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

[Gavin Shan <gshan@redhat.com>]

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@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 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@vger.kernel.org
instead of linux-arm-kernel@lists.infradead.org. Since MPAM is a arm64 feature, it's
reasonable to post the patches to linux-arm-kernel@lists.infradead.org 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