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

[Yin Li <yin.li@oss.qualcomm.com>]

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@arm.com>
>> ---
>>   drivers/resctrl/mpam_resctrl.c | 5 ++++-
>>   1 file changed, 4 insertions(+), 1 deletion(-)
>>
> 
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> 
>> 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@oss.qualcomm.com/

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,
Yin



> Thanks,
> Gavin
> 

-- 
Thx and BRs,
Yin