Re: [PATCH v1 04/11] arm_mpam: Add missing mon_sel locking in MBWU restore

[Ben Horgan]

Hi Gavin,

On 7/16/26 05:29, Gavin Shan wrote:
> On 7/10/26 9:55 PM, Ben Horgan wrote:
>> The mon_sel_lock is used to protect the mbwu_state, as well as h/w accesses
>> that use MPAMCFG_MON_SEL. However, in mpam_restore_mbwu_state() mbwu_state
>> is accessed without holding the mon_sel_lock.
>>
>> Add the missing locking.
>>
>> Fixes: 41e8a14950e1 ("arm_mpam: Track bandwidth counter state for power management")
>> Signed-off-by: Ben Horgan <ben.horgan@xxxxxxx>
>> ---
>>   drivers/resctrl/mpam_devices.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
>> index 11b10c3bc334..b34e2a368516 100644
>> --- a/drivers/resctrl/mpam_devices.c
>> +++ b/drivers/resctrl/mpam_devices.c
>> @@ -1648,16 +1648,24 @@ static int mpam_restore_mbwu_state(void *_ris)
>>       u64 val;
>>       struct mon_read mwbu_arg;
>>       struct mpam_msc_ris *ris = _ris;
>> +    struct mpam_msc *msc = ris->vmsc->msc;
>>       struct mpam_class *class = ris->vmsc->comp->class;
>>         for (i = 0; i < ris->props.num_mbwu_mon; i++) {
>> +        if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
>> +            return -EIO;
>> +
> 
> The code can be simplified by avoiding the unnecessary nested conditional statement,
> something like below:
> 
>         if (!ris->mbwu_state[i].enabled) {
>             mpam_mon_sel_unlock(msc);
>             continue;
>         }
> 
>         mwbu_arg.ris = ris;
>                 mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
>         mwbu_arg.type = mpam_msmon_choose_counter(class);
>         mwbu_arg.val = &val;
> 
>                 mpam_mon_sel_unlock(msc);
> 
>                 __ris_msmon_read(&mwbu_arg);
> 
>>           if (ris->mbwu_state[i].enabled) {
>>               mwbu_arg.ris = ris;
>>               mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
>>               mwbu_arg.type = mpam_msmon_choose_counter(class);
>>               mwbu_arg.val = &val;
>>   +            mpam_mon_sel_unlock(msc);
>> +
>>               __ris_msmon_read(&mwbu_arg);
>> +        } else {
>> +            mpam_mon_sel_unlock(msc);
>>           }
>>       }
>>   

Ok. I think it will be clearer what's best here once Andre's error propagation in his MPAM-Fb series
has crystalized.

Thanks,

Ben

> 
> Thanks,
> Gavin
>