lkml.org 
[lkml]   [2016]   [Aug]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 2/2] arm64: Use static keys for CPU features
Date
This patch adds static keys transparently for all the cpu_hwcaps
features by implementing an array of default-false static keys and
enabling them when detected. The cpus_have_cap() check uses the static
keys if the feature being checked is a constant, otherwise the compiler
generates the bitmap test.

Because of the early call to static_branch_enable() via
check_local_cpu_errata() -> update_cpu_capabilities(), the jump labels
are initialised in cpuinfo_store_boot_cpu().

Cc: Will Deacon <will.deacon@arm.com>
Cc: Suzuki K. Poulose <Suzuki.Poulose@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
arch/arm64/include/asm/cpufeature.h | 14 +++++++++++---
arch/arm64/kernel/cpufeature.c | 3 +++
arch/arm64/kernel/cpuinfo.c | 6 ++++++
3 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 7099f26e3702..c9dfb1e4c435 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -9,6 +9,8 @@
#ifndef __ASM_CPUFEATURE_H
#define __ASM_CPUFEATURE_H

+#include <linux/jump_label.h>
+
#include <asm/hwcap.h>
#include <asm/sysreg.h>

@@ -109,6 +111,7 @@ struct arm64_cpu_capabilities {
};

extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
+extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];

bool this_cpu_has_cap(unsigned int cap);

@@ -121,16 +124,21 @@ static inline bool cpus_have_cap(unsigned int num)
{
if (num >= ARM64_NCAPS)
return false;
- return test_bit(num, cpu_hwcaps);
+ if (__builtin_constant_p(num))
+ return static_branch_unlikely(&cpu_hwcap_keys[num]);
+ else
+ return test_bit(num, cpu_hwcaps);
}

static inline void cpus_set_cap(unsigned int num)
{
- if (num >= ARM64_NCAPS)
+ if (num >= ARM64_NCAPS) {
pr_warn("Attempt to set an illegal CPU capability (%d >= %d)\n",
num, ARM64_NCAPS);
- else
+ } else {
__set_bit(num, cpu_hwcaps);
+ static_branch_enable(&cpu_hwcap_keys[num]);
+ }
}

static inline int __attribute_const__
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 62272eac1352..919b2d0d68ae 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -46,6 +46,9 @@ unsigned int compat_elf_hwcap2 __read_mostly;

DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);

+DEFINE_STATIC_KEY_ARRAY_FALSE(cpu_hwcap_keys, ARM64_NCAPS);
+EXPORT_SYMBOL(cpu_hwcap_keys);
+
#define __ARM64_FTR_BITS(SIGNED, STRICT, TYPE, SHIFT, WIDTH, SAFE_VAL) \
{ \
.sign = SIGNED, \
diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c
index ed1b84fe6925..6a141e399daf 100644
--- a/arch/arm64/kernel/cpuinfo.c
+++ b/arch/arm64/kernel/cpuinfo.c
@@ -377,6 +377,12 @@ void cpuinfo_store_cpu(void)
void __init cpuinfo_store_boot_cpu(void)
{
struct cpuinfo_arm64 *info = &per_cpu(cpu_data, 0);
+
+ /*
+ * Initialise the static keys early as they may be enabled by
+ * check_local_cpu_errata() -> update_cpu_capabilities().
+ */
+ jump_label_init();
__cpuinfo_store_cpu(info);

boot_cpu_data = *info;
\
 
 \ /
  Last update: 2016-09-17 09:57    [W:0.048 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site