[RFC][PATCH 6/7] jump_label: Add a new static_key interface

[Peter Zijlstra]

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 defines 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.

  XXX for archs that have variable width jmp encodings, please veryify
      the right sized jump is emitted.

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

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
 arch/arm/include/asm/jump_label.h     |   18 +++-
 arch/arm64/include/asm/jump_label.h   |   18 +++-
 arch/mips/include/asm/jump_label.h    |   19 ++++
 arch/powerpc/include/asm/jump_label.h |   19 ++++
 arch/s390/include/asm/jump_label.h    |   19 ++++
 arch/sparc/include/asm/jump_label.h   |   34 +++++---
 arch/x86/include/asm/jump_label.h     |   21 ++++
 include/linux/jump_label.h            |  143 ++++++++++++++++++++++++++++++++--
 kernel/jump_label.c                   |   27 +++++-
 9 files changed, 287 insertions(+), 31 deletions(-)

--- a/arch/arm/include/asm/jump_label.h
+++ b/arch/arm/include/asm/jump_label.h
@@ -13,14 +13,28 @@
 #define JUMP_LABEL_NOP	"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:\n\t"
 		 JUMP_LABEL_NOP "\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:
+	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"
+		 ".word 1b, %l[l_yes], %c0\n\t"
+		 ".popsection\n\t"
+		 : :  "i" (&((char *)key)[branch]) :  : l_yes);
 
 	return false;
 l_yes:
--- 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:
--- 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;
--- 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;
--- 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:	j %l[l_yes]\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;
--- a/arch/sparc/include/asm/jump_label.h
+++ b/arch/sparc/include/asm/jump_label.h
@@ -7,16 +7,32 @@
 
 #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"
+		 ".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;
--- 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_
 		_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;
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -107,12 +107,12 @@ static inline int static_key_count(struc
 
 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 s
 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 */
 
@@ -218,6 +218,137 @@ static inline void static_key_disable(st
 		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)		static_key_true(&(x)->key)
+#define static_branch_unlikely(x)	static_key_false(&(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__ */
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -165,16 +165,32 @@ static inline bool static_key_type(struc
 
 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 branch = jump_entry_branch(entry);
+
+	/* See the comment in linux/jump_label.h */
+	return enabled ^ branch;
+}
+
+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);
 
-	return enabled ^ type;
+	/* See the comment in linux/jump_label.h */
+	return type ^ branch;
 }
 
 static void __jump_label_update(struct static_key *key,
@@ -276,8 +292,11 @@ void jump_label_apply_nops(struct module
 	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)


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