[PATCH v2 2/3] fs/resctrl: Assign counters to existing groups when enabling mbm_event

@@ -371,8 +371,11 @@ with the following files:
 	of counters available is described in the "num_mbm_cntrs" file. Changing the
 	mode may cause all counters on the resource to reset.
 
-	Moving to mbm_event counter assignment mode requires users to assign the counters
-	to the events. Otherwise, the MBM event counters will return 'Unassigned' when read.
+	Moving to mbm_event counter assignment mode enables "mbm_assign_on_mkdir" and
+	assigns counters to the events of all existing groups, including the default
+	group, for as long as counters remain available. Events left without a counter
+	will return 'Unassigned' when read until the user assigns one using
+	"mbm_L3_assignments".
 
 	The mode is beneficial for AMD platforms that support more CTRL_MON
 	and MON groups than available hardware counters. By default, this

@@ -1326,6 +1326,27 @@ void rdtgroup_assign_cntrs(struct rdtgroup *rdtgrp)
 					   &mon_event_all[QOS_L3_MBM_LOCAL_EVENT_ID]);
 }
 
+/*
+ * resctrl_assign_cntrs_allrdtgrp() - Assign counters to the MBM events of every
+ *				      existing group. Called when "mbm_event" mode
+ *				      is enabled.
+ *
+ * Groups created while in "default" mode have no counter assigned, including the
+ * default group created when resctrl is mounted. Assign counters to them so that
+ * enabling the mode leaves the same assignments that mkdir would have made.
+ */
+static void resctrl_assign_cntrs_allrdtgrp(void)
+{
+	struct rdtgroup *prgrp, *crgrp;
+
+	list_for_each_entry(prgrp, &rdt_all_groups, rdtgroup_list) {
+		rdtgroup_assign_cntrs(prgrp);
+
+		list_for_each_entry(crgrp, &prgrp->mon.crdtgrp_list, mon.crdtgrp_list)
+			rdtgroup_assign_cntrs(crgrp);
+	}
+}
+
 /*
  * rdtgroup_free_unassign_cntr() - Unassign and reset the counter ID configuration
  * for the event pointed to by @mevt within the domain @d and resctrl group @rdtgrp.

@@ -1599,9 +1620,6 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 									   (READS_TO_LOCAL_MEM |
 									    READS_TO_LOCAL_S_MEM |
 									    NON_TEMP_WRITE_TO_LOCAL_MEM);
-		/* Enable auto assignment when switching to "mbm_event" mode */
-		if (enable)
-			r->mon.mbm_assign_on_mkdir = true;
 		/*
 		 * Reset all the non-achitectural RMID state and assignable counters.
 		 */

@@ -1609,6 +1627,12 @@ ssize_t resctrl_mbm_assign_mode_write(struct kernfs_open_file *of, char *buf,
 			mbm_cntr_free_all(r, d);
 			resctrl_reset_rmid_all(r, d);
 		}
+
+		if (enable) {
+			/* Enable auto assignment when switching to "mbm_event" mode */
+			r->mon.mbm_assign_on_mkdir = true;
+			resctrl_assign_cntrs_allrdtgrp();
+		}
 	}
 
 out_unlock: