fs/resctrl: Introduce mbm_assign_on_mkdir to enable assignments on mkdir

The "mbm_event" counter assignment mode allows users to assign a hardware
counter to an RMID, event pair and monitor the bandwidth as long as it is
assigned.

Introduce a user-configurable option that determines if a counter will
automatically be assigned to an RMID, event pair when its associated
monitor group is created via mkdir. Accessible when "mbm_event" counter
assignment mode is enabled.

Suggested-by: Peter Newman <peternewman@google.com>
Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/cover.1757108044.git.babu.moger@amd.com

Documentation/filesystems/resctrl.rst

@@ -355,6 +355,26 @@ with the following files:
 	  # cat /sys/fs/resctrl/info/L3_MON/event_configs/mbm_total_bytes/event_filter
 	   local_reads,local_non_temporal_writes
 
+"mbm_assign_on_mkdir":
+	Exists when "mbm_event" counter assignment mode is supported. Accessible
+	only when "mbm_event" counter assignment mode is enabled.
+
+	Determines if a counter will automatically be assigned to an RMID, MBM event
+	pair when its associated monitor group is created via mkdir. Enabled by default
+	on boot, also when switched from "default" mode to "mbm_event" counter assignment
+	mode. Users can disable this capability by writing to the interface.
+
+	"0":
+		Auto assignment is disabled.
+	"1":
+		Auto assignment is enabled.
+
+	Example::
+
+	  # echo 0 > /sys/fs/resctrl/info/L3_MON/mbm_assign_on_mkdir
+	  # cat /sys/fs/resctrl/info/L3_MON/mbm_assign_on_mkdir
+	  0
+
 "max_threshold_occupancy":
 		Read/write file provides the largest value (in
 		bytes) at which a previously used LLC_occupancy

fs/resctrl/internal.h

@@ -410,6 +410,12 @@ int event_filter_show(struct kernfs_open_file *of, struct seq_file *seq, void *v
 ssize_t event_filter_write(struct kernfs_open_file *of, char *buf, size_t nbytes,
 			   loff_t off);
 
+int resctrl_mbm_assign_on_mkdir_show(struct kernfs_open_file *of,
+				     struct seq_file *s, void *v);
+
+ssize_t resctrl_mbm_assign_on_mkdir_write(struct kernfs_open_file *of, char *buf,
+					  size_t nbytes, loff_t off);
+
 #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
 int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
 

fs/resctrl/monitor.c

@@ -1027,6 +1027,57 @@ out_unlock:
 	return ret;
 }
 
+int resctrl_mbm_assign_on_mkdir_show(struct kernfs_open_file *of, struct seq_file *s,
+				     void *v)
+{
+	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
+	int ret = 0;
+
+	mutex_lock(&rdtgroup_mutex);
+	rdt_last_cmd_clear();
+
+	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		rdt_last_cmd_puts("mbm_event counter assignment mode is not enabled\n");
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	seq_printf(s, "%u\n", r->mon.mbm_assign_on_mkdir);
+
+out_unlock:
+	mutex_unlock(&rdtgroup_mutex);
+
+	return ret;
+}
+
+ssize_t resctrl_mbm_assign_on_mkdir_write(struct kernfs_open_file *of, char *buf,
+					  size_t nbytes, loff_t off)
+{
+	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
+	bool value;
+	int ret;
+
+	ret = kstrtobool(buf, &value);
+	if (ret)
+		return ret;
+
+	mutex_lock(&rdtgroup_mutex);
+	rdt_last_cmd_clear();
+
+	if (!resctrl_arch_mbm_cntr_assign_enabled(r)) {
+		rdt_last_cmd_puts("mbm_event counter assignment mode is not enabled\n");
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	r->mon.mbm_assign_on_mkdir = value;
+
+out_unlock:
+	mutex_unlock(&rdtgroup_mutex);
+
+	return ret ?: nbytes;
+}
+
 /*
  * rdtgroup_assign_cntr() - Assign/unassign the counter ID for the event, RMID
  * pair in the domain.
@@ -1457,6 +1508,8 @@ int resctrl_mon_resource_init(void)
 		resctrl_file_fflags_init("available_mbm_cntrs",
 					 RFTYPE_MON_INFO | RFTYPE_RES_CACHE);
 		resctrl_file_fflags_init("event_filter", RFTYPE_ASSIGN_CONFIG);
+		resctrl_file_fflags_init("mbm_assign_on_mkdir", RFTYPE_MON_INFO |
+					 RFTYPE_RES_CACHE);
 	}
 
 	return 0;

fs/resctrl/rdtgroup.c

@@ -1808,6 +1808,13 @@ static struct rftype res_common_files[] = {
 		.seq_show	= rdt_last_cmd_status_show,
 		.fflags		= RFTYPE_TOP_INFO,
 	},
+	{
+		.name		= "mbm_assign_on_mkdir",
+		.mode		= 0644,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= resctrl_mbm_assign_on_mkdir_show,
+		.write		= resctrl_mbm_assign_on_mkdir_write,
+	},
 	{
 		.name		= "num_closids",
 		.mode		= 0444,

include/linux/resctrl.h

@@ -277,12 +277,15 @@ enum resctrl_schema_fmt {
  *			monitoring events can be configured.
  * @num_mbm_cntrs:	Number of assignable counters.
  * @mbm_cntr_assignable:Is system capable of supporting counter assignment?
+ * @mbm_assign_on_mkdir:True if counters should automatically be assigned to MBM
+ *			events of monitor groups created via mkdir.
  */
 struct resctrl_mon {
 	int			num_rmid;
 	unsigned int		mbm_cfg_mask;
 	int			num_mbm_cntrs;
 	bool			mbm_cntr_assignable;
+	bool			mbm_assign_on_mkdir;
 };
 
 /**