key)
 
 static inline struct static_key *jump_entry_key(struct jump_entry *entry)
 {
-        return (struct static_key *)((unsigned long)entry->key);
+        return (struct static_key *)((unsigned long)entry->key & ~1UL);
+}
+
+static bool jump_entry_branch(struct jump_entry *entry)
+{
+        return (unsigned long)entry->key & 1UL;
 }
 
 static enum jump_label_type jump_label_type(struct jump_entry *entry)
 {
         struct static_key *key = jump_entry_key(entry);
         bool enabled = static_key_enabled(key);
-        bool type = static_key_type(key);
+        bool branch = jump_entry_branch(entry);
 
-        return enabled ^ type;
+        /* See the comment in linux/jump_label.h */
+        return enabled ^ branch;
 }
 
 static void __jump_label_update(struct static_key *key,
@@ -205,7 +211,10 @@ void __init jump_label_init(void)
         for (iter = iter_start; iter < iter_stop; iter++) {
                 struct static_key *iterk;
 
-                arch_jump_label_transform_static(iter, jump_label_type(iter));
+                /* rewrite NOPs */
+                if (jump_label_type(iter) == JUMP_LABEL_NOP)
+                        arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
+
                 iterk = jump_entry_key(iter);
                 if (iterk == key)
                         continue;
@@ -225,6 +234,16 @@ void __init jump_label_init(void)
 
 #ifdef CONFIG_MODULES
 
+static enum jump_label_type jump_label_init_type(struct jump_entry *entry)
+{
+        struct static_key *key = jump_entry_key(entry);
+        bool type = static_key_type(key);
+        bool branch = jump_entry_branch(entry);
+
+        /* See the comment in linux/jump_label.h */
+        return type ^ branch;
+}
+
 struct static_key_mod {
         struct static_key_mod *next;
         struct jump_entry *entries;
@@ -276,8 +295,11 @@ void jump_label_apply_nops(struct module *mod)
         if (iter_start == iter_stop)
                 return;
 
-        for (iter = iter_start; iter < iter_stop; iter++)
-                arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
+        for (iter = iter_start; iter < iter_stop; iter++) {
+                /* Only write NOPs for arch_branch_static(). */
+                if (jump_label_init_type(iter) == JUMP_LABEL_NOP)
+                        arch_jump_label_transform_static(iter, JUMP_LABEL_NOP);
+        }
 }
 
 static int jump_label_add_module(struct module *mod)
@@ -318,7 +340,8 @@ static int jump_label_add_module(struct module *mod)
                 jlm->next = key->next;
                 key->next = jlm;
 
-                if (jump_label_type(iter) == JUMP_LABEL_JMP)
+                /* Only update if we've changed from our initial state */
+                if (jump_label_type(iter) != jump_label_init_type(iter))
                         __jump_label_update(key, iter, iter_stop);
         }