Re: [PATCH v3 06/16] arm_mpam: propagate MSC read errors for __ris_msmon_read()

[Lee Trager <lee@trager.us>]

On 7/10/26 7:45 AM, Andre Przywara wrote:

> @@ -1748,6 +1758,7 @@ static int mpam_restore_mbwu_state(void *_ris)
>   {
>   	int i;
>   	u64 val;
> +	int ret = 0;
>   	struct mon_read mwbu_arg;
>   	struct mpam_msc_ris *ris = _ris;
>   	struct mpam_class *class = ris->vmsc->comp->class;
> @@ -1760,10 +1771,14 @@ static int mpam_restore_mbwu_state(void *_ris)
>   			mwbu_arg.val = &val;
>   
>   			__ris_msmon_read(&mwbu_arg);
> +			if (mwbu_arg.err) {
> +				ret = mwbu_arg.err;
> +				break;
> +			}
>   		}
>   	}
>   
> -	return 0;
> +	return ret;
>   }
>   
>   /* Call with MSC cfg_lock held */


mwbu_arg is never initialized and __ris_msmon_read() only writes ->err 
on failure. If on a successful read mwb_arg.err tests stack garbage it 
can spuriously break ot of the loop, leaving the remaining monitors 
unrestored, and return a junk error code.

Setting `struct mon_read mwbu_arg = {};` matches what mpam_msmon_read() 
already does. Additionally val should be initialized to 0 too. 
__ris_msmon_reaD() does *m->val += now, and although the result is 
discarded here, KMSAN would flag the uninitialized read.