Re: [PATCH v5 05/10] arm_mpam: propagate MSC access errors for __ris_msmon_read()

[Ben Horgan]

Hi Andre,

On 7/29/26 14:41, Andre Przywara wrote:
> Allow the function for RIS accesses to return an error, and propagate
> read and write errors from the lower level up.
> This function is a bit special, since it can be called via an SMP
> helper, so the prototype must stay as void. So propagate any errors
> using the "err" field in the struct passed in as the sole argument to
> that function.
> 
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> Reviewed-by: Jonathan Cameron <jonathan.cameron@xxxxxxxxxxxxxxxx>
> ---
>  drivers/resctrl/mpam_devices.c | 36 +++++++++++++++++++++++++---------
>  1 file changed, 27 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index 9d9f0c635527..44eafef1e7ab 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1333,6 +1333,10 @@ static u64 mpam_msmon_overflow_val(enum mpam_device_features type,
>  	return overflow_val;
>  }
>  
> +/*
> + * This function might be called via smp_call_function_any(), so propagate
> + * errors inside the arg struct.
> + */
>  static void __ris_msmon_read(void *arg)
>  {
>  	u64 now;
> @@ -1356,7 +1360,9 @@ static void __ris_msmon_read(void *arg)
>  
>  	mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
>  		  FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
> -	mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
> +	m->err = mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
> +	if (m->err)
> +		return;
>  
>  	switch (m->type) {
>  	case mpam_feat_msmon_mbwu_31counter:
> @@ -1376,7 +1382,9 @@ static void __ris_msmon_read(void *arg)
>  	 * Read the existing configuration to avoid re-writing the same values.
>  	 * This saves waiting for 'nrdy' on subsequent reads.
>  	 */
> -	read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> +	m->err = read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
> +	if (m->err)
> +		return;
>  
>  	if (mpam_feat_msmon_mbwu_31counter == m->type)
>  		overflow = cur_ctl & MSMON_CFG_x_CTL_OFLOW_STATUS;
> @@ -1390,18 +1398,24 @@ static void __ris_msmon_read(void *arg)
>  			  cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);
>  
>  	if (config_mismatch || reset_on_next_read) {
> -		write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> +		m->err = write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
> +		if (m->err)
> +			return;
>  		overflow = false;
>  	} else if (overflow) {
> -		mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
> -				      cur_ctl &
> -				      ~(MSMON_CFG_x_CTL_OFLOW_STATUS |
> -					MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L));
> +		m->err = mpam_write_monsel_reg(msc, CFG_MBWU_CTL,
> +					    cur_ctl &
> +					    ~(MSMON_CFG_x_CTL_OFLOW_STATUS |
> +					    MSMON_CFG_MBWU_CTL_OFLOW_STATUS_L));
> +		if (m->err)
> +			return;
>  	}
>  
>  	switch (m->type) {
>  	case mpam_feat_msmon_csu:
> -		mpam_read_monsel_reg(msc, CSU, &now32);
> +		m->err = mpam_read_monsel_reg(msc, CSU, &now32);
> +		if (m->err)
> +			return;
>  		nrdy = now32 & MSMON___NRDY;
>  		now = FIELD_GET(MSMON___VALUE, now32);
>  
> @@ -1423,7 +1437,9 @@ static void __ris_msmon_read(void *arg)
>  			else
>  				now = FIELD_GET(MSMON___L_VALUE, now);
>  		} else {
> -			mpam_read_monsel_reg(msc, MBWU, &now32);
> +			m->err = mpam_read_monsel_reg(msc, MBWU, &now32);
> +			if (m->err)
> +				return;
>  			nrdy = now32 & MSMON___NRDY;
>  			now = FIELD_GET(MSMON___VALUE, now32);
>  		}
> @@ -1792,6 +1808,8 @@ static int mpam_restore_mbwu_state(void *_ris)
>  			mwbu_arg.val = &val;
>  
>  			__ris_msmon_read(&mwbu_arg);
> +			if (mwbu_arg.err)
> +				return mwbu_arg.err;

As sashiko points out [1], this is a change of behaviour as mbwu_arg.err could already be non-zero
previous to this patch. In particular, -EBUSY when NRDY is set. When this is the case we should
continue restoring the other counters rather than changing to bailing out early.

As -EBUSY is only used in the NRDY case you could change the condition to be:

if (mbwu_arg.err && mbwu_arg.err != -EBUSY)
         return mwbu_arg.err;

[1] https://sashiko.dev/#/patchset/20260729134124.2506269-1-andre.przywara%40arm.com

Thanks,

Ben

>  		}
>  	}
>