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Date: Tue, 23 Dec 2008 12:15:05 -0500
From: Brian Gerst <brgerst@...il.com>
To: Ingo Molnar <mingo@...e.hu>
Cc: linux-kernel@...r.kernel.org, Brian Gerst <brgerst@...il.com>
Subject: [PATCH 2/3] x86-64: Unify x86_*_percpu() functions.
Merge the 32-bit and 64-bit versions of these functions. Unlike 32-bit,
the segment base is the current cpu's PDA instead of the offset from the
original per-cpu area. This is because GCC hardcodes the stackprotector
canary at %gs:40. Since the assembler is incapable of relocating against
multiple symbols, the code ends up looking like:
movq $per_cpu__var, reg
subq $per_cpu__pda, reg
movq %gs:(reg), reg
This is still atomic since the offset is a constant (just calculated at
runtime) and not dependant on the cpu number.
Signed-off-by: Brian Gerst <brgerst@...il.com>
---
arch/x86/include/asm/percpu.h | 92 +++++++++++++++++-----------------------
1 files changed, 39 insertions(+), 53 deletions(-)
diff --git a/arch/x86/include/asm/percpu.h b/arch/x86/include/asm/percpu.h
index 6f866fd..f704243 100644
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -1,54 +1,9 @@
#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 __my_cpu_offset read_pda(data_offset)
-
-#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__
+#ifdef CONFIG_X86_32
/*
* PER_CPU finds an address of a per-cpu variable.
*
@@ -72,6 +27,8 @@ DECLARE_PER_CPU(struct x8664_pda, pda);
#define PER_CPU_VAR(var) per_cpu__##var
#endif /* SMP */
+#endif /* X86_32 */
+
#else /* ...!ASSEMBLY */
/*
@@ -88,19 +45,37 @@ DECLARE_PER_CPU(struct x8664_pda, pda);
*/
#ifdef CONFIG_SMP
+#ifdef CONFIG_X86_32
+
#define __my_cpu_offset x86_read_percpu(this_cpu_off)
/* fs segment starts at (positive) offset == __per_cpu_offset[cpu] */
#define __percpu_seg "%%fs:"
+#define __percpu_seg_off(x) (x)
+
+#else
+
+#define __my_cpu_offset read_pda(data_offset)
+
+#define __percpu_seg "%%gs:"
+#define __percpu_seg_off(x) RELOC_HIDE((x), -(unsigned long)&per_cpu__pda)
+
+#endif
#else /* !SMP */
#define __percpu_seg ""
+#define __percpu_seg_off(x) (x)
#endif /* SMP */
#include <asm-generic/percpu.h>
+#ifdef CONFIG_X86_64
+#include <asm/pda.h>
+DECLARE_PER_CPU(struct x8664_pda, pda);
+#endif
+
/* We can use this directly for local CPU (faster). */
DECLARE_PER_CPU(unsigned long, this_cpu_off);
@@ -111,6 +86,7 @@ extern void __bad_percpu_size(void);
#define percpu_to_op(op, var, val) \
do { \
typedef typeof(var) T__; \
+ typeof(var) *var__ = __percpu_seg_off(&var); \
if (0) { \
T__ tmp__; \
tmp__ = (val); \
@@ -118,17 +94,22 @@ do { \
switch (sizeof(var)) { \
case 1: \
asm(op "b %1,"__percpu_seg"%0" \
- : "+m" (var) \
+ : "+m" (*var__) \
: "ri" ((T__)val)); \
break; \
case 2: \
asm(op "w %1,"__percpu_seg"%0" \
- : "+m" (var) \
+ : "+m" (*var__) \
: "ri" ((T__)val)); \
break; \
case 4: \
asm(op "l %1,"__percpu_seg"%0" \
- : "+m" (var) \
+ : "+m" (*var__) \
+ : "ri" ((T__)val)); \
+ break; \
+ case 8: \
+ asm(op "q %1,"__percpu_seg"%0" \
+ : "+m" (*var__) \
: "ri" ((T__)val)); \
break; \
default: __bad_percpu_size(); \
@@ -138,21 +119,27 @@ do { \
#define percpu_from_op(op, var) \
({ \
typeof(var) ret__; \
+ typeof(var) *var__ = __percpu_seg_off(&var); \
switch (sizeof(var)) { \
case 1: \
asm(op "b "__percpu_seg"%1,%0" \
: "=r" (ret__) \
- : "m" (var)); \
+ : "m" (*var__)); \
break; \
case 2: \
asm(op "w "__percpu_seg"%1,%0" \
: "=r" (ret__) \
- : "m" (var)); \
+ : "m" (*var__)); \
break; \
case 4: \
asm(op "l "__percpu_seg"%1,%0" \
: "=r" (ret__) \
- : "m" (var)); \
+ : "m" (*var__)); \
+ break; \
+ case 8: \
+ asm(op "q "__percpu_seg"%1,%0" \
+ : "=r" (ret__) \
+ : "m" (*var__)); \
break; \
default: __bad_percpu_size(); \
} \
@@ -165,7 +152,6 @@ do { \
#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
--
1.6.1.rc1
--
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