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

[Andre Przywara]

Hi Ben,

thanks for having a look!

On 9/7/26 14:59, Ben Horgan wrote:
> Hi Andre,
>
> On 02/09/2026 15:37, 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>
>
> This looks good to me. Out of interest what led you to find this?

For Yin Li's RFC patch [06/15], I was looking around to find the proper 
type for cache-id, and stumbled upon this.

> Reviewed-by: Ben Horgan <ben.horgan@xxxxxxx>

Thanks!

Cheers,
Andre

> Thanks,
>
> Ben
>
> > ---
> >   drivers/resctrl/mpam_resctrl.c | 5 ++++-
> >   1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > 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();
> >