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

[Gavin Shan]

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@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.

Yeah, we can clean this up after that.

> Thanks,
>
> Ben

Thanks,
Gavin