fs/resctrl: Introduce the interface to display monitoring modes

Introduce the resctrl file "mbm_assign_mode" to list the supported counter
assignment modes.

The "mbm_event" counter assignment mode allows users to assign a hardware
counter to an RMID, event pair and monitor bandwidth usage as long as it is
assigned. The hardware continues to track the assigned counter until it is
explicitly unassigned by the user. Each event within a resctrl group can be
assigned independently in this mode.

On AMD systems "mbm_event" mode is backed by the ABMC (Assignable Bandwidth
Monitoring Counters) hardware feature and is enabled by default.

The "default" mode is the existing mode that works without the explicit
counter assignment, instead relying on dynamic counter assignment by hardware
that may result in hardware not dedicating a counter resulting in monitoring
data reads returning "Unavailable".

Provide an interface to display the monitor modes on the system.

  $ cat /sys/fs/resctrl/info/L3_MON/mbm_assign_mode
  [mbm_event]
  default

Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check to support Arm64.

On x86, CONFIG_RESCTRL_ASSIGN_FIXED is not defined. On Arm64, it will be
defined when the "mbm_event" mode is supported.

Add IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED) check early to ensure the user
interface remains compatible with upcoming Arm64 support. IS_ENABLED() safely
evaluates to 0 when the configuration is not defined.

As a result, for MPAM, the display would be either:

  [default]

or

  [mbm_event]

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

3 files changed, 42 insertions, 1 deletions

diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 7a57366d1abc..78aeb7ea38af 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -382,6 +382,10 @@ bool closid_allocated(unsigned int closid);
 
 int resctrl_find_cleanest_closid(void);
 
+void *rdt_kn_parent_priv(struct kernfs_node *kn);
+
+int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of, struct seq_file *s, void *v);
+
 #ifdef CONFIG_RESCTRL_FS_PSEUDO_LOCK
 int rdtgroup_locksetup_enter(struct rdtgroup *rdtgrp);
 
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index b578451de2b5..96231d517e71 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -882,6 +882,36 @@ bool resctrl_is_mon_event_enabled(enum resctrl_event_id eventid)
 	       mon_event_all[eventid].enabled;
 }
 
+int resctrl_mbm_assign_mode_show(struct kernfs_open_file *of,
+				 struct seq_file *s, void *v)
+{
+	struct rdt_resource *r = rdt_kn_parent_priv(of->kn);
+	bool enabled;
+
+	mutex_lock(&rdtgroup_mutex);
+	enabled = resctrl_arch_mbm_cntr_assign_enabled(r);
+
+	if (r->mon.mbm_cntr_assignable) {
+		if (enabled)
+			seq_puts(s, "[mbm_event]\n");
+		else
+			seq_puts(s, "[default]\n");
+
+		if (!IS_ENABLED(CONFIG_RESCTRL_ASSIGN_FIXED)) {
+			if (enabled)
+				seq_puts(s, "default\n");
+			else
+				seq_puts(s, "mbm_event\n");
+		}
+	} else {
+		seq_puts(s, "[default]\n");
+	}
+
+	mutex_unlock(&rdtgroup_mutex);
+
+	return 0;
+}
+
 /**
  * resctrl_mon_resource_init() - Initialise global monitoring structures.
  *
diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
index b6ab10704993..144585a85996 100644
--- a/fs/resctrl/rdtgroup.c
+++ b/fs/resctrl/rdtgroup.c
@@ -975,7 +975,7 @@ static int rdt_last_cmd_status_show(struct kernfs_open_file *of,
 	return 0;
 }
 
-static void *rdt_kn_parent_priv(struct kernfs_node *kn)
+void *rdt_kn_parent_priv(struct kernfs_node *kn)
 {
 	/*
 	 * The parent pointer is only valid within RCU section since it can be
@@ -1912,6 +1912,13 @@ static struct rftype res_common_files[] = {
 		.write		= mbm_local_bytes_config_write,
 	},
 	{
+		.name		= "mbm_assign_mode",
+		.mode		= 0444,
+		.kf_ops		= &rdtgroup_kf_single_ops,
+		.seq_show	= resctrl_mbm_assign_mode_show,
+		.fflags		= RFTYPE_MON_INFO | RFTYPE_RES_CACHE,
+	},
+	{
 		.name		= "cpus",
 		.mode		= 0644,
 		.kf_ops		= &rdtgroup_kf_single_ops,