[PATCH v8 20/25] x86/resctrl: Report "Unassigned" for MBM events in mbm_cntr_assign mode

[Babu Moger]

In mbm_cntr_assign mode, the hardware counter should be assigned to read
the MBM events.

Report "Unassigned" in case the user attempts to read the events without
assigning the counter.

Signed-off-by: Babu Moger <babu.moger@xxxxxxx>
---
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/arch/x86/resctrl.rst        | 10 ++++++++++
 arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 13 ++++++++++++-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/Documentation/arch/x86/resctrl.rst b/Documentation/arch/x86/resctrl.rst
index 1b5c05a35793..99ee9c87952b 100644
--- a/Documentation/arch/x86/resctrl.rst
+++ b/Documentation/arch/x86/resctrl.rst
@@ -419,6 +419,16 @@ 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.
 
+	When supported the 'mbm_cntr_assign' mode allows users to assign a
+	counter to mon_hw_id, event pair 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 counters are not reset during this period. With
+	a limited number of counters, the system may run out of assignable
+	counters at some point. In that case, MBM event counters will return
+	"Unassigned" when the event is read. Users must manually assign a
+	counter to read the events.
+
 "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/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
index 50fa1fe9a073..5a9d15b2c319 100644
--- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
+++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c
@@ -562,7 +562,7 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 	struct rdtgroup *rdtgrp;
 	struct rdt_resource *r;
 	union mon_data_bits md;
-	int ret = 0;
+	int ret = 0, index;
 
 	rdtgrp = rdtgroup_kn_lock_live(of->kn);
 	if (!rdtgrp) {
@@ -576,6 +576,15 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 	evtid = md.u.evtid;
 	r = &rdt_resources_all[resid].r_resctrl;
 
+	if (resctrl_arch_mbm_cntr_assign_enabled(r) && evtid != QOS_L3_OCCUP_EVENT_ID) {
+		index = MBM_EVENT_ARRAY_INDEX(evtid);
+		if (index != INVALID_CONFIG_INDEX &&
+		    rdtgrp->mon.cntr_id[index] == MON_CNTR_UNSET) {
+			rr.err = -ENOENT;
+			goto checkresult;
+		}
+	}
+
 	if (md.u.sum) {
 		/*
 		 * This file requires summing across all domains that share
@@ -613,6 +622,8 @@ int rdtgroup_mondata_show(struct seq_file *m, void *arg)
 		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);
 
-- 
2.34.1