Currently, cpus_set_cap() calls static_branch_enable_cpuslocked(), which
must take the jump_label mutex.
We call cpus_set_cap() in the secondary bringup path, from the idle
thread where interrupts are disabled. Taking a mutex in this path "is a
NONO" regardless of whether it's contended, and something we must avoid.
Additionally, the secondary CPU doesn't hold the percpu rwsem (as this
is held by the primary CPU), so this triggers a lockdep splat.
This patch fixes both issues by moving the static_key poking from
cpus_set_cap() into enable_cpu_capabilities(). To account for the static
keys being set later, cpus_have_const_cap() is updated to use another
static key to check whether the const cap keys have been initialised.
This means that users of cpus_have_const_cap() gain should only gain a
single additional NOP in the fast path once the const caps are
initialised, but should always see the current cap value.
This rework means that we can remove the *_cpuslocked() helpers added in
commit d54bb72551b999dd ("arm64/cpufeature: Use
static_branch_enable_cpuslocked()").
Fixes: efd9e03facd075f5 ("arm64: Use static keys for CPU features")
Signed-off-by: Mark Rutland <mark.rutl...@arm.com>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Marc Zyniger <marc.zyng...@arm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Sebastian Sewior <bige...@linutronix.de>
Cc: Suzuki Poulose <suzuki.poul...@arm.com>
Cc: Thomas Gleixner <t...@linutronix.de>
Cc: Will Deacon <will.dea...@arm.com>
---
arch/arm64/include/asm/cpufeature.h | 13 ++++++++++---
arch/arm64/kernel/cpu_errata.c | 9 +--------
arch/arm64/kernel/cpufeature.c | 25 ++++++++++++++++++++++---
3 files changed, 33 insertions(+), 14 deletions(-)
Catalin, Will, assuming you're happy with the patch, it will need to go via the
tip tree.
Since v1 [1]:
* Kill redundant update_cpu_errata_workarounds() prototype
* Introduce arm64_const_caps_ready
[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-May/505731.html
diff --git a/arch/arm64/include/asm/cpufeature.h
b/arch/arm64/include/asm/cpufeature.h
index 8a7ff73..428ee1f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -115,6 +115,7 @@ struct arm64_cpu_capabilities {
extern DECLARE_BITMAP(cpu_hwcaps, ARM64_NCAPS);
extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
+extern struct static_key_false arm64_const_caps_ready;
bool this_cpu_has_cap(unsigned int cap);
@@ -124,7 +125,7 @@ static inline bool cpu_have_feature(unsigned int num)
}
/* System capability check for constant caps */
-static inline bool cpus_have_const_cap(int num)
+static inline bool __cpus_have_const_cap(int num)
{
if (num >= ARM64_NCAPS)
return false;
@@ -138,6 +139,14 @@ static inline bool cpus_have_cap(unsigned int num)
return test_bit(num, cpu_hwcaps);
}
+static inline bool cpus_have_const_cap(int num)
+{
+ if (static_branch_likely(&arm64_const_caps_ready))
+ return __cpus_have_const_cap(num);
+ else
+ return cpus_have_cap(num);
+}
+
static inline void cpus_set_cap(unsigned int num)
{
if (num >= ARM64_NCAPS) {
@@ -145,7 +154,6 @@ static inline void cpus_set_cap(unsigned int num)
num, ARM64_NCAPS);
} else {
__set_bit(num, cpu_hwcaps);
- static_branch_enable_cpuslocked(&cpu_hwcap_keys[num]);
}
}
@@ -223,7 +231,6 @@ void update_cpu_capabilities(const struct
arm64_cpu_capabilities *caps,
void check_local_cpu_capabilities(void);
void update_cpu_errata_workarounds(void);
-void update_cpu_errata_workarounds_cpuslocked(void);
void __init enable_errata_workarounds(void);
void verify_local_cpu_errata_workarounds(void);
diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
index 57d60fa..2ed2a76 100644
--- a/arch/arm64/kernel/cpu_errata.c
+++ b/arch/arm64/kernel/cpu_errata.c
@@ -190,16 +190,9 @@ void verify_local_cpu_errata_workarounds(void)
}
}
-void update_cpu_errata_workarounds_cpuslocked(void)
-{
- update_cpu_capabilities(arm64_errata, "enabling workaround for");
-}
-
void update_cpu_errata_workarounds(void)
{
- get_online_cpus();
- update_cpu_errata_workarounds_cpuslocked();
- put_online_cpus();
+ update_cpu_capabilities(arm64_errata, "enabling workaround for");
}
void __init enable_errata_workarounds(void)
diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 803afae..4a89f59 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -986,8 +986,16 @@ void update_cpu_capabilities(const struct
arm64_cpu_capabilities *caps,
*/
void __init enable_cpu_capabilities(const struct arm64_cpu_capabilities *caps)
{
- for (; caps->matches; caps++)
- if (caps->enable && cpus_have_cap(caps->capability))
+ for (; caps->matches; caps++) {
+ unsigned int num = caps->capability;
+
+ if (!cpus_have_cap(num))
+ continue;
+
+ /* Ensure cpus_have_const_cap(num) works */
+ static_branch_enable(&cpu_hwcap_keys[num]);
+
+ if (caps->enable) {
/*
* Use stop_machine() as it schedules the work allowing
* us to modify PSTATE, instead of on_each_cpu() which
@@ -995,6 +1003,8 @@ void __init enable_cpu_capabilities(const struct
arm64_cpu_capabilities *caps)
* we return.
*/
stop_machine(caps->enable, NULL, cpu_online_mask);
+ }
+ }
}
/*
@@ -1086,7 +1096,7 @@ void check_local_cpu_capabilities(void)
* advertised capabilities.
*/
if (!sys_caps_initialised)
- update_cpu_errata_workarounds_cpuslocked();
+ update_cpu_errata_workarounds();
else
verify_local_cpu_capabilities();
}
@@ -1099,6 +1109,14 @@ static void __init setup_feature_capabilities(void)
enable_cpu_capabilities(arm64_features);
}
+DEFINE_STATIC_KEY_FALSE(arm64_const_caps_ready);
+EXPORT_SYMBOL(arm64_const_caps_ready);
+
+static void __init mark_const_caps_ready(void)
+{
+ static_branch_enable(&arm64_const_caps_ready);
+}
+
/*
* Check if the current CPU has a given feature capability.
* Should be called from non-preemptible context.
@@ -1134,6 +1152,7 @@ void __init setup_cpu_features(void)
/* Set the CPU feature capabilies */
setup_feature_capabilities();
enable_errata_workarounds();
+ mark_const_caps_ready();
setup_elf_hwcaps(arm64_elf_hwcaps);
if (system_supports_32bit_el0())
--
1.9.1
