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

[Zeng Heng]

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