Re: [PATCH v2 18/29] arm_mpam: Register and enable IRQs

James Morse
2025-10-03T18:03:19Z

Hi Fenghua,

On 25/09/2025 07:33, Fenghua Yu wrote:
> On 9/10/25 13:42, James Morse wrote:
>> Register and enable error IRQs. All the MPAM error interrupts indicate a
>> software bug, e.g. out of range partid. If the error interrupt is ever
>> signalled, attempt to disable MPAM.
>>
>> Only the irq handler accesses the ESR register, so no locking is needed.
>> The work to disable MPAM after an error needs to happen at process
>> context as it takes mutex. It also unregisters the interrupts, meaning
>> it can't be done from the threaded part of a threaded interrupt.
>> Instead, mpam_disable() gets scheduled.
>>
>> Enabling the IRQs in the MSC may involve cross calling to a CPU that
>> can access the MSC.
>>
>> Once the IRQ is requested, the mpam_disable() path can be called
>> asynchronously, which will walk structures sized by max_partid. Ensure
>> this size is fixed before the interrupt is requested.

>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index a9d3c4b09976..e7e4afc1ea95 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -1318,11 +1405,172 @@ static void mpam_enable_merge_features(struct list_head

>> +static void mpam_unregister_irqs(void)
>> +{
>> +    int irq, idx;
>> +    struct mpam_msc *msc;
>> +
>> +    cpus_read_lock();
>> +    /* take the lock as free_irq() can sleep */
>> +    idx = srcu_read_lock(&mpam_srcu);

> guard(srcu)(&mpam_srcu);

Yes - Jonathan already suggested this.

>> +    list_for_each_entry_srcu(msc, &mpam_all_msc, all_msc_list,
>> +                 srcu_read_lock_held(&mpam_srcu)) {
>> +        irq = platform_get_irq_byname_optional(msc->pdev, "error");
>> +        if (irq <= 0)
>> +            continue;
>> +
>> +        if (test_and_clear_bit(MPAM_ERROR_IRQ_HW_ENABLED, &msc->error_irq_flags))
>> +            mpam_touch_msc(msc, mpam_disable_msc_ecr, msc);
>> +
>> +        if (test_and_clear_bit(MPAM_ERROR_IRQ_REQUESTED, &msc->error_irq_flags)) {
>> +            if (irq_is_percpu(irq)) {
>> +                msc->reenable_error_ppi = 0;
>> +                free_percpu_irq(irq, msc->error_dev_id);
>> +            } else {
>> +                devm_free_irq(&msc->pdev->dev, irq, msc);
>> +            }
>> +        }
>> +    }
>> +    srcu_read_unlock(&mpam_srcu, idx);
>> +    cpus_read_unlock();
>> +}

James