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Subject[PATCH 09/13] x86_64: merge 64 and 32 SMP percpu handling
Date
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: Tejun Heo <tj@kernel.org>
Cc: Mike Travis <travis@sgi.com>
---
arch/x86/include/asm/pda.h | 3 +-
arch/x86/include/asm/percpu.h | 127 +++++++++++------------------------
arch/x86/kernel/asm-offsets_64.c | 1 -
arch/x86/kernel/entry_64.S | 7 +-
arch/x86/kernel/head64.c | 2 -
arch/x86/kernel/setup_percpu.c | 15 ++--
arch/x86/kernel/smpcommon.c | 3 +-
arch/x86/mach-voyager/voyager_smp.c | 2 +
8 files changed, 55 insertions(+), 105 deletions(-)
diff --git a/arch/x86/include/asm/pda.h b/arch/x86/include/asm/pda.h
index 2d5b49c..e91558e 100644
--- a/arch/x86/include/asm/pda.h
+++ b/arch/x86/include/asm/pda.h
@@ -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 */
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 0ed77cf..556f84b 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -1,62 +1,13 @@
#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__

@@ -73,42 +24,26 @@ DECLARE_PER_CPU(struct x8664_pda, pda);
* PER_CPU(cpu_gdt_descr, %ebx)
*/
#ifdef CONFIG_SMP
-#define PER_CPU(var, reg) \
- movl %fs:per_cpu__##this_cpu_off, reg; \
+#define PER_CPU(var, 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
+#define 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
-
-#define __my_cpu_offset x86_read_percpu(this_cpu_off)
-
-/* fs segment starts at (positive) offset == __per_cpu_offset[cpu] */
-#define __percpu_seg "%%fs:"
+#include <linux/stringify.h>

-#else /* !SMP */
-
-#define __percpu_seg ""
-
-#endif /* SMP */
+#ifdef CONFIG_SMP
+#define __percpu_seg_str "%%"__stringify(__percpu_seg)":"
+#define __my_cpu_offset x86_read_percpu(this_cpu_off)
+#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

diff --git a/arch/x86/kernel/asm-offsets_64.c b/arch/x86/kernel/asm-offsets_64.c
index f8d1b04..f4cc81b 100644
--- a/arch/x86/kernel/asm-offsets_64.c
+++ b/arch/x86/kernel/asm-offsets_64.c
@@ -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
diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index e28c7a9..4833f3a 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -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)
diff --git a/arch/x86/kernel/head64.c b/arch/x86/kernel/head64.c
index ff39bdd..9194074 100644
--- a/arch/x86/kernel/head64.c
+++ b/arch/x86/kernel/head64.c
@@ -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);
}

diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 24d3e0d..76a2498 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -105,14 +105,14 @@ static void __init setup_per_cpu_maps(void)
#endif
}

-#ifdef CONFIG_X86_32
-/*
- * Great future not-so-futuristic plan: make i386 and x86_64 do it
- * the same way
- */
+#ifdef CONFIG_X86_64
+unsigned long __per_cpu_offset[NR_CPUS] __read_mostly = {
+ [0] = (unsigned long)__per_cpu_load,
+};
+#else
unsigned long __per_cpu_offset[NR_CPUS] __read_mostly;
-EXPORT_SYMBOL(__per_cpu_offset);
#endif
+EXPORT_SYMBOL(__per_cpu_offset);

/*
* Great future plan:
@@ -159,6 +159,7 @@ void __init setup_per_cpu_areas(void)
#endif

memcpy(ptr, __per_cpu_load, __per_cpu_end - __per_cpu_start);
+ per_cpu_offset(cpu) = ptr - __per_cpu_start;
#ifdef CONFIG_X86_64
cpu_pda(cpu) = (void *)ptr;

@@ -171,7 +172,7 @@ void __init setup_per_cpu_areas(void)
else
memset(cpu_pda(cpu), 0, sizeof(*cpu_pda(cpu)));
#endif
- per_cpu_offset(cpu) = ptr - __per_cpu_start;
+ per_cpu(this_cpu_off, cpu) = per_cpu_offset(cpu);

DBG("PERCPU: cpu %4d %p\n", cpu, ptr);
}
diff --git a/arch/x86/kernel/smpcommon.c b/arch/x86/kernel/smpcommon.c
index 397e309..84395fa 100644
--- a/arch/x86/kernel/smpcommon.c
+++ b/arch/x86/kernel/smpcommon.c
@@ -4,10 +4,10 @@
#include <linux/module.h>
#include <asm/smp.h>

-#ifdef CONFIG_X86_32
DEFINE_PER_CPU(unsigned long, this_cpu_off);
EXPORT_PER_CPU_SYMBOL(this_cpu_off);

+#ifdef CONFIG_X86_32
/*
* Initialize the CPU's GDT. This is either the boot CPU doing itself
* (still using the master per-cpu area), or a CPU doing it for a
@@ -24,7 +24,6 @@ __cpuinit void init_gdt(int cpu)
write_gdt_entry(get_cpu_gdt_table(cpu),
GDT_ENTRY_PERCPU, &gdt, DESCTYPE_S);

- per_cpu(this_cpu_off, cpu) = __per_cpu_offset[cpu];
per_cpu(cpu_number, cpu) = cpu;
}
#endif
diff --git a/arch/x86/mach-voyager/voyager_smp.c b/arch/x86/mach-voyager/voyager_smp.c
index 5214500..7d79a52 100644
--- a/arch/x86/mach-voyager/voyager_smp.c
+++ b/arch/x86/mach-voyager/voyager_smp.c
@@ -539,6 +539,7 @@ static void __init do_boot_cpu(__u8 cpu)
stack_start.sp = (void *)idle->thread.sp;

init_gdt(cpu);
+ per_cpu(this_cpu_off, cpu) = __per_cpu_offset[cpu];
per_cpu(current_task, cpu) = idle;
early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
irq_ctx_init(cpu);
@@ -1756,6 +1757,7 @@ static void __init voyager_smp_prepare_cpus(unsigned int max_cpus)
static void __cpuinit voyager_smp_prepare_boot_cpu(void)
{
init_gdt(smp_processor_id());
+ per_cpu(this_cpu_off, cpu) = __per_cpu_offset[cpu];
switch_to_new_gdt();

cpu_set(smp_processor_id(), cpu_online_map);
--
1.5.6


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