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

Jonathan Cameron
2025-09-12T12:12:24Z

On Wed, 10 Sep 2025 20:42:58 +0000
James Morse <james.morse@arm.com> 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.
>
> CC: Rohit Mathew <rohit.mathew@arm.com>
> Tested-by: Rohit Mathew <rohit.mathew@arm.com>
> Signed-off-by: James Morse <james.morse@arm.com>
A few comments inline.

> @@ -1318,11 +1405,172 @@ static void mpam_enable_merge_features(struct list_head *all_classes_list)
> }
> }
>
> +static char *mpam_errcode_names[16] = {
> + [0] = "No error",

I think you had a bunch of defines for these in an earlier patch. Can we use
that to index here instead of [0] etc.

> + [1] = "PARTID_SEL_Range",
> + [2] = "Req_PARTID_Range",
> + [3] = "MSMONCFG_ID_RANGE",
> + [4] = "Req_PMG_Range",
> + [5] = "Monitor_Range",
> + [6] = "intPARTID_Range",
> + [7] = "Unexpected_INTERNAL",
> + [8] = "Undefined_RIS_PART_SEL",
> + [9] = "RIS_No_Control",
> + [10] = "Undefined_RIS_MON_SEL",
> + [11] = "RIS_No_Monitor",
> + [12 ... 15] = "Reserved"
> +};

> +static void mpam_unregister_irqs(void)
> +{
> + int irq, idx;
> + struct mpam_msc *msc;
> +
> + cpus_read_lock();

guard(cpus_read_lock)();
guard(srcu)(&mpam_srcu);

> + /* take the lock as free_irq() can sleep */
> + idx = srcu_read_lock(&mpam_srcu);
> + 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();
> +}
> +
> static void mpam_enable_once(void)
> {
> - mutex_lock(&mpam_list_lock);
> - mpam_enable_merge_features(&mpam_classes);
> - mutex_unlock(&mpam_list_lock);
> + int err;
>
> /*
> * Once the cpuhp callbacks have been changed, mpam_partid_max can no
> @@ -1332,6 +1580,27 @@ static void mpam_enable_once(void)
> partid_max_published = true;
> spin_unlock(&partid_max_lock);
>
> + /*
> + * If all the MSC have been probed, enabling the IRQs happens next.
> + * That involves cross-calling to a CPU that can reach the MSC, and
> + * the locks must be taken in this order:
> + */
> + cpus_read_lock();
> + mutex_lock(&mpam_list_lock);
> + mpam_enable_merge_features(&mpam_classes);
> +
> + err = mpam_register_irqs();
> + if (err)
> + pr_warn("Failed to register irqs: %d\n", err);

Perhaps move the print into the if (err) below?

> +
> + mutex_unlock(&mpam_list_lock);
> + cpus_read_unlock();
> +
> + if (err) {
> + schedule_work(&mpam_broken_work);
> + return;
> + }

> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 6e047fbd3512..f04a9ef189cf 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -32,6 +32,10 @@ struct mpam_garbage {
> struct platform_device *pdev;
> };
>
> +/* Bit positions for error_irq_flags */
> +#define MPAM_ERROR_IRQ_REQUESTED 0
> +#define MPAM_ERROR_IRQ_HW_ENABLED 1

If there aren't going to be load more of these (I've not really thought
about whether there might) then using a bitmap for these seems to add complexity
that we wouldn't see with
bool error_irq_req;
bool error_irq_hw_enabled;

> +
> struct mpam_msc {
> /* member of mpam_all_msc */
> struct list_head all_msc_list;
> @@ -46,6 +50,11 @@ struct mpam_msc {
> struct pcc_mbox_chan *pcc_chan;
> u32 nrdy_usec;
> cpumask_t accessibility;
> + bool has_extd_esr;
> +
> + int reenable_error_ppi;
> + struct mpam_msc * __percpu *error_dev_id;
> +
> atomic_t online_refs;
>
> /*
> @@ -54,6 +63,7 @@ struct mpam_msc {
> */
> struct mutex probe_lock;
> bool probed;
> + unsigned long error_irq_flags;
> u16 partid_max;
> u8 pmg_max;
> unsigned long ris_idxs;