Re: [PATCH v5 03/10] arm_mpam: propagate MSC access errors for MBWU counters

[Lee Trager <lee@trager.us>]

On 7/29/26 6:41 AM, Andre Przywara wrote:

> @@ -1767,6 +1781,7 @@ static int mpam_save_mbwu_state(void *arg)
>   {
>   	int i;
>   	u64 val;
> +	int ret;
>   	struct mon_cfg *cfg;
>   	u32 cur_flt, cur_ctl, mon_sel;
>   	struct mpam_msc_ris *ris = arg;
> @@ -1777,7 +1792,8 @@ static int mpam_save_mbwu_state(void *arg)
>   		mbwu_state = &ris->mbwu_state[i];
>   		cfg = &mbwu_state->cfg;
>   
> -		if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
> +		ACQUIRE(mon_sel_lock, guard)(msc);
> +		if (ACQUIRE_ERR(mon_sel_lock, &guard))
>   			return -EIO;
>   
>   		mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, i) |
> @@ -1788,7 +1804,9 @@ static int mpam_save_mbwu_state(void *arg)
>   		mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
>   
>   		if (mpam_ris_has_mbwu_long_counter(ris)) {
> -			val = mpam_msc_read_mbwu_l(msc);
> +			ret = mpam_msc_read_mbwu_l(msc, &val);
> +			if (ret)
> +				return ret;
>   			mpam_msc_zero_mbwu_l(msc);
>   		} else {
>   			u32 val32;
I think checking for (val & MSMON____L_NRDRY) is still required before 
updating the saved state. mpam_msc_read_mbw_l() can return 0 while 
setting val to MSMON___L_NRDY when it cannot obtain a stable value. The 
state saving path later adds val to mbwu_state->correction, so the 
sentinel would corrupt the saved correction. Additionally, as Ben noted 
during the v3 review, hardware may also set the NRDY bit.
> @@ -1804,7 +1822,6 @@ static int mpam_save_mbwu_state(void *arg)
>   		cfg->partid = FIELD_GET(MSMON_CFG_x_FLT_PARTID, cur_flt);
>   		mbwu_state->correction += val;
>   		mbwu_state->enabled = FIELD_GET(MSMON_CFG_x_CTL_EN, cur_ctl);
> -		mpam_mon_sel_unlock(msc);
>   	}
>   
>   	return 0;