[PATCH v2 24/29] arm_mpam: Track bandwidth counter state for overflow and power management

James Morse
2025-09-10T20:45:31Z

Bandwidth counters need to run continuously to correctly reflect the
bandwidth.

The value read may be lower than the previous value read in the case
of overflow and when the hardware is reset due to CPU hotplug.

Add struct mbwu_state to track the bandwidth counter to allow overflow
and power management to be handled.

Signed-off-by: James Morse <james.morse@arm.com>
---
Changes since v1:
* Fixed lock/unlock typo.
---
drivers/resctrl/mpam_devices.c | 154 +++++++++++++++++++++++++++++++-
drivers/resctrl/mpam_internal.h | 23 +++++
2 files changed, 175 insertions(+), 2 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 1543c33c5d6a..eeb62ed94520 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -918,6 +918,7 @@ static void gen_msmon_ctl_flt_vals(struct mon_read *m, u32 *ctl_val,
*ctl_val |= MSMON_CFG_x_CTL_MATCH_PARTID;

*flt_val = FIELD_PREP(MSMON_CFG_x_FLT_PARTID, ctx->partid);
+
if (m->ctx->match_pmg) {
*ctl_val |= MSMON_CFG_x_CTL_MATCH_PMG;
*flt_val |= FIELD_PREP(MSMON_CFG_x_FLT_PMG, ctx->pmg);
@@ -972,6 +973,7 @@ static void clean_msmon_ctl_val(u32 *cur_ctl)
static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
u32 flt_val)
{
+ struct msmon_mbwu_state *mbwu_state;
struct mpam_msc *msc = m->ris->vmsc->msc;

/*
@@ -990,20 +992,32 @@ static void write_msmon_ctl_flt_vals(struct mon_read *m, u32 ctl_val,
mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val);
mpam_write_monsel_reg(msc, MBWU, 0);
mpam_write_monsel_reg(msc, CFG_MBWU_CTL, ctl_val | MSMON_CFG_x_CTL_EN);
+
+ mbwu_state = &m->ris->mbwu_state[m->ctx->mon];
+ if (mbwu_state)
+ mbwu_state->prev_val = 0;
+
break;
default:
return;
}
}

+static u64 mpam_msmon_overflow_val(struct mpam_msc_ris *ris)
+{
+ /* TODO: scaling, and long counters */
+ return GENMASK_ULL(30, 0);
+}
+
/* Call with MSC lock held */
static void __ris_msmon_read(void *arg)
{
- u64 now;
bool nrdy = false;
struct mon_read *m = arg;
+ u64 now, overflow_val = 0;
struct mon_cfg *ctx = m->ctx;
struct mpam_msc_ris *ris = m->ris;
+ struct msmon_mbwu_state *mbwu_state;
struct mpam_props *rprops = &ris->props;
struct mpam_msc *msc = m->ris->vmsc->msc;
u32 mon_sel, ctl_val, flt_val, cur_ctl, cur_flt;
@@ -1031,11 +1045,30 @@ static void __ris_msmon_read(void *arg)
now = mpam_read_monsel_reg(msc, CSU);
if (mpam_has_feature(mpam_feat_msmon_csu_hw_nrdy, rprops))
nrdy = now & MSMON___NRDY;
+ now = FIELD_GET(MSMON___VALUE, now);
break;
case mpam_feat_msmon_mbwu:
now = mpam_read_monsel_reg(msc, MBWU);
if (mpam_has_feature(mpam_feat_msmon_mbwu_hw_nrdy, rprops))
nrdy = now & MSMON___NRDY;
+ now = FIELD_GET(MSMON___VALUE, now);
+
+ if (nrdy)
+ break;
+
+ mbwu_state = &ris->mbwu_state[ctx->mon];
+ if (!mbwu_state)
+ break;
+
+ /* Add any pre-overflow value to the mbwu_state->val */
+ if (mbwu_state->prev_val > now)
+ overflow_val = mpam_msmon_overflow_val(ris) - mbwu_state->prev_val;
+
+ mbwu_state->prev_val = now;
+ mbwu_state->correction += overflow_val;
+
+ /* Include bandwidth consumed before the last hardware reset */
+ now += mbwu_state->correction;
break;
default:
m->err = -EINVAL;
@@ -1048,7 +1081,6 @@ static void __ris_msmon_read(void *arg)
return;
}

- now = FIELD_GET(MSMON___VALUE, now);
*m->val += now;
}

@@ -1261,6 +1293,67 @@ static int mpam_reprogram_ris(void *_arg)
return 0;
}

+/* Call with MSC lock held */
+static int mpam_restore_mbwu_state(void *_ris)
+{
+ int i;
+ struct mon_read mwbu_arg;
+ struct mpam_msc_ris *ris = _ris;
+
+ for (i = 0; i < ris->props.num_mbwu_mon; i++) {
+ if (ris->mbwu_state[i].enabled) {
+ mwbu_arg.ris = ris;
+ mwbu_arg.ctx = &ris->mbwu_state[i].cfg;
+ mwbu_arg.type = mpam_feat_msmon_mbwu;
+
+ __ris_msmon_read(&mwbu_arg);
+ }
+ }
+
+ return 0;
+}
+
+/* Call with MSC lock and held */
+static int mpam_save_mbwu_state(void *arg)
+{
+ int i;
+ u64 val;
+ struct mon_cfg *cfg;
+ u32 cur_flt, cur_ctl, mon_sel;
+ struct mpam_msc_ris *ris = arg;
+ struct msmon_mbwu_state *mbwu_state;
+ struct mpam_msc *msc = ris->vmsc->msc;
+
+ for (i = 0; i < ris->props.num_mbwu_mon; i++) {
+ mbwu_state = &ris->mbwu_state[i];
+ cfg = &mbwu_state->cfg;
+
+ if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
+ return -EIO;
+
+ mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, i) |
+ FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
+ mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);
+
+ cur_flt = mpam_read_monsel_reg(msc, CFG_MBWU_FLT);
+ cur_ctl = mpam_read_monsel_reg(msc, CFG_MBWU_CTL);
+ mpam_write_monsel_reg(msc, CFG_MBWU_CTL, 0);
+
+ val = mpam_read_monsel_reg(msc, MBWU);
+ mpam_write_monsel_reg(msc, MBWU, 0);
+
+ cfg->mon = i;
+ cfg->pmg = FIELD_GET(MSMON_CFG_x_FLT_PMG, cur_flt);
+ cfg->match_pmg = FIELD_GET(MSMON_CFG_x_CTL_MATCH_PMG, cur_ctl);
+ 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;
+}
+
static void mpam_init_reset_cfg(struct mpam_config *reset_cfg)
{
memset(reset_cfg, 0, sizeof(*reset_cfg));
@@ -1335,6 +1428,9 @@ static void mpam_reset_msc(struct mpam_msc *msc, bool online)
* for non-zero partid may be lost while the CPUs are offline.
*/
ris->in_reset_state = online;
+
+ if (mpam_is_enabled() && !online)
+ mpam_touch_msc(msc, &mpam_save_mbwu_state, ris);
}
}

@@ -1369,6 +1465,9 @@ static void mpam_reprogram_msc(struct mpam_msc *msc)
mpam_reprogram_ris_partid(ris, partid, cfg);
}
ris->in_reset_state = reset;
+
+ if (mpam_has_feature(mpam_feat_msmon_mbwu, &ris->props))
+ mpam_touch_msc(msc, &mpam_restore_mbwu_state, ris);
}
}

@@ -2091,11 +2190,33 @@ static void mpam_unregister_irqs(void)

static void __destroy_component_cfg(struct mpam_component *comp)
{
+ struct mpam_msc *msc;
+ struct mpam_vmsc *vmsc;
+ struct mpam_msc_ris *ris;
+
+ lockdep_assert_held(&mpam_list_lock);
+
add_to_garbage(comp->cfg);
+ list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
+ msc = vmsc->msc;
+
+ if (mpam_mon_sel_lock(msc)) {
+ list_for_each_entry(ris, &vmsc->ris, vmsc_list)
+ add_to_garbage(ris->mbwu_state);
+ mpam_mon_sel_unlock(msc);
+ }
+ }
}

static int __allocate_component_cfg(struct mpam_component *comp)
{
+ int err = 0;
+ struct mpam_msc *msc;
+ struct mpam_vmsc *vmsc;
+ struct mpam_msc_ris *ris;
+ struct msmon_mbwu_state *mbwu_state;
+
+ lockdep_assert_held(&mpam_list_lock);
mpam_assert_partid_sizes_fixed();

if (comp->cfg)
@@ -2106,6 +2227,35 @@ static int __allocate_component_cfg(struct mpam_component *comp)
return -ENOMEM;
init_garbage(comp->cfg);

+ list_for_each_entry(vmsc, &comp->vmsc, comp_list) {
+ if (!vmsc->props.num_mbwu_mon)
+ continue;
+
+ msc = vmsc->msc;
+ list_for_each_entry(ris, &vmsc->ris, vmsc_list) {
+ if (!ris->props.num_mbwu_mon)
+ continue;
+
+ mbwu_state = kcalloc(ris->props.num_mbwu_mon,
+ sizeof(*ris->mbwu_state),
+ GFP_KERNEL);
+ if (!mbwu_state) {
+ __destroy_component_cfg(comp);
+ err = -ENOMEM;
+ break;
+ }
+
+ if (mpam_mon_sel_lock(msc)) {
+ init_garbage(mbwu_state);
+ ris->mbwu_state = mbwu_state;
+ mpam_mon_sel_unlock(msc);
+ }
+ }
+
+ if (err)
+ break;
+ }
+
return 0;
}

diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index bb01e7dbde40..725c2aefa8a2 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -212,6 +212,26 @@ struct mon_cfg {
enum mon_filter_options opts;
};

+/*
+ * Changes to enabled and cfg are protected by the msc->lock.
+ * Changes to prev_val and correction are protected by the msc's mon_sel_lock.
+ */
+struct msmon_mbwu_state {
+ bool enabled;
+ struct mon_cfg cfg;
+
+ /* The value last read from the hardware. Used to detect overflow. */
+ u64 prev_val;
+
+ /*
+ * The value to add to the new reading to account for power management,
+ * and shifts to trigger the overflow interrupt.
+ */
+ u64 correction;
+
+ struct mpam_garbage garbage;
+};
+
struct mpam_class {
/* mpam_components in this class */
struct list_head components;
@@ -304,6 +324,9 @@ struct mpam_msc_ris {
/* parent: */
struct mpam_vmsc *vmsc;

+ /* msmon mbwu configuration is preserved over reset */
+ struct msmon_mbwu_state *mbwu_state;
+
struct mpam_garbage garbage;
};

--
2.39.5