Support static branches depending on the value of misaligned accesses.
This will be used by a later patch in the series. At any point in time,
this static branch will only be enabled if all online CPUs are
considered "fast".
Signed-off-by: Charlie Jenkins <charlie@xxxxxxxxxxxx>
Reviewed-by: Evan Green <evan@xxxxxxxxxxxx>
---
arch/riscv/include/asm/cpufeature.h | 2 +
arch/riscv/kernel/cpufeature.c | 90 +++++++++++++++++++++++++++++++++++--
2 files changed, 89 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index a418c3112cd6..7b129e5e2f07 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -133,4 +133,6 @@ static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsi
return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
}
+DECLARE_STATIC_KEY_FALSE(fast_misaligned_access_speed_key);
+
#endif
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index b3785ffc1570..b62baeb504d8 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -8,8 +8,10 @@
#include <linux/acpi.h>
#include <linux/bitmap.h>
+#include <linux/cpu.h>
#include <linux/cpuhotplug.h>
#include <linux/ctype.h>
+#include <linux/jump_label.h>
#include <linux/log2.h>
#include <linux/memory.h>
#include <linux/module.h>
@@ -44,6 +46,8 @@ struct riscv_isainfo hart_isa[NR_CPUS];
/* Performance information */
DEFINE_PER_CPU(long, misaligned_access_speed);
+static cpumask_t fast_misaligned_access;
+
/**
* riscv_isa_extension_base() - Get base extension word
*
@@ -643,6 +647,16 @@ static int check_unaligned_access(void *param)
(speed == RISCV_HWPROBE_MISALIGNED_FAST) ? "fast" : "slow");
per_cpu(misaligned_access_speed, cpu) = speed;
+
+ /*
+ * Set the value of fast_misaligned_access of a CPU. These operations
+ * are atomic to avoid race conditions.
+ */
+ if (speed == RISCV_HWPROBE_MISALIGNED_FAST)
+ cpumask_set_cpu(cpu, &fast_misaligned_access);
+ else
+ cpumask_clear_cpu(cpu, &fast_misaligned_access);
+
return 0;
}
@@ -655,13 +669,69 @@ static void check_unaligned_access_nonboot_cpu(void *param)
check_unaligned_access(pages[cpu]);
}
+DEFINE_STATIC_KEY_FALSE(fast_misaligned_access_speed_key);
+
+static void modify_unaligned_access_branches(cpumask_t *mask, int weight)
+{
+ if (cpumask_weight(mask) == weight)
+ static_branch_enable_cpuslocked(&fast_misaligned_access_speed_key);
+ else
+ static_branch_disable_cpuslocked(&fast_misaligned_access_speed_key);
+}
+
+static void set_unaligned_access_static_branches_except_cpu(int cpu)
+{
+ /*
+ * Same as set_unaligned_access_static_branches, except excludes the
+ * given CPU from the result. When a CPU is hotplugged into an offline
+ * state, this function is called before the CPU is set to offline in
+ * the cpumask, and thus the CPU needs to be explicitly excluded.
+ */
+
+ cpumask_t fast_except_me;
+
+ cpumask_and(&fast_except_me, &fast_misaligned_access, cpu_online_mask);
+ cpumask_clear_cpu(cpu, &fast_except_me);
+
+ modify_unaligned_access_branches(&fast_except_me, num_online_cpus() - 1);
+}
+
+static void set_unaligned_access_static_branches(void)
+{
+ /*
+ * This will be called after check_unaligned_access_all_cpus so the
+ * result of unaligned access speed for all CPUs will be available.
+ *
+ * To avoid the number of online cpus changing between reading
+ * cpu_online_mask and calling num_online_cpus, cpus_read_lock must be
+ * held before calling this function.
+ */
+
+ cpumask_t fast_and_online;
+
+ cpumask_and(&fast_and_online, &fast_misaligned_access, cpu_online_mask);
+
+ modify_unaligned_access_branches(&fast_and_online, num_online_cpus());
+}
+
+static int lock_and_set_unaligned_access_static_branch(void)
+{
+ cpus_read_lock();
+ set_unaligned_access_static_branches();
+ cpus_read_unlock();
+
+ return 0;
+}
+
+arch_initcall_sync(lock_and_set_unaligned_access_static_branch);
+
static int riscv_online_cpu(unsigned int cpu)
{
static struct page *buf;
/* We are already set since the last check */
if (per_cpu(misaligned_access_speed, cpu) != RISCV_HWPROBE_MISALIGNED_UNKNOWN)
- return 0;
+ goto exit;
buf = alloc_pages(GFP_KERNEL, MISALIGNED_BUFFER_ORDER);
if (!buf) {
@@ -671,6 +741,17 @@ static int riscv_online_cpu(unsigned int cpu)
check_unaligned_access(buf);
__free_pages(buf, MISALIGNED_BUFFER_ORDER);
+
+exit:
+ set_unaligned_access_static_branches();
+
+ return 0;
+}
+
+static int riscv_offline_cpu(unsigned int cpu)
+{
+ set_unaligned_access_static_branches_except_cpu(cpu);
+
return 0;
}
@@ -705,9 +786,12 @@ static int check_unaligned_access_all_cpus(void)
/* Check core 0. */
smp_call_on_cpu(0, check_unaligned_access, bufs[0], true);
- /* Setup hotplug callback for any new CPUs that come online. */
+ /*
+ * Setup hotplug callbacks for any new CPUs that come online or go
+ * offline.
+ */
cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "riscv:online",
- riscv_online_cpu, NULL);
+ riscv_online_cpu, riscv_offline_cpu);
out:
unaligned_emulation_finish();
--
2.43.0
