Re: [PATCH] arm_mpam: resctrl: Catch and propagate error from get_cpu_cacheinfo_id()

[Gavin Shan]

Hi Yin,

On 9/14/26 4:25 PM, Yin Li wrote:
> On 9/14/2026 2:14 PM, Gavin Shan wrote:
> > On 9/3/26 12:37 AM, Andre Przywara wrote:
> > > get_cpu_cacheinfo_id() can fail, in which case it returns a negative
> > > error value.
> > >
> > > Check the returned value for this error condition, before passing the
> > > value on to other code, which would hide the negative number in some high
> > > value in the unsigned type.
> > >
> > > Fixes: 36528c7681b8 ("arm_mpam: resctrl: Add support for 'MB' resource")
> > > Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> > > ---
> > >   drivers/resctrl/mpam_resctrl.c | 5 ++++-
> > >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > Reviewed-by: Gavin Shan <gshan@xxxxxxxxxx>
> >
> > > diff --git a/drivers/resctrl/mpam_resctrl.c b/drivers/resctrl/ mpam_resctrl.c
> > > index 9d223057953ab..a5e661eff86d7 100644
> > > --- a/drivers/resctrl/mpam_resctrl.c
> > > +++ b/drivers/resctrl/mpam_resctrl.c
> > > @@ -786,7 +786,10 @@ static u32 get_mba_min(struct mpam_props *cprops)
> > >   /* Find the L3 cache that has affinity with this CPU */
> > >   static int find_l3_equivalent_bitmask(int cpu, cpumask_var_t tmp_cpumask)
> > >   {
> > > -    u32 cache_id = get_cpu_cacheinfo_id(cpu, 3);
> > > +    int cache_id = get_cpu_cacheinfo_id(cpu, 3);
> > > +
> > > +    if (cache_id < 0)
> > > +        return -ENOENT;
> > >       lockdep_assert_cpus_held();
> >
> > find_l3_equivalent_bitmask() passes @cache_id to find_l3_equivalent_bitmask() as
> > a 'unsigned long' argument. Actually, it can be 'u32'. It's not directly related
> > to this patch though.
> >
> > int mpam_get_cpumask_from_cache_id(unsigned long cache_id, ...);
> >
> > can be:
> >
> > int mpam_get_cpumask_from_cache_id(u32 cache_id, ...);
>
> Hi Gavin,
>
> Thanks for pointing this out. I've made exactly this change in my MPAM
> DT series (v2, in preparation) — mpam_get_cpumask_from_cache_id() is
> changed from unsigned long to u32 there, along with the related cache-id
> variables.
> https://lore.kernel.org/all/20260811-mpam-resctrl-dt-knp-support-v1-6-ea6397bead59@xxxxxxxxxxxxxxxx/
>
> I'm about to post v2 of that series and will make sure you're on Cc, in
> case you'd like to take a look.

Thanks for head-up, please keep me on the cc list. I would like to review
if I get bandwidth, but no promise :)

I noticed RFCv1 series of DT support for MPAM was posted to linux-kernel@xxxxxxxxxxxxxxx
instead of linux-arm-kernel@xxxxxxxxxxxxxxxxxxx. Since MPAM is a arm64 feature, it's
reasonable to post the patches to linux-arm-kernel@xxxxxxxxxxxxxxxxxxx at the same time.

MAINTAINERS doesn't indicates a maillist for MPAM patches in section "MPAM DRIVER". I guess it
would be something worthy to be added.

Thanks,
Gavin