Re: [PATCH] arm_mpam: Fix MPAM reset on resctrl unmount by clearing in_reset_state

[Ben Horgan]

Hi Zeng,

On 2/13/26 07:50, Zeng Heng wrote:
> When resctrl is unmounted, MPAM components should be reset to default
> configurations to avoid impacting system performance. However, after
> a user updates MPAM configuration via mpam_apply_config(), the
> in_reset_state flag remains true, causing mpam_reset_ris() to skip
> the actual register restoration on subsequent resets.
> 
> For example, after mounting resctrl and modifying the root group's
> schemata (e.g., changing MBMAX/MBMIN values), unmounting resctrl

nit: MBMIN isn't currently supported in resctrl. I'd just drop the
part in brackets.

> would leave the modified MPAM settings in hardware registers since
> mpam_reset_ris() returns early due to in_reset_state still being true.
> This results in persistent performance restrictions even after resctrl
> is umounted.
> 
> Fix by clearing in_reset_state to false immediately after successful
> configuration application, ensuring that the next reset operation
> properly restores MPAM register defaults.
> 
> Fixes: f188a36ca241 ("arm_mpam: Reset MSC controls from cpuhp callbacks")

mpam_apply_config() doesn't exist in this commit. I would have expected:
Fixes: 09b89d2a72f3 ("arm_mpam: Allow configuration to be applied and restored during cpu online")

> Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>

The change and justification looks good to me.

Acked-by: Ben Horgan <ben.horgan@xxxxxxx>

Thanks,

Ben

> ---
> The in_reset_state state machine has been carefully reviewed, particularly
> the handling in mpam_cpu_online() where the flag is checked before
> applying configurations. in_reset_state indicates whether the RIS is
> currently using default configurations. This change aligns with the
> original design intent and does not introduce semantic breakage to
> existing state transitions.
> ---
>  drivers/resctrl/mpam_devices.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 460ea98a1c92..044227ee033f 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -2932,6 +2932,7 @@ int mpam_apply_config(struct mpam_component *comp, u16 partid,
>  					 srcu_read_lock_held(&mpam_srcu)) {
>  			arg.ris = ris;
>  			mpam_touch_msc(msc, __write_config, &arg);
> +			ris->in_reset_state = false;
>  		}
>  		mutex_unlock(&msc->cfg_lock);
>  	}
> --
> 2.25.1
>