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

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Message-ID: <20251107123450.664001-32-ben.horgan@arm.com>
Date: Fri,  7 Nov 2025 12:34:48 +0000
From: Ben Horgan <ben.horgan@....com>
To: james.morse@....com
Cc: amitsinght@...vell.com,
	baisheng.gao@...soc.com,
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	Fenghua Yu <fenghuay@...ia.com>,
	Ben Horgan <ben.horgan@....com>
Subject: [PATCH 31/33] arm_mpam: Add helper to reset saved mbwu state

From: James Morse <james.morse@....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@....com>
Reviewed-by: Fenghua Yu <fenghuay@...ia.com>
Tested-by: Fenghua Yu <fenghuay@...dia.com>
Cc: Peter Newman <peternewman@...gle.com>
Signed-off-by: Ben Horgan <ben.horgan@....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