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

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

On 2/17/26 15:59, Ben Horgan wrote:
> 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@huawei.com>
> 
> The change and justification looks good to me.
> 
> Acked-by: Ben Horgan <ben.horgan@arm.com>
> 

I'll add this on to the start of the current mpam resctrl series as even
though this is squashing an existing bug it can't be hit until mpam has
a user interface and so doesn't need to go as a fix.

Thanks,

Ben