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Commit 11276d53 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

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:

  a833581e ("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: default avatarPeter 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: default avatarIngo Molnar <mingo@kernel.org>
parent 706249c2

arch/arm/include/asm/jump_label.h

+17 −8
Original line number Diff line number Diff line
@@ -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:

arch/arm64/include/asm/jump_label.h

+16 −2
Original line number Diff line number Diff line
@@ -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:

arch/mips/include/asm/jump_label.h

+17 −2
Original line number Diff line number Diff line
@@ -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;

arch/powerpc/include/asm/jump_label.h

+17 −2
Original line number Diff line number Diff line
@@ -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;

arch/s390/include/asm/jump_label.h

+17 −2
Original line number Diff line number Diff line
@@ -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;