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

[Gavin Shan <gshan@redhat.com>]

Hi Ben,

On 7/16/26 7:31 PM, Ben Horgan wrote:
> 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@arm.com>
>>> ---
>>>    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.
> 

Yeah, we can clean this up after that.

> Thanks,
> 
> Ben
> 

Thanks,
Gavin