linux/arch/x86/include/asm/percpu.h

#ifndef ASM_X86__PERCPU_H
#define ASM_X86__PERCPU_H

#ifdef CONFIG_X86_64
#include <linux/compiler.h>

/* Same as asm-generic/percpu.h, except that we store the per cpu offset
   in the PDA. Longer term the PDA and every per cpu variable
   should be just put into a single section and referenced directly
   from %gs */

#ifdef CONFIG_SMP
#include <asm/pda.h>

#define __per_cpu_offset(cpu) (cpu_pda(cpu)->data_offset)
#define __my_cpu_offset read_pda(data_offset)

#define per_cpu_offset(x) (__per_cpu_offset(x))

#endif
#include <asm-generic/percpu.h>

DECLARE_PER_CPU(struct x8664_pda, pda);

/*
 * These are supposed to be implemented as a single instruction which
 * operates on the per-cpu data base segment.  x86-64 doesn't have
 * that yet, so this is a fairly inefficient workaround for the
 * meantime.  The single instruction is atomic with respect to
 * preemption and interrupts, so we need to explicitly disable
 * interrupts here to achieve the same effect.  However, because it
 * can be used from within interrupt-disable/enable, we can't actually
 * disable interrupts; disabling preemption is enough.
 */
#define x86_read_percpu(var)						\
	({								\
		typeof(per_cpu_var(var)) __tmp;				\
		preempt_disable();					\
		__tmp = __get_cpu_var(var);				\
		preempt_enable();					\
		__tmp;							\
	})

#define x86_write_percpu(var, val)					\
	do {								\
		preempt_disable();					\
		__get_cpu_var(var) = (val);				\
		preempt_enable();					\
	} while(0)

#else /* CONFIG_X86_64 */

#ifdef __ASSEMBLY__

/*
 * PER_CPU finds an address of a per-cpu variable.
 *
 * Args:
 *    var - variable name
 *    reg - 32bit register
 *
 * The resulting address is stored in the "reg" argument.
 *
 * Example:
 *    PER_CPU(cpu_gdt_descr, %ebx)
 */
#ifdef CONFIG_SMP
#define PER_CPU(var, reg)				\
	movl %fs:per_cpu__##this_cpu_off, reg;		\
	lea per_cpu__##var(reg), reg
#define PER_CPU_VAR(var)	%fs:per_cpu__##var
#else /* ! SMP */
#define PER_CPU(var, reg)			\
	movl $per_cpu__##var, reg
#define PER_CPU_VAR(var)	per_cpu__##var
#endif	/* SMP */

#else /* ...!ASSEMBLY */

/*
 * PER_CPU finds an address of a per-cpu variable.
 *
 * Args:
 *    var - variable name
 *    cpu - 32bit register containing the current CPU number
 *
 * The resulting address is stored in the "cpu" argument.
 *
 * Example:
 *    PER_CPU(cpu_gdt_descr, %ebx)
 */
#ifdef CONFIG_SMP

#define __my_cpu_offset x86_read_percpu(this_cpu_off)

/* fs segment starts at (positive) offset == __per_cpu_offset[cpu] */
#define __percpu_seg "%%fs:"

#else  /* !SMP */

#define __percpu_seg ""

#endif	/* SMP */

#include <asm-generic/percpu.h>

/* We can use this directly for local CPU (faster). */
DECLARE_PER_CPU(unsigned long, this_cpu_off);

/* For arch-specific code, we can use direct single-insn ops (they
 * don't give an lvalue though). */
extern void __bad_percpu_size(void);

#define percpu_to_op(op, var, val)			\
do {							\
	typedef typeof(var) T__;			\
	if (0) {					\
		T__ tmp__;				\
		tmp__ = (val);				\
	}						\
	switch (sizeof(var)) {				\
	case 1:						\
		asm(op "b %1,"__percpu_seg"%0"		\
		    : "+m" (var)			\
		    : "ri" ((T__)val));			\
		break;					\
	case 2:						\
		asm(op "w %1,"__percpu_seg"%0"		\
		    : "+m" (var)			\
		    : "ri" ((T__)val));			\
		break;					\
	case 4:						\
		asm(op "l %1,"__percpu_seg"%0"		\
		    : "+m" (var)			\
		    : "ri" ((T__)val));			\
		break;					\
	default: __bad_percpu_size();			\
	}						\
} while (0)

#define percpu_from_op(op, var)				\
({							\
	typeof(var) ret__;				\
	switch (sizeof(var)) {				\
	case 1:						\
		asm(op "b "__percpu_seg"%1,%0"		\
		    : "=r" (ret__)			\
		    : "m" (var));			\
		break;					\
	case 2:						\
		asm(op "w "__percpu_seg"%1,%0"		\
		    : "=r" (ret__)			\
		    : "m" (var));			\
		break;					\
	case 4:						\
		asm(op "l "__percpu_seg"%1,%0"		\
		    : "=r" (ret__)			\
		    : "m" (var));			\
		break;					\
	default: __bad_percpu_size();			\
	}						\
	ret__;						\
})

#define x86_read_percpu(var) percpu_from_op("mov", per_cpu__##var)
#define x86_write_percpu(var, val) percpu_to_op("mov", per_cpu__##var, val)
#define x86_add_percpu(var, val) percpu_to_op("add", per_cpu__##var, val)
#define x86_sub_percpu(var, val) percpu_to_op("sub", per_cpu__##var, val)
#define x86_or_percpu(var, val) percpu_to_op("or", per_cpu__##var, val)
#endif /* !__ASSEMBLY__ */
#endif /* !CONFIG_X86_64 */

#ifdef CONFIG_SMP

/*
 * Define the "EARLY_PER_CPU" macros.  These are used for some per_cpu
 * variables that are initialized and accessed before there are per_cpu
 * areas allocated.
 */

#define	DEFINE_EARLY_PER_CPU(_type, _name, _initvalue)			\
	DEFINE_PER_CPU(_type, _name) = _initvalue;			\
	__typeof__(_type) _name##_early_map[NR_CPUS] __initdata =	\
				{ [0 ... NR_CPUS-1] = _initvalue };	\
	__typeof__(_type) *_name##_early_ptr __refdata = _name##_early_map

#define EXPORT_EARLY_PER_CPU_SYMBOL(_name)			\
	EXPORT_PER_CPU_SYMBOL(_name)

#define DECLARE_EARLY_PER_CPU(_type, _name)			\
	DECLARE_PER_CPU(_type, _name);				\
	extern __typeof__(_type) *_name##_early_ptr;		\
	extern __typeof__(_type)  _name##_early_map[]

#define	early_per_cpu_ptr(_name) (_name##_early_ptr)
#define	early_per_cpu_map(_name, _idx) (_name##_early_map[_idx])
#define	early_per_cpu(_name, _cpu) 				\
	(early_per_cpu_ptr(_name) ?				\
		early_per_cpu_ptr(_name)[_cpu] :		\
		per_cpu(_name, _cpu))

#else	/* !CONFIG_SMP */
#define	DEFINE_EARLY_PER_CPU(_type, _name, _initvalue)		\
	DEFINE_PER_CPU(_type, _name) = _initvalue

#define EXPORT_EARLY_PER_CPU_SYMBOL(_name)			\
	EXPORT_PER_CPU_SYMBOL(_name)

#define DECLARE_EARLY_PER_CPU(_type, _name)			\
	DECLARE_PER_CPU(_type, _name)

#define	early_per_cpu(_name, _cpu) per_cpu(_name, _cpu)
#define	early_per_cpu_ptr(_name) NULL
/* no early_per_cpu_map() */

#endif	/* !CONFIG_SMP */

#endif /* ASM_X86__PERCPU_H */