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Commit 9939ddaf authored by Tejun Heo's avatar Tejun Heo Committed by Ingo Molnar
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x86: merge 64 and 32 SMP percpu handling 



Now that pda is allocated as part of percpu, percpu doesn't need to be
accessed through pda.  Unify x86_64 SMP percpu access with x86_32 SMP
one.  Other than the segment register, operand size and the base of
percpu symbols, they behave identical now.

This patch replaces now unnecessary pda->data_offset with a dummy
field which is necessary to keep stack_canary at its place.  This
patch also moves per_cpu_offset initialization out of init_gdt() into
setup_per_cpu_areas().  Note that this change also necessitates
explicit per_cpu_offset initializations in voyager_smp.c.

With this change, x86_OP_percpu()'s are as efficient on x86_64 as on
x86_32 and also x86_64 can use assembly PER_CPU macros.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 1a51e3a0

arch/x86/include/asm/pda.h

+1 −2
Original line number Diff line number Diff line
@@ -11,8 +11,7 @@ 
/* Per processor datastructure. %gs points to it while the kernel runs */

struct x8664_pda {

	struct task_struct *pcurrent;	/* 0  Current process */

	unsigned long data_offset;	/* 8 Per cpu data offset from linker

					   address */

	unsigned long dummy;

	unsigned long kernelstack;	/* 16 top of kernel stack for current */

	unsigned long oldrsp;		/* 24 user rsp for system call */

	int irqcount;			/* 32 Irq nesting counter. Starts -1 */

arch/x86/include/asm/percpu.h

+39 −88
Original line number Diff line number Diff line 
#ifndef _ASM_X86_PERCPU_H

#define _ASM_X86_PERCPU_H



#ifndef __ASSEMBLY__

#ifdef CONFIG_X86_64

extern void load_pda_offset(int cpu);

#define __percpu_seg		gs

#define __percpu_mov_op		movq

#else

static inline void load_pda_offset(int cpu) { }

#endif

#endif



#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))



#define __percpu_seg		fs

#define __percpu_mov_op		movl

#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__
@@ -74,41 +25,25 @@ DECLARE_PER_CPU(struct x8664_pda, pda); 
 */

#ifdef CONFIG_SMP

#define PER_CPU(var, reg)						\

	movl %fs:per_cpu__##this_cpu_off, reg;		\

	__percpu_mov_op %__percpu_seg:per_cpu__this_cpu_off, reg;	\

	lea per_cpu__##var(reg), reg

#define PER_CPU_VAR(var)	%fs:per_cpu__##var

#define PER_CPU_VAR(var)	%__percpu_seg:per_cpu__##var

#else /* ! SMP */

#define PER_CPU(var, reg)						\

	movl $per_cpu__##var, reg

	__percpu_mov_op $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

#include <linux/stringify.h>



#ifdef CONFIG_SMP

#define __percpu_seg_str	"%%"__stringify(__percpu_seg)":"

#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 */

#else

#define __percpu_seg_str

#endif



#include <asm-generic/percpu.h>
@@ -128,20 +63,25 @@ do { \ 
	}						\

	switch (sizeof(var)) {				\

	case 1:						\

		asm(op "b %1,"__percpu_seg"%0"		\

		asm(op "b %1,"__percpu_seg_str"%0"	\

		    : "+m" (var)			\

		    : "ri" ((T__)val));			\

		break;					\

	case 2:						\

		asm(op "w %1,"__percpu_seg"%0"		\

		asm(op "w %1,"__percpu_seg_str"%0"	\

		    : "+m" (var)			\

		    : "ri" ((T__)val));			\

		break;					\

	case 4:						\

		asm(op "l %1,"__percpu_seg"%0"		\

		asm(op "l %1,"__percpu_seg_str"%0"	\

		    : "+m" (var)			\

		    : "ri" ((T__)val));			\

		break;					\

	case 8:						\

		asm(op "q %1,"__percpu_seg_str"%0"	\

		    : "+m" (var)			\

		    : "r" ((T__)val));			\

		break;					\

	default: __bad_percpu_size();			\

	}						\

} while (0)
@@ -151,17 +91,22 @@ do { \ 
	typeof(var) ret__;				\

	switch (sizeof(var)) {				\

	case 1:						\

		asm(op "b "__percpu_seg"%1,%0"		\

		asm(op "b "__percpu_seg_str"%1,%0"	\

		    : "=r" (ret__)			\

		    : "m" (var));			\

		break;					\

	case 2:						\

		asm(op "w "__percpu_seg"%1,%0"		\

		asm(op "w "__percpu_seg_str"%1,%0"	\

		    : "=r" (ret__)			\

		    : "m" (var));			\

		break;					\

	case 4:						\

		asm(op "l "__percpu_seg"%1,%0"		\

		asm(op "l "__percpu_seg_str"%1,%0"	\

		    : "=r" (ret__)			\

		    : "m" (var));			\

		break;					\

	case 8:						\

		asm(op "q "__percpu_seg_str"%1,%0"	\

		    : "=r" (ret__)			\

		    : "m" (var));			\

		break;					\
@@ -175,8 +120,14 @@ do { \ 
#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)



#ifdef CONFIG_X86_64

extern void load_pda_offset(int cpu);

#else

static inline void load_pda_offset(int cpu) { }

#endif



#endif /* !__ASSEMBLY__ */

#endif /* !CONFIG_X86_64 */



#ifdef CONFIG_SMP

arch/x86/kernel/asm-offsets_64.c

+0 −1
Original line number Diff line number Diff line
@@ -55,7 +55,6 @@ int main(void) 
	ENTRY(irqcount);

	ENTRY(cpunumber);

	ENTRY(irqstackptr);

	ENTRY(data_offset);

	DEFINE(pda_size, sizeof(struct x8664_pda));

	BLANK();

#undef ENTRY

arch/x86/kernel/entry_64.S

+4 −3
Original line number Diff line number Diff line
@@ -52,6 +52,7 @@ 
#include <asm/irqflags.h>

#include <asm/paravirt.h>

#include <asm/ftrace.h>

#include <asm/percpu.h>



/* Avoid __ASSEMBLER__'ifying <linux/audit.h> just for this.  */

#include <linux/elf-em.h>
@@ -1072,10 +1073,10 @@ ENTRY(\sym) 
	TRACE_IRQS_OFF

	movq %rsp,%rdi		/* pt_regs pointer */

	xorl %esi,%esi		/* no error code */

	movq %gs:pda_data_offset, %rbp

	subq $EXCEPTION_STKSZ, per_cpu__init_tss + TSS_ist + (\ist - 1) * 8(%rbp)

	PER_CPU(init_tss, %rbp)

	subq $EXCEPTION_STKSZ, TSS_ist + (\ist - 1) * 8(%rbp)

	call \do_sym

	addq $EXCEPTION_STKSZ, per_cpu__init_tss + TSS_ist + (\ist - 1) * 8(%rbp)

	addq $EXCEPTION_STKSZ, TSS_ist + (\ist - 1) * 8(%rbp)

	jmp paranoid_exit	/* %ebx: no swapgs flag */

	CFI_ENDPROC

END(\sym)

arch/x86/kernel/head64.c

+0 −2
Original line number Diff line number Diff line
@@ -38,8 +38,6 @@ void __init x86_64_init_pda(void) 
#else

	cpu_pda(0) = &_boot_cpu_pda;

#endif

	cpu_pda(0)->data_offset =

		(unsigned long)(__per_cpu_load - __per_cpu_start);

	pda_init(0);

}