[PATCH] arm_mpam: Only program MATCH_PMG when the monitor supports it

[Ben Horgan]

Hi Ping,

On 02/11/2026 07:13, Ping Li wrote:
> An MSC of ours implements the MBWU monitor without PMG support:
> MPAMF_MBWUMON_IDR.NO_MATCH_PMG is 1, so MSMON_CFG_x_CTL.MATCH_PMG is
> RES0. On this hardware resctrl monitor reads always returned 0.
> 
> Tracking this down: __read_mon() unconditionally sets match_pmg,
> because the resctrl (closid, rmid) model maps rmid to PMG. The
> expected configuration generated by gen_msmon_ctl_flt_vals() then
> contains MATCH_PMG, but the hardware ignores the bit, so the
> configuration read back never matches, config_mismatch is always
> true and the monitor is reprogrammed on every read - the counter
> never accumulates.
> 
> The architecture allows an MSMON implementation without PMG
> support, so read the NO_MATCH_PMG bits during probe and only
> program MATCH_PMG when the monitor supports PMG filtering,
> falling back to filtering by PARTID only. The CSU monitor has
> the same issue and is covered the same way.

I'm afraid this doesn't work. resctrl will show the same counts for every monitor group under a
control group rather than the counts related to the tasks/cpus associated with the individual
monitor groups.

Have you actually built NO_MATCH_PMG? I ask because I understood that NO_MATCH_PMG and
NO_MATCH_PARTID were erroneously added to the MPAMv1 specification and were going to be removed.
What you should build or not is question for support at arm.com rather than the list though.

Thanks,

Ben

> 
> Signed-off-by: Ping Li <leeonion.muyu at gmail.com>
> ---
>  drivers/resctrl/mpam_devices.c  | 22 +++++++++++++++++++++-
>  drivers/resctrl/mpam_internal.h |  4 ++++
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
> index c067b6d57d71..2086ff121b59 100644
> --- a/drivers/resctrl/mpam_devices.c
> +++ b/drivers/resctrl/mpam_devices.c
> @@ -1089,6 +1089,9 @@ static int mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>  				if (FIELD_GET(MPAMF_CSUMON_IDR_HAS_XCL, csumonidr))
>  					mpam_set_feature(mpam_feat_msmon_csu_xcl, props);
>  
> +				if (!FIELD_GET(MPAMF_CSUMON_IDR_NO_MATCH_PMG, csumonidr))
> +					mpam_set_feature(mpam_feat_msmon_csu_match_pmg, props);
> +
>  				/* Is NRDY hardware managed? */
>  				err = mpam_ris_hw_probe_csu_nrdy(ris);
>  				if (err < 0)
> @@ -1118,6 +1121,9 @@ static int mpam_ris_hw_probe(struct mpam_msc_ris *ris)
>  				if (FIELD_GET(MPAMF_MBWUMON_IDR_HAS_RWBW, mbwumon_idr))
>  					mpam_set_feature(mpam_feat_msmon_mbwu_rwbw, props);
>  
> +				if (!FIELD_GET(MPAMF_MBWUMON_IDR_NO_MATCH_PMG, mbwumon_idr))
> +					mpam_set_feature(mpam_feat_msmon_mbwu_match_pmg, props);
> +
>  				has_long = FIELD_GET(MPAMF_MBWUMON_IDR_HAS_LONG, mbwumon_idr);
>  				if (has_long) {
>  					if (FIELD_GET(MPAMF_MBWUMON_IDR_LWD, mbwumon_idr))
> @@ -1309,6 +1315,20 @@ static int mpam_msc_zero_mbwu_l(struct mpam_msc *msc)
>  	return __mpam_write_reg(msc, MSMON_MBWU_L + 4, 0);
>  }
>  
> +static bool msmon_supports_match_pmg(struct mon_read *m)
> +{
> +	switch (m->type) {
> +	case mpam_feat_msmon_csu:
> +		return mpam_has_feature(mpam_feat_msmon_csu_match_pmg, &m->ris->props);
> +	case mpam_feat_msmon_mbwu_31counter:
> +	case mpam_feat_msmon_mbwu_44counter:
> +	case mpam_feat_msmon_mbwu_63counter:
> +		return mpam_has_feature(mpam_feat_msmon_mbwu_match_pmg, &m->ris->props);
> +	default:
> +		return true;
> +	}
> +}
> +
>  static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
>  				   u32 *flt_val)
>  {
> @@ -1322,7 +1342,7 @@ static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
>  
>  	*flt_val = FIELD_PREP(MSMON_CFG_x_FLT_PARTID, ctx->partid);
>  
> -	if (m->ctx->match_pmg) {
> +	if (m->ctx->match_pmg && msmon_supports_match_pmg(m)) {
>  		*ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
>  		*flt_val |= FIELD_PREP(MSMON_CFG_x_FLT_PMG, ctx->pmg);
>  	}
> diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
> index 1f86cc158100..88cd5ac4cde3 100644
> --- a/drivers/resctrl/mpam_internal.h
> +++ b/drivers/resctrl/mpam_internal.h
> @@ -227,12 +227,14 @@ enum mpam_device_features {
>  	mpam_feat_msmon_csu,
>  	mpam_feat_msmon_csu_capture,
>  	mpam_feat_msmon_csu_xcl,
> +	mpam_feat_msmon_csu_match_pmg,
>  	mpam_feat_msmon_mbwu,
>  	mpam_feat_msmon_mbwu_31counter,
>  	mpam_feat_msmon_mbwu_44counter,
>  	mpam_feat_msmon_mbwu_63counter,
>  	mpam_feat_msmon_mbwu_capture,
>  	mpam_feat_msmon_mbwu_rwbw,
> +	mpam_feat_msmon_mbwu_match_pmg,
>  	mpam_feat_partid_nrw,
>  	MPAM_FEATURE_LAST
>  };
> @@ -645,6 +647,7 @@ int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc);
>  
>  /* MPAMF_CSUMON_IDR - MPAM cache storage usage monitor ID register */
>  #define MPAMF_CSUMON_IDR_NUM_MON	GENMASK(15, 0)
> +#define MPAMF_CSUMON_IDR_NO_MATCH_PMG	BIT(22)
>  #define MPAMF_CSUMON_IDR_HAS_OFLOW_CAPT	BIT(24)
>  #define MPAMF_CSUMON_IDR_HAS_CEVNT_OFLW	BIT(25)
>  #define MPAMF_CSUMON_IDR_HAS_OFSR	BIT(26)
> @@ -655,6 +658,7 @@ int mpam_fb_check_shared_buffer_size(struct mpam_msc *msc);
>  
>  /* MPAMF_MBWUMON_IDR - MPAM memory bandwidth usage monitor ID register */
>  #define MPAMF_MBWUMON_IDR_NUM_MON	GENMASK(15, 0)
> +#define MPAMF_MBWUMON_IDR_NO_MATCH_PMG	BIT(22)
>  #define MPAMF_MBWUMON_IDR_HAS_RWBW	BIT(28)
>  #define MPAMF_MBWUMON_IDR_LWD		BIT(29)
>  #define MPAMF_MBWUMON_IDR_HAS_LONG	BIT(30)