[PATCH v2] arm64: topology: add source check in arch_cpu_idle_enter()

[PATCH v2] arm64: topology: add source check in arch_cpu_idle_enter()

[seanwang1]

arch_cpu_idle_enter() directly calls amu_scale_freq_tick() to update
arch_freq_scale when a CPU enters idle. This bypasses the sft_data
pointer check that topology_clear_scale_freq_source() relies on.

As a result, even after calling topology_clear_scale_freq_source()
with SCALE_FREQ_SOURCE_ARCH to disable AMU-based frequency scaling,
the arch_freq_scale value can still be modified by AMU counters when
the CPU goes idle through the arch_cpu_idle_enter() path.

Add topology_scale_freq_source() helper to check whether a specific
frequency scaling source is currently registered for a CPU. Use it
in arch_cpu_idle_enter() to verify that AMU is the active source
before calling amu_scale_freq_tick().

This ensures that topology_clear_scale_freq_source() properly
disables AMU updates in both the tick path (already handled by
topology_scale_freq_tick()) and the idle path.

Co-developed-by: Xuewen Yan <xuewen.yan@unisoc.com>
Signed-off-by: Sean Wang <seanwang1@lenovo.com>
Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
---
 arch/arm64/kernel/topology.c  |  3 +++
 drivers/base/arch_topology.c  | 14 ++++++++++++++
 include/linux/arch_topology.h |  1 +
 3 files changed, 18 insertions(+)

diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
index b32f13358fbb..cae5da68d5ec 100644
--- a/arch/arm64/kernel/topology.c
+++ b/arch/arm64/kernel/topology.c
@@ -173,6 +173,9 @@ void arch_cpu_idle_enter(void)
 	if (!amu_fie_cpu_supported(cpu))
 		return;
 
+	if (!topology_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpu))
+		return;
+
 	/* Kick in AMU update but only if one has not happened already */
 	if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
 	    time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)))
diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
index 8c5e47c28d9a..dfc2574a5588 100644
--- a/drivers/base/arch_topology.c
+++ b/drivers/base/arch_topology.c
@@ -127,6 +127,20 @@ void topology_clear_scale_freq_source(enum scale_freq_source source,
 }
 EXPORT_SYMBOL_GPL(topology_clear_scale_freq_source);
 
+bool topology_scale_freq_source(enum scale_freq_source source, unsigned int cpu)
+{
+	struct scale_freq_data *sfd;
+	bool ret;
+
+	rcu_read_lock_sched();
+	sfd = rcu_dereference_sched(*per_cpu_ptr(&sft_data, cpu));
+	ret = (sfd && sfd->source == source);
+	rcu_read_unlock_sched();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(topology_scale_freq_source);
+
 void topology_scale_freq_tick(void)
 {
 	struct scale_freq_data *sfd = rcu_dereference_sched(*this_cpu_ptr(&sft_data));
diff --git a/include/linux/arch_topology.h b/include/linux/arch_topology.h
index ebd7f8935f96..803382f599a2 100644
--- a/include/linux/arch_topology.h
+++ b/include/linux/arch_topology.h
@@ -48,6 +48,7 @@ struct scale_freq_data {
 void topology_scale_freq_tick(void);
 void topology_set_scale_freq_source(struct scale_freq_data *data, const struct cpumask *cpus);
 void topology_clear_scale_freq_source(enum scale_freq_source source, const struct cpumask *cpus);
+bool topology_scale_freq_source(enum scale_freq_source source, unsigned int cpu);
 
 DECLARE_PER_CPU(unsigned long, hw_pressure);
 
-- 
2.25.1

Re: [PATCH v2] arm64: topology: add source check in arch_cpu_idle_enter()

[Greg Kroah-Hartman]

On Mon, Aug 10, 2026 at 06:20:06PM +0800, seanwang1 wrote:
> arch_cpu_idle_enter() directly calls amu_scale_freq_tick() to update
> arch_freq_scale when a CPU enters idle. This bypasses the sft_data
> pointer check that topology_clear_scale_freq_source() relies on.
> 
> As a result, even after calling topology_clear_scale_freq_source()
> with SCALE_FREQ_SOURCE_ARCH to disable AMU-based frequency scaling,
> the arch_freq_scale value can still be modified by AMU counters when
> the CPU goes idle through the arch_cpu_idle_enter() path.
> 
> Add topology_scale_freq_source() helper to check whether a specific
> frequency scaling source is currently registered for a CPU. Use it
> in arch_cpu_idle_enter() to verify that AMU is the active source
> before calling amu_scale_freq_tick().
> 
> This ensures that topology_clear_scale_freq_source() properly
> disables AMU updates in both the tick path (already handled by
> topology_scale_freq_tick()) and the idle path.
> 
> Co-developed-by: Xuewen Yan <xuewen.yan@unisoc.com>
> Signed-off-by: Sean Wang <seanwang1@lenovo.com>
> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> ---

The From: line does not match your signed-off-by name :(

Re: [PATCH v2] arm64: topology: add source check in arch_cpu_idle_enter()

[Sumit Gupta]

On 10/08/26 15:50, seanwang1 wrote:
> External email: Use caution opening links or attachments
>
>
> arch_cpu_idle_enter() directly calls amu_scale_freq_tick() to update
> arch_freq_scale when a CPU enters idle. This bypasses the sft_data
> pointer check that topology_clear_scale_freq_source() relies on.
>
> As a result, even after calling topology_clear_scale_freq_source()
> with SCALE_FREQ_SOURCE_ARCH to disable AMU-based frequency scaling,
> the arch_freq_scale value can still be modified by AMU counters when
> the CPU goes idle through the arch_cpu_idle_enter() path.
>
> Add topology_scale_freq_source() helper to check whether a specific
> frequency scaling source is currently registered for a CPU. Use it
> in arch_cpu_idle_enter() to verify that AMU is the active source
> before calling amu_scale_freq_tick().
>
> This ensures that topology_clear_scale_freq_source() properly
> disables AMU updates in both the tick path (already handled by
> topology_scale_freq_tick()) and the idle path.
>
> Co-developed-by: Xuewen Yan <xuewen.yan@unisoc.com>
> Signed-off-by: Sean Wang <seanwang1@lenovo.com>
> Signed-off-by: Xuewen Yan <xuewen.yan@unisoc.com>
> ---
>   arch/arm64/kernel/topology.c  |  3 +++
>   drivers/base/arch_topology.c  | 14 ++++++++++++++
>   include/linux/arch_topology.h |  1 +
>   3 files changed, 18 insertions(+)
>
> diff --git a/arch/arm64/kernel/topology.c b/arch/arm64/kernel/topology.c
> index b32f13358fbb..cae5da68d5ec 100644
> --- a/arch/arm64/kernel/topology.c
> +++ b/arch/arm64/kernel/topology.c
> @@ -173,6 +173,9 @@ void arch_cpu_idle_enter(void)
>          if (!amu_fie_cpu_supported(cpu))
>                  return;
>
> +       if (!topology_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpu))
> +               return;
> +
>          /* Kick in AMU update but only if one has not happened already */
>          if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
>              time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)))

How about moving it into the condition below, so we only take the RCU
read side when an update is due rather than on every idle entry?

     if (housekeeping_cpu(cpu, HK_TYPE_TICK) &&
time_is_before_jiffies(per_cpu(cpu_amu_samples.last_scale_update, cpu)) &&
         topology_scale_freq_source(SCALE_FREQ_SOURCE_ARCH, cpu))
         amu_scale_freq_tick();

> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 8c5e47c28d9a..dfc2574a5588 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -127,6 +127,20 @@ void topology_clear_scale_freq_source(enum scale_freq_source source,
>   }
>   EXPORT_SYMBOL_GPL(topology_clear_scale_freq_source);
>
> +bool topology_scale_freq_source(enum scale_freq_source source, unsigned int cpu)

%s/topology_scale_freq_source/topology_is_scale_freq_source/ ?


> +{
> +       struct scale_freq_data *sfd;
> +       bool ret;
> +
> +       rcu_read_lock_sched();
> +       sfd = rcu_dereference_sched(*per_cpu_ptr(&sft_data, cpu));
> +       ret = (sfd && sfd->source == source);
> +       rcu_read_unlock_sched();
> +
> +       return ret;
> +}
> +EXPORT_SYMBOL_GPL(topology_scale_freq_source);
> +

Do we need to export it?

Thanks,
Sumit
....