x86/resctrl: Add end-marker to the resctrl_event_id enum

The resctrl_event_id enum gives names to the counter event numbers on x86.
These are used directly by resctrl.

To allow the MPAM driver to keep an array of these the size of the enum
needs to be known.

Add a 'num_events' enum entry which can be used to size an array.  This is
added to the enum to reduce conflicts with another series, which in turn
requires get_arch_mbm_state() to have a default case.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Fenghua Yu <fenghuay@nvidia.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Tested-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/20250515165855.31452-12-james.morse@arm.com

arch/x86/kernel/cpu/resctrl/monitor.c

@@ -260,12 +260,11 @@ static struct arch_mbm_state *get_arch_mbm_state(struct rdt_hw_mon_domain *hw_do
 		return &hw_dom->arch_mbm_total[rmid];
 	case QOS_L3_MBM_LOCAL_EVENT_ID:
 		return &hw_dom->arch_mbm_local[rmid];
+	default:
+		/* Never expect to get here */
+		WARN_ON_ONCE(1);
+		return NULL;
 	}
-
-	/* Never expect to get here */
-	WARN_ON_ONCE(1);
-
-	return NULL;
 }
 
 void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_mon_domain *d,

include/linux/resctrl_types.h

@@ -49,6 +49,9 @@ enum resctrl_event_id {
 	QOS_L3_OCCUP_EVENT_ID		= 0x01,
 	QOS_L3_MBM_TOTAL_EVENT_ID	= 0x02,
 	QOS_L3_MBM_LOCAL_EVENT_ID	= 0x03,
+
+	/* Must be the last */
+	QOS_NUM_EVENTS,
 };
 
 #endif /* __LINUX_RESCTRL_TYPES_H */