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

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

[Andre Przywara]

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(-)

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();
 
-- 
2.43.0

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

[Ben Horgan]

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@arm.com>

This looks good to me. Out of interest what led you to find this?

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

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();
>  

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@arm.com>
> 
> 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@arm.com>

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();
>>   
>