[PATCH v2 27/29] arm_mpam: Add helper to reset saved mbwu state

James Morse
2025-09-10T20:45:46Z

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>
---
drivers/resctrl/mpam_devices.c | 47 +++++++++++++++++++++++++++++++--
drivers/resctrl/mpam_internal.h | 5 +++-
2 files changed, 49 insertions(+), 3 deletions(-)

diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c
index 3080a81f0845..8254d6190ca2 100644
--- a/drivers/resctrl/mpam_devices.c
+++ b/drivers/resctrl/mpam_devices.c
@@ -1088,9 +1088,11 @@ static u64 mpam_msmon_overflow_val(struct mpam_msc_ris *ris)
static void __ris_msmon_read(void *arg)
{
bool nrdy = false;
+ bool config_mismatch;
struct mon_read *m = arg;
u64 now, overflow_val = 0;
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;
@@ -1105,6 +1107,14 @@ 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);

+ if (m->type == mpam_feat_msmon_mbwu) {
+ 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;
+ }
+ }
+
/*
* Read the existing configuration to avoid re-writing the same values.
* This saves waiting for 'nrdy' on subsequent reads.
@@ -1112,7 +1122,10 @@ static void __ris_msmon_read(void *arg)
read_msmon_ctl_flt_vals(m, &cur_ctl, &cur_flt);
clean_msmon_ctl_val(&cur_ctl);
gen_msmon_ctl_flt_vals(m, &ctl_val, &flt_val);
- if (cur_flt != flt_val || cur_ctl != (ctl_val | MSMON_CFG_x_CTL_EN))
+ config_mismatch = cur_flt != flt_val ||
+ 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);

switch (m->type) {
@@ -1145,7 +1158,6 @@ static void __ris_msmon_read(void *arg)
if (nrdy)
break;

- mbwu_state = &ris->mbwu_state[ctx->mon];
if (!mbwu_state)
break;

@@ -1245,6 +1257,37 @@ 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)
+{
+ int idx;
+ struct mpam_msc *msc;
+ struct mpam_vmsc *vmsc;
+ struct mpam_msc_ris *ris;
+
+ if (!mpam_is_enabled())
+ return;
+
+ idx = srcu_read_lock(&mpam_srcu);
+ list_for_each_entry_rcu(vmsc, &comp->vmsc, comp_list) {
+ if (!mpam_has_feature(mpam_feat_msmon_mbwu, &vmsc->props))
+ continue;
+
+ msc = vmsc->msc;
+ list_for_each_entry_rcu(ris, &vmsc->ris, vmsc_list) {
+ 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);
+ }
+ }
+ srcu_read_unlock(&mpam_srcu, idx);
+}
+
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 c190826dfbda..7cbcafe8294a 100644
--- a/drivers/resctrl/mpam_internal.h
+++ b/drivers/resctrl/mpam_internal.h
@@ -223,10 +223,12 @@ struct mon_cfg {

/*
* 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.
+ * Changes to reset_on_next_read, prev_val and correction are protected by the
+ * msc's mon_sel_lock.
*/
struct msmon_mbwu_state {
bool enabled;
+ bool reset_on_next_read;
struct mon_cfg cfg;

/* The value last read from the hardware. Used to detect overflow. */
@@ -393,6 +395,7 @@ 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);
--
2.39.5