[PATCH 31/33] arm_mpam: Add helper to reset saved mbwu state

Ben Horgan
2025-11-07T12:38:10Z

From: James Morse <james.morse@arm.com>

resctrl expects to reset the bandwidth counters when the filesystem
is mounted.

To allow this, add a helper that clears the saved mbwu state. Instead
of cross calling to each CPU that can access the component MSC to
write to the counter, set a flag that causes it to be zero'd on the
the next read. This is easily done by forcing a configuration update.

Signed-off-by: James Morse <james.morse@arm.com>
Reviewed-by: Fenghua Yu <fenghuay@nvdia.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Cc: Peter Newman <peternewman@google.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
---
Changes since v3:
Correct type checking, use mpam_feat_msmon_mbwu_<n>counter
---
drivers/resctrl/mpam_devices.c | 48 ++++++++++++++++++++++++++++++++-
drivers/resctrl/mpam_internal.h | 2 ++
2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 59d12ee1195d..eb6417f57e23 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1075,6 +1075,7 @@ static void __ris_msmon_read(void *arg)
bool overflow;
struct mon_read *m = arg;
struct mon_cfg *ctx = m->ctx;
+ bool reset_on_next_read = false;
struct mpam_msc_ris *ris = m->ris;
struct msmon_mbwu_state *mbwu_state;
struct mpam_props *rprops = &ris->props;
@@ -1089,6 +1090,20 @@ static void __ris_msmon_read(void *arg)
FIELD_PREP(MSMON_CFG_MON_SEL_RIS, ris->ris_idx);
mpam_write_monsel_reg(msc, CFG_MON_SEL, mon_sel);

+ switch (m->type) {
+ case mpam_feat_msmon_mbwu_31counter:
+ case mpam_feat_msmon_mbwu_44counter:
+ case mpam_feat_msmon_mbwu_63counter:
+ mbwu_state = &ris->mbwu_state[ctx->mon];
+ if (mbwu_state) {
+ reset_on_next_read = mbwu_state->reset_on_next_read;
+ mbwu_state->reset_on_next_read = false;
+ }
+ break;
+ default:
+ break;
+ }
+
/*
* Read the existing configuration to avoid re-writing the same values.
* This saves waiting for 'nrdy' on subsequent reads.
@@ -1106,7 +1121,7 @@ static void __ris_msmon_read(void *arg)
config_mismatch = cur_flt != flt_val ||
cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN);

- if (config_mismatch) {
+ if (config_mismatch || reset_on_next_read) {
write_msmon_ctl_flt_vals(m, ctl_val, flt_val);
overflow = false;
} else if (overflow) {
@@ -1264,6 +1279,37 @@ int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
return err;
}

+void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct mon_cfg *ctx)
+{
+ struct mpam_msc *msc;
+ struct mpam_vmsc *vmsc;
+ struct mpam_msc_ris *ris;
+
+ if (!mpam_is_enabled())
+ return;
+
+ guard(srcu)(&mpam_srcu);
+ list_for_each_entry_srcu(vmsc, &comp->vmsc, comp_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ if (!mpam_has_feature(mpam_feat_msmon_mbwu, &vmsc->props))
+ continue;
+
+ msc = vmsc->msc;
+ list_for_each_entry_srcu(ris, &vmsc->ris, vmsc_list,
+ srcu_read_lock_held(&mpam_srcu)) {
+ if (!mpam_has_feature(mpam_feat_msmon_mbwu, &ris->props))
+ continue;
+
+ if (WARN_ON_ONCE(!mpam_mon_sel_lock(msc)))
+ continue;
+
+ ris->mbwu_state[ctx->mon].correction = 0;
+ ris->mbwu_state[ctx->mon].reset_on_next_read = true;
+ mpam_mon_sel_unlock(msc);
+ }
+ }
+}
+
static void mpam_reset_msc_bitmap(struct mpam_msc *msc, u16 reg, u16 wd)
{
u32 num_words, msb;
diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h
index f3bf26b7fdaf..0061d355ad3e 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -209,6 +209,7 @@ struct mon_cfg {
/* Changes to msmon_mbwu_state are protected by the msc's mon_sel_lock. */
struct msmon_mbwu_state {
bool enabled;
+ bool reset_on_next_read;
struct mon_cfg cfg;

/*
@@ -368,6 +369,7 @@ int mpam_apply_config(struct mpam_component *comp, u16 partid,

int mpam_msmon_read(struct mpam_component *comp, struct mon_cfg *ctx,
enum mpam_device_features, u64 *val);
+void mpam_msmon_reset_mbwu(struct mpam_component *comp, struct mon_cfg *ctx);

int mpam_get_cpumask_from_cache_id(unsigned long cache_id, u32 cache_level,
cpumask_t *affinity);
--
2.43.0