[PATCH v14 20/32] fs/resctrl: Report 'Unassigned' for MBM events in mbm_event mode

[Babu Moger]

When "mbm_event" mode is enabled, a hardware counter must be assigned to
read the event.

Report 'Unassigned' in case the user attempts to read the event without
assigning a hardware counter.

Export mbm_cntr_get() to allow usage from other functions within
fs/resctrl.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
v14: Updated the changelog.
     Added the code comment for "-ENOENT" when counter is read without assignement.
     Removed the references to resctrl_is_mbm_event().

v13: Minor commitlog and user doc update.
     Resolved conflicts caused by the recent FS/ARCH code restructure.
     The monitor.c/rdtgroup.c files have been split between the FS and ARCH directories.

v12: Updated the documentation for more clarity.

v11: Domain can be NULL with SNC support so moved the unassign check in
     rdtgroup_mondata_show().

v10: Moved the code to check the assign state inside mon_event_read().
     Fixed few text comments.

v9: Used is_mbm_event() to check the event type.
    Minor user documentation update.

v8: Used MBM_EVENT_ARRAY_INDEX to get the index for the MBM event.
    Documentation update to make the text generic.

v7: Moved the documentation under "mon_data".
    Updated the text little bit.

v6: Added more explaination in the resctrl.rst
    Added checks to detect "Unassigned" before reading RMID.

v5: New patch.
---
 Documentation/filesystems/resctrl.rst |  8 ++++++++
 fs/resctrl/ctrlmondata.c              | 19 ++++++++++++++++++-
 fs/resctrl/internal.h                 |  2 ++
 fs/resctrl/monitor.c                  |  4 ++--
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/Documentation/filesystems/resctrl.rst b/Documentation/filesystems/resctrl.rst
index 8a2050098091..18de335e1ff8 100644
--- a/Documentation/filesystems/resctrl.rst
+++ b/Documentation/filesystems/resctrl.rst
@@ -434,6 +434,14 @@ When monitoring is enabled all MON groups will also contain:
 	for the L3 cache they occupy). These are named "mon_sub_L3_YY"
 	where "YY" is the node number.
 
+	The "mbm_event" mode offers "num_mbm_cntrs" number of counters and
+	allows users to assign counter IDs to mon_hw_id, event pairs enabling
+	bandwidth monitoring for as long as the counter remains assigned. The
+	hardware will continue tracking the assigned mon_hw_id until the user
+	manually unassigns it, ensuring that event data is not reset during this
+	period. An MBM event returns 'Unassigned' when the event does not have
+	a hardware counter assigned.
+
 "mon_hw_id":
 	Available only with debug option. The identifier used by hardware
 	for the monitor group. On x86 this is the RMID.
diff --git a/fs/resctrl/ctrlmondata.c b/fs/resctrl/ctrlmondata.c
index ad7ffc6acf13..8a182f506877 100644
--- a/fs/resctrl/ctrlmondata.c
+++ b/fs/resctrl/ctrlmondata.c
@@ -648,15 +648,32 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 			goto out;
 		}
 		d = container_of(hdr, struct rdt_mon_domain, hdr);
+
+		/*
+		 * Report 'Unassigned' if "mbm_event" mode is enabled and counter
+		 * is unassigned.
+		 */
+		if (resctrl_arch_mbm_cntr_assign_enabled(r) &&
+		    resctrl_is_mbm_event(evtid) &&
+		    (mbm_cntr_get(r, d, rdtgrp, evtid) < 0)) {
+			rr.err = -ENOENT;
+			goto checkresult;
+		}
+
 		mon_event_read(&rr, r, d, rdtgrp, &d->hdr.cpu_mask, evtid, false);
 	}
 
 checkresult:
-
+	/*
+	 * -ENOENT is a special case, set only when "mbm_event" mode is enabled
+	 * and no counter has been assigned.
+	 */
 	if (rr.err == -EIO)
 		seq_puts(m, "Error\n");
 	else if (rr.err == -EINVAL)
 		seq_puts(m, "Unavailable\n");
+	else if (rr.err == -ENOENT)
+		seq_puts(m, "Unassigned\n");
 	else
 		seq_printf(m, "%llu\n", rr.val);
 
diff --git a/fs/resctrl/internal.h b/fs/resctrl/internal.h
index 4496c359ac22..4a7130018aa1 100644
--- a/fs/resctrl/internal.h
+++ b/fs/resctrl/internal.h
@@ -390,6 +390,8 @@ int resctrl_assign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
 			      struct rdtgroup *rdtgrp, struct mon_evt *mevt);
 void resctrl_unassign_cntr_event(struct rdt_resource *r, struct rdt_mon_domain *d,
 				 struct rdtgroup *rdtgrp, struct mon_evt *mevt);
+int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
+		 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid);
 
 #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 f2636aea6545..cf7f6a22ea51 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -977,8 +977,8 @@ static void resctrl_config_cntr(struct rdt_resource *r, struct rdt_mon_domain *d
  * Return:
  * Valid counter ID on success, or -ENOENT on failure.
  */
-static int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
-			struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
+int mbm_cntr_get(struct rdt_resource *r, struct rdt_mon_domain *d,
+		 struct rdtgroup *rdtgrp, enum resctrl_event_id evtid)
 {
 	int cntr_id;
 
-- 
2.34.1