Re: [RFC PATCH v2 08/10] arm_mpam: resctrl: Require a component for each monitoring event

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

Hi Reinette,

Seems good to me.

Reviewed-by: Ben Horgan <ben.horgan@arm.com>

On 19/10/2026 23:07, Reinette Chatre wrote:
> Setting up a monitoring domain looks up, for each monitoring event, the
> component of the event's class that contains the CPU and records it in
> the domain. Reading and resetting the event's counters in the domain
> then use the recorded component.
> 
> If an event's class has no component for the CPU, the domain is still
> set up as long as another event's class has one, and the event is left
> without a component. Reading or resetting the event's counters in that
> domain then dereferences a NULL component. This is not expected to
> happen since only classes that cover all possible CPUs are picked for
> monitoring.
> 
> Fail setting up the monitoring domain, with a warning, if an event's
> class has no component for the CPU, so that every event of a monitoring
> domain has a component.
> 
> Keep the check that at least one component was found. It now only fails
> if no event has a class, and so captures that a resource that supports
> monitoring has at least one monitoring event with a class.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
> ---
>  drivers/resctrl/mpam_resctrl.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/mpam_resctrl.c
> index 63c5bf45856d..36a924734484 100644
> --- a/drivers/resctrl/mpam_resctrl.c
> +++ b/drivers/resctrl/mpam_resctrl.c
> @@ -1661,9 +1661,11 @@ static int mpam_resctrl_setup_mon_domain(unsigned int cpu,
>  			continue;       // dummy resource
>  
>  		mon_comp = find_component(mon->class, cpu);
> +		if (WARN_ON_ONCE(!mon_comp))
> +			return -EFAULT;
> +
>  		dom->mon_comp[eventid] = mon_comp;
> -		if (mon_comp)
> -			any_mon_comp = mon_comp;
> +		any_mon_comp = mon_comp;
>  	}
>  	if (WARN_ON_ONCE(!any_mon_comp))
>  		return -EFAULT;