arm_mpam: Add helper to reset saved mbwu state

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 <[e-mail]>
Cc: Peter Newman <[e-mail]>
Reviewed-by: Fenghua Yu <[e-mail]>
Reviewed-by: Gavin Shan <[e-mail]>
Reviewed-by: Jonathan Cameron <[e-mail]>
Reviewed-by: Shaopeng Tan <[e-mail]>
Tested-by: Fenghua Yu <[e-mail]>
Tested-by: Carl Worth <[e-mail]>
Tested-by: Gavin Shan <[e-mail]>
Tested-by: Zeng Heng <[e-mail]>
Tested-by: Shaopeng Tan <[e-mail]>
Tested-by: Hanjun Guo <[e-mail]>
Signed-off-by: Ben Horgan <[e-mail]>
Signed-off-by: Catalin Marinas <[e-mail]>

drivers/resctrl/mpam_devices.c

···
 	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;
···
 	mon_sel = FIELD_PREP(MSMON_CFG_MON_SEL_MON_SEL, ctx->mon) |
 		  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.
···
 	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) {
···
 	}
 
 	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)

drivers/resctrl/mpam_internal.h

···
 /* 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;
 
 	/*
···
 
 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);