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arm64: introduce CONFIG_ARM64_LSE_ATOMICS as fallback to ll/sc atomics 

In order to patch in the new atomic instructions at runtime, we need to
generate wrappers around the out-of-line exclusive load/store atomics.

This patch adds a new Kconfig option, CONFIG_ARM64_LSE_ATOMICS. which
causes our atomic functions to branch to the out-of-line ll/sc
implementations. To avoid the register spill overhead of the PCS, the
out-of-line functions are compiled with specific compiler flags to
force out-of-line save/restore of any registers that are usually
caller-saved.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
This commit is contained in:
Will Deacon 2015-02-03 12:39:03 +00:00
parent d964b7229e
commit c0385b24af
6 changed files with 224 additions and 2 deletions
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12
arch/arm64/Kconfig
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@ -618,6 +618,18 @@ config ARM64_PAN
The feature is detected at runtime, and will remain as a 'nop'
instruction if the cpu does not implement the feature.
config ARM64_LSE_ATOMICS
bool "ARMv8.1 atomic instructions"
help
As part of the Large System Extensions, ARMv8.1 introduces new
atomic instructions that are designed specifically to scale in
very large systems.
Say Y here to make use of these instructions for the in-kernel
atomic routines. This incurs a small overhead on CPUs that do
not support these instructions and requires the kernel to be
built with binutils >= 2.25.
menuconfig ARMV8_DEPRECATED
bool "Emulate deprecated/obsolete ARMv8 instructions"
depends on COMPAT

9
arch/arm64/include/asm/atomic.h
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@ -21,6 +21,7 @@
#define __ASM_ATOMIC_H
#include <linux/compiler.h>
#include <linux/stringify.h>
#include <linux/types.h>
#include <asm/barrier.h>
@ -30,7 +31,15 @@
#ifdef __KERNEL__
#define __ARM64_IN_ATOMIC_IMPL
#ifdef CONFIG_ARM64_LSE_ATOMICS
#include <asm/atomic_lse.h>
#else
#include <asm/atomic_ll_sc.h>
#endif
#undef __ARM64_IN_ATOMIC_IMPL
/*
* On ARM, ordinary assignment (str instruction) doesn't clear the local

19
arch/arm64/include/asm/atomic_ll_sc.h
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@ -21,6 +21,10 @@
#ifndef __ASM_ATOMIC_LL_SC_H
#define __ASM_ATOMIC_LL_SC_H
#ifndef __ARM64_IN_ATOMIC_IMPL
#error "please don't include this file directly"
#endif
/*
* AArch64 UP and SMP safe atomic ops. We use load exclusive and
* store exclusive to ensure that these are atomic. We may loop
@ -41,6 +45,10 @@
#define __LL_SC_PREFIX(x) x
#endif
#ifndef __LL_SC_EXPORT
#define __LL_SC_EXPORT(x)
#endif
#define ATOMIC_OP(op, asm_op) \
__LL_SC_INLINE void \
__LL_SC_PREFIX(atomic_##op(int i, atomic_t *v)) \
@ -56,6 +64,7 @@ __LL_SC_PREFIX(atomic_##op(int i, atomic_t *v)) \
: "=&r" (result), "=&r" (tmp), "+Q" (v->counter) \
: "Ir" (i)); \
} \
__LL_SC_EXPORT(atomic_##op);
#define ATOMIC_OP_RETURN(op, asm_op) \
__LL_SC_INLINE int \
@ -75,7 +84,8 @@ __LL_SC_PREFIX(atomic_##op##_return(int i, atomic_t *v)) \
\
smp_mb(); \
return result; \
}
} \
__LL_SC_EXPORT(atomic_##op##_return);
#define ATOMIC_OPS(op, asm_op) \
ATOMIC_OP(op, asm_op) \
@ -115,6 +125,7 @@ __LL_SC_PREFIX(atomic_cmpxchg(atomic_t *ptr, int old, int new))
smp_mb();
return oldval;
}
__LL_SC_EXPORT(atomic_cmpxchg);
#define ATOMIC64_OP(op, asm_op) \
__LL_SC_INLINE void \
@ -131,6 +142,7 @@ __LL_SC_PREFIX(atomic64_##op(long i, atomic64_t *v)) \
: "=&r" (result), "=&r" (tmp), "+Q" (v->counter) \
: "Ir" (i)); \
} \
__LL_SC_EXPORT(atomic64_##op);
#define ATOMIC64_OP_RETURN(op, asm_op) \
__LL_SC_INLINE long \
@ -150,7 +162,8 @@ __LL_SC_PREFIX(atomic64_##op##_return(long i, atomic64_t *v)) \
\
smp_mb(); \
return result; \
}
} \
__LL_SC_EXPORT(atomic64_##op##_return);
#define ATOMIC64_OPS(op, asm_op) \
ATOMIC64_OP(op, asm_op) \
@ -190,6 +203,7 @@ __LL_SC_PREFIX(atomic64_cmpxchg(atomic64_t *ptr, long old, long new))
smp_mb();
return oldval;
}
__LL_SC_EXPORT(atomic64_cmpxchg);
__LL_SC_INLINE long
__LL_SC_PREFIX(atomic64_dec_if_positive(atomic64_t *v))
@ -211,5 +225,6 @@ __LL_SC_PREFIX(atomic64_dec_if_positive(atomic64_t *v))
return result;
}
__LL_SC_EXPORT(atomic64_dec_if_positive);
#endif /* __ASM_ATOMIC_LL_SC_H */

170
arch/arm64/include/asm/atomic_lse.h Normal file
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@ -0,0 +1,170 @@
/*
* Based on arch/arm/include/asm/atomic.h
*
* Copyright (C) 1996 Russell King.
* Copyright (C) 2002 Deep Blue Solutions Ltd.
* Copyright (C) 2012 ARM Ltd.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#ifndef __ASM_ATOMIC_LSE_H
#define __ASM_ATOMIC_LSE_H
#ifndef __ARM64_IN_ATOMIC_IMPL
#error "please don't include this file directly"
#endif
/* Move the ll/sc atomics out-of-line */
#define __LL_SC_INLINE
#define __LL_SC_PREFIX(x) __ll_sc_##x
#define __LL_SC_EXPORT(x) EXPORT_SYMBOL(__LL_SC_PREFIX(x))
/* Macros for constructing calls to out-of-line ll/sc atomics */
#define __LL_SC_CALL(op) \
"bl\t" __stringify(__LL_SC_PREFIX(atomic_##op)) "\n"
#define __LL_SC_CALL64(op) \
"bl\t" __stringify(__LL_SC_PREFIX(atomic64_##op)) "\n"
#define ATOMIC_OP(op, asm_op) \
static inline void atomic_##op(int i, atomic_t *v) \
{ \
register int w0 asm ("w0") = i; \
register atomic_t *x1 asm ("x1") = v; \
\
asm volatile( \
__LL_SC_CALL(op) \
: "+r" (w0), "+Q" (v->counter) \
: "r" (x1) \
: "x30"); \
} \
#define ATOMIC_OP_RETURN(op, asm_op) \
static inline int atomic_##op##_return(int i, atomic_t *v) \
{ \
register int w0 asm ("w0") = i; \
register atomic_t *x1 asm ("x1") = v; \
\
asm volatile( \
__LL_SC_CALL(op##_return) \
: "+r" (w0) \
: "r" (x1) \
: "x30", "memory"); \
\
return w0; \
}
#define ATOMIC_OPS(op, asm_op) \
ATOMIC_OP(op, asm_op) \
ATOMIC_OP_RETURN(op, asm_op)
ATOMIC_OPS(add, add)
ATOMIC_OPS(sub, sub)
ATOMIC_OP(and, and)
ATOMIC_OP(andnot, bic)
ATOMIC_OP(or, orr)
ATOMIC_OP(xor, eor)
#undef ATOMIC_OPS
#undef ATOMIC_OP_RETURN
#undef ATOMIC_OP
static inline int atomic_cmpxchg(atomic_t *ptr, int old, int new)
{
register unsigned long x0 asm ("x0") = (unsigned long)ptr;
register int w1 asm ("w1") = old;
register int w2 asm ("w2") = new;
asm volatile(
__LL_SC_CALL(cmpxchg)
: "+r" (x0)
: "r" (w1), "r" (w2)
: "x30", "cc", "memory");
return x0;
}
#define ATOMIC64_OP(op, asm_op) \
static inline void atomic64_##op(long i, atomic64_t *v) \
{ \
register long x0 asm ("x0") = i; \
register atomic64_t *x1 asm ("x1") = v; \
\
asm volatile( \
__LL_SC_CALL64(op) \
: "+r" (x0), "+Q" (v->counter) \
: "r" (x1) \
: "x30"); \
} \
#define ATOMIC64_OP_RETURN(op, asm_op) \
static inline long atomic64_##op##_return(long i, atomic64_t *v) \
{ \
register long x0 asm ("x0") = i; \
register atomic64_t *x1 asm ("x1") = v; \
\
asm volatile( \
__LL_SC_CALL64(op##_return) \
: "+r" (x0) \
: "r" (x1) \
: "x30", "memory"); \
\
return x0; \
}
#define ATOMIC64_OPS(op, asm_op) \
ATOMIC64_OP(op, asm_op) \
ATOMIC64_OP_RETURN(op, asm_op)
ATOMIC64_OPS(add, add)
ATOMIC64_OPS(sub, sub)
ATOMIC64_OP(and, and)
ATOMIC64_OP(andnot, bic)
ATOMIC64_OP(or, orr)
ATOMIC64_OP(xor, eor)
#undef ATOMIC64_OPS
#undef ATOMIC64_OP_RETURN
#undef ATOMIC64_OP
static inline long atomic64_cmpxchg(atomic64_t *ptr, long old, long new)
{
register unsigned long x0 asm ("x0") = (unsigned long)ptr;
register long x1 asm ("x1") = old;
register long x2 asm ("x2") = new;
asm volatile(
__LL_SC_CALL64(cmpxchg)
: "+r" (x0)
: "r" (x1), "r" (x2)
: "x30", "cc", "memory");
return x0;
}
static inline long atomic64_dec_if_positive(atomic64_t *v)
{
register unsigned long x0 asm ("x0") = (unsigned long)v;
asm volatile(
__LL_SC_CALL64(dec_if_positive)
: "+r" (x0)
:
: "x30", "cc", "memory");
return x0;
}
#endif /* __ASM_ATOMIC_LSE_H */

13
arch/arm64/lib/Makefile
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@ -3,3 +3,16 @@ lib-y := bitops.o clear_user.o delay.o copy_from_user.o \
clear_page.o memchr.o memcpy.o memmove.o memset.o \
memcmp.o strcmp.o strncmp.o strlen.o strnlen.o \
strchr.o strrchr.o
# Tell the compiler to treat all general purpose registers as
# callee-saved, which allows for efficient runtime patching of the bl
# instruction in the caller with an atomic instruction when supported by
# the CPU. Result and argument registers are handled correctly, based on
# the function prototype.
lib-$(CONFIG_ARM64_LSE_ATOMICS) += atomic_ll_sc.o
CFLAGS_atomic_ll_sc.o := -fcall-used-x0 -ffixed-x1 -ffixed-x2 \
-ffixed-x3 -ffixed-x4 -ffixed-x5 -ffixed-x6 \
-ffixed-x7 -fcall-saved-x8 -fcall-saved-x9 \
-fcall-saved-x10 -fcall-saved-x11 -fcall-saved-x12 \
-fcall-saved-x13 -fcall-saved-x14 -fcall-saved-x15 \
-fcall-saved-x16 -fcall-saved-x17 -fcall-saved-x18

3
arch/arm64/lib/atomic_ll_sc.c Normal file
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@ -0,0 +1,3 @@
#include <asm/atomic.h>
#define __ARM64_IN_ATOMIC_IMPL
#include <asm/atomic_ll_sc.h>