x86/resctrl: Create Sub-NUMA Cluster (SNC) monitor files

When SNC mode is enabled, create subdirectories and files to monitor at the SNC
node granularity. Legacy behavior is preserved by tagging the monitor files at
the L3 granularity with the "sum" attribute.  When the user reads these files
the kernel will read monitor data from all SNC nodes that share the same L3
cache instance and return the aggregated value to the user.

Note that the "domid" field for files that must sum across SNC domains has the
L3 cache instance id, while non-summing files use the domain id.

The "sum" files do not need to make a call to mon_event_read() to initialize
the MBM counters. This will be handled by initializing the individual SNC nodes
that share the L3.
Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20240628215619.76401-14-tony.luck@intel.com

arch/x86/kernel/cpu/resctrl/rdtgroup.c

@@ -3026,7 +3026,8 @@ static void rmdir_mondata_subdir_allrdtgrp(struct rdt_resource *r,
 }
 
 static int mon_add_all_files(struct kernfs_node *kn, struct rdt_mon_domain *d,
-			     struct rdt_resource *r, struct rdtgroup *prgrp)
+			     struct rdt_resource *r, struct rdtgroup *prgrp,
+			     bool do_sum)
 {
 	struct rmid_read rr = {0};
 	union mon_data_bits priv;
@@ -3037,14 +3038,15 @@ static int mon_add_all_files(struct kernfs_node *kn, struct rdt_mon_domain *d,
 		return -EPERM;
 
 	priv.u.rid = r->rid;
-	priv.u.domid = d->hdr.id;
+	priv.u.domid = do_sum ? d->ci->id : d->hdr.id;
+	priv.u.sum = do_sum;
 	list_for_each_entry(mevt, &r->evt_list, list) {
 		priv.u.evtid = mevt->evtid;
 		ret = mon_addfile(kn, mevt->name, priv.priv);
 		if (ret)
 			return ret;
 
-		if (is_mbm_event(mevt->evtid))
+		if (!do_sum && is_mbm_event(mevt->evtid))
 			mon_event_read(&rr, r, d, prgrp, mevt->evtid, true);
 	}
 
@@ -3055,23 +3057,51 @@ static int mkdir_mondata_subdir(struct kernfs_node *parent_kn,
 				struct rdt_mon_domain *d,
 				struct rdt_resource *r, struct rdtgroup *prgrp)
 {
-	struct kernfs_node *kn;
+	struct kernfs_node *kn, *ckn;
 	char name[32];
-	int ret;
+	bool snc_mode;
+	int ret = 0;
 
-	sprintf(name, "mon_%s_%02d", r->name, d->hdr.id);
-	/* create the directory */
-	kn = kernfs_create_dir(parent_kn, name, parent_kn->mode, prgrp);
-	if (IS_ERR(kn))
-		return PTR_ERR(kn);
+	lockdep_assert_held(&rdtgroup_mutex);
 
-	ret = rdtgroup_kn_set_ugid(kn);
-	if (ret)
-		goto out_destroy;
+	snc_mode = r->mon_scope == RESCTRL_L3_NODE;
+	sprintf(name, "mon_%s_%02d", r->name, snc_mode ? d->ci->id : d->hdr.id);
+	kn = kernfs_find_and_get(parent_kn, name);
+	if (kn) {
+		/*
+		 * rdtgroup_mutex will prevent this directory from being
+		 * removed. No need to keep this hold.
+		 */
+		kernfs_put(kn);
+	} else {
+		kn = kernfs_create_dir(parent_kn, name, parent_kn->mode, prgrp);
+		if (IS_ERR(kn))
+			return PTR_ERR(kn);
 
-	ret = mon_add_all_files(kn, d, r, prgrp);
-	if (ret)
-		goto out_destroy;
+		ret = rdtgroup_kn_set_ugid(kn);
+		if (ret)
+			goto out_destroy;
+		ret = mon_add_all_files(kn, d, r, prgrp, snc_mode);
+		if (ret)
+			goto out_destroy;
+	}
+
+	if (snc_mode) {
+		sprintf(name, "mon_sub_%s_%02d", r->name, d->hdr.id);
+		ckn = kernfs_create_dir(kn, name, parent_kn->mode, prgrp);
+		if (IS_ERR(ckn)) {
+			ret = -EINVAL;
+			goto out_destroy;
+		}
+
+		ret = rdtgroup_kn_set_ugid(ckn);
+		if (ret)
+			goto out_destroy;
+
+		ret = mon_add_all_files(ckn, d, r, prgrp, false);
+		if (ret)
+			goto out_destroy;
+	}
 
 	kernfs_activate(kn);
 	return 0;