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@xxxxxxx>

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

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

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();
>