[PATCH v12 11/25] fs/resctrl: Add interface to disable a monitor event

[Tony Luck <tony.luck@intel.com>]

resctrl currently assumes all monitor events are enabled before any domain
is created, because per-domain state is allocated by the architecture's CPU
hotplug callbacks. There is no way to disable an event once registered.

AET events are enumerated by the INTEL_PMT_TELEMETRY driver. To allow that
driver to be a loadable module, resctrl must tolerate AET events appearing
and disappearing, which requires the ability to disable an event when the
driver is unloaded.

Add resctrl_disable_mon_event(). The architecture owns domain lifetime
and knows mount state, so it is responsible for calling this only while
resctrl is unmounted and for cleaning up any per-domain state. Document
those requirements in the kerneldoc since they are not enforced in code.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
---
v12:
	Added Reinette RB tag (from v10 review).
	Better header comment for resctrl_disable_mon_event().
---
 include/linux/resctrl.h | 34 ++++++++++++++++++++++++++++++++++
 fs/resctrl/monitor.c    | 15 +++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/include/linux/resctrl.h b/include/linux/resctrl.h
index 6b07ac2c8675..fbf737e884db 100644
--- a/include/linux/resctrl.h
+++ b/include/linux/resctrl.h
@@ -449,9 +449,43 @@ u32 resctrl_arch_get_num_closid(struct rdt_resource *r);
 u32 resctrl_arch_system_num_rmid_idx(void);
 int resctrl_arch_update_domains(struct rdt_resource *r, u32 closid);
 
+/**
+ * resctrl_enable_mon_event() - Enable monitoring event
+ * @eventid:	ID of the event
+ * @any_cpu:	True if event data can be read from any CPU.
+ * @binary_bits: Number of binary places of the fixed-point value expected to
+ *		back a floating point event. Can only be set for floating point
+ *		events.
+ * @arch_priv:  Architecture private data associated with event. Passed back to
+ *		architecture when reading the event via resctrl_arch_rmid_read().
+ *
+ * The file system must not be mounted when enabling an event.
+ *
+ * Events that require per-domain (architectural and/or filesystem) state must
+ * be enabled before the domain structures are allocated. For example before
+ * CPU hotplug callbacks that allocate domain structures are registered. If the
+ * architecture discovers a resource after initialization it should enable
+ * events needing per-domain state before any domain structure allocation which
+ * should be coordinated with the CPU hotplug callbacks.
+ *
+ * Return:
+ * true if event was successfully enabled, false otherwise.
+ */
 bool resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu,
 			      unsigned int binary_bits, void *arch_priv);
 
+/**
+ * resctrl_disable_mon_event() - Disable monitoring event
+ * @eventid:	ID of the event
+ *
+ * Never disable an event that may be accessed while the file system is unmounted.
+ *
+ * Events that require per-domain (architectural and/or filesystem) state
+ * will require additional cleanup which should be coordinated with the CPU
+ * hotplug callbacks.
+ */
+void resctrl_disable_mon_event(enum resctrl_event_id eventid);
+
 bool resctrl_is_mon_event_enabled(enum resctrl_event_id eventid);
 
 bool resctrl_arch_is_evt_configurable(enum resctrl_event_id evt);
diff --git a/fs/resctrl/monitor.c b/fs/resctrl/monitor.c
index 02e81fc82b14..2a28fe04284b 100644
--- a/fs/resctrl/monitor.c
+++ b/fs/resctrl/monitor.c
@@ -1066,6 +1066,21 @@ bool resctrl_enable_mon_event(enum resctrl_event_id eventid, bool any_cpu,
 	return true;
 }
 
+void resctrl_disable_mon_event(enum resctrl_event_id eventid)
+{
+	if (WARN_ON_ONCE(eventid < QOS_FIRST_EVENT || eventid >= QOS_NUM_EVENTS))
+		return;
+	if (!mon_event_all[eventid].enabled) {
+		pr_warn("Event %d already disabled\n", eventid);
+		return;
+	}
+
+	mon_event_all[eventid].any_cpu = false;
+	mon_event_all[eventid].binary_bits = 0;
+	mon_event_all[eventid].arch_priv = NULL;
+	mon_event_all[eventid].enabled = false;
+}
+
 bool resctrl_is_mon_event_enabled(enum resctrl_event_id eventid)
 {
 	return eventid >= QOS_FIRST_EVENT && eventid < QOS_NUM_EVENTS &&
-- 
2.55.0