3.16.68-rc1 review patch. If anyone has any objections, please let me know.
------------------
From: Peter Zijlstra peterz@infradead.org
commit 11276d5306b8e5b438a36bbff855fe792d7eaa61 upstream.
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 [bwh: Backported to 3.16: - For s390, use the 31-bit-compatible macros in arch_static_branch_jump() - Signed-off-by: Ben Hutchings ben@decadent.org.uk --- arch/arm/include/asm/jump_label.h | 25 +++-- 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 | 35 ++++-- arch/x86/include/asm/jump_label.h | 21 +++- include/linux/jump_label.h | 149 ++++++++++++++++++++++++-- kernel/jump_label.c | 37 +++++-- 9 files changed, 298 insertions(+), 44 deletions(-)
--- 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: --- 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 @@ -17,14 +17,29 @@ #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 @@ -20,14 +20,29 @@ * 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" ASM_ALIGN "\n" ASM_PTR " 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" + ASM_ALIGN "\n" + ASM_PTR " 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 +7,33 @@
#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; --- 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 */
@@ -183,10 +183,8 @@ static inline int jump_label_apply_nops( 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(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) 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__ */ --- a/kernel/jump_label.c +++ b/kernel/jump_label.c @@ -172,16 +172,22 @@ 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 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, @@ -212,7 +218,10 @@ 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; @@ -232,6 +241,16 @@ 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; @@ -283,8 +302,11 @@ 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) @@ -325,7 +347,8 @@ static int jump_label_add_module(struct 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); }