Re: [PATCH 21/33] arm_mpam: Extend reset logic to allow devices to be reset any time

[Ben Horgan <ben.horgan@arm.com>]

Hi James,

On 8/22/25 16:30, James Morse wrote:
> cpuhp callbacks aren't the only time the MSC configuration may need to
> be reset. Resctrl has an API call to reset a class.
> If an MPAM error interrupt arrives it indicates the driver has
> misprogrammed an MSC. The safest thing to do is reset all the MSCs
> and disable MPAM.
> 
> Add a helper to reset RIS via their class. Call this from mpam_disable(),
> which can be scheduled from the error interrupt handler.
> 
> Signed-off-by: James Morse <james.morse@arm.com>
> ---
>  drivers/resctrl/mpam_devices.c  | 62 +++++++++++++++++++++++++++++++--
>  drivers/resctrl/mpam_internal.h |  1 +
>  2 files changed, 61 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 759244966736..3516cbe8623e 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -915,8 +915,6 @@ static int mpam_reset_ris(void *arg)
>  	u16 partid, partid_max;
>  	struct mpam_msc_ris *ris = arg;
>  
> -	mpam_assert_srcu_read_lock_held();
> -
>  	if (ris->in_reset_state)
>  		return 0;
>  
> @@ -1569,6 +1567,66 @@ static void mpam_enable_once(void)
>  	       mpam_partid_max + 1, mpam_pmg_max + 1);
>  }
>  
> +static void mpam_reset_component_locked(struct mpam_component *comp)
> +{
> +	int idx;
> +	struct mpam_msc *msc;
> +	struct mpam_vmsc *vmsc;
> +	struct mpam_msc_ris *ris;
> +
> +	might_sleep();
> +	lockdep_assert_cpus_held();
> +
> +	idx = srcu_read_lock(&mpam_srcu);
> +	list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
> +		msc = vmsc->msc;
> +
> +		list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
> +			if (!ris->in_reset_state)
> +				mpam_touch_msc(msc, mpam_reset_ris, ris);
> +			ris->in_reset_state = true;
> +		}
> +	}
> +	srcu_read_unlock(&mpam_srcu, idx);
> +}
> +
> +static void mpam_reset_class_locked(struct mpam_class *class)
> +{
> +	int idx;
> +	struct mpam_component *comp;
> +
> +	lockdep_assert_cpus_held();
> +
> +	idx = srcu_read_lock(&mpam_srcu);
> +	list_for_each_entry_rcu(comp, &class->components, class_list)
> +		mpam_reset_component_locked(comp);
> +	srcu_read_unlock(&mpam_srcu, idx);
> +}
> +
> +static void mpam_reset_class(struct mpam_class *class)
> +{
> +	cpus_read_lock();
> +	mpam_reset_class_locked(class);
> +	cpus_read_unlock();
> +}
> +
> +/*
> + * Called in response to an error IRQ.
> + * All of MPAMs errors indicate a software bug, restore any modified
> + * controls to their reset values.
> + */
> +void mpam_disable(void)
> +{
> +	int idx;
> +	struct mpam_class *class;
> +
> +	idx = srcu_read_lock(&mpam_srcu);
> +	list_for_each_entry_srcu(class, &mpam_classes, classes_list,
> +				 srcu_read_lock_held(&mpam_srcu))

Why do you use list_for_each_entry_srcu() here when in other places you
use list_for_each_entry_rcu()?

> +		mpam_reset_class(class);
> +	srcu_read_unlock(&mpam_srcu, idx);
> +}
> +
>  /*
>   * Enable mpam once all devices have been probed.
>   * Scheduled by mpam_discovery_cpu_online() once all devices have been created.
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 466d670a01eb..b30fee2b7674 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -281,6 +281,7 @@ extern u8 mpam_pmg_max;
>  
>  /* Scheduled work callback to enable mpam once all MSC have been probed */
>  void mpam_enable(struct work_struct *work);
> +void mpam_disable(void);
>  
>  int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
>  				   cpumask_t *affinity);

Thanks,

Ben