diff --git a/arch/x86/include/asm/resctrl.h b/arch/x86/include/asm/resctrl.h
index d24b04ebf950..523eabfa3193 100644
--- a/arch/x86/include/asm/resctrl.h
+++ b/arch/x86/include/asm/resctrl.h
@@ -96,6 +96,23 @@ static inline void resctrl_sched_in(void)
 		__resctrl_sched_in();
 }
 
+static inline u32 resctrl_arch_system_num_rmid_idx(void)
+{
+	/* RMID are independent numbers for x86. num_rmid_idx==num_rmid */
+	return boot_cpu_data.x86_cache_max_rmid + 1;
+}
+
+static inline void resctrl_arch_rmid_idx_decode(u32 idx, u32 *closid, u32 *rmid)
+{
+	*rmid = idx;
+	*closid = ~0;
+}
+
+static inline u32 resctrl_arch_rmid_idx_encode(u32 closid, u32 rmid)
+{
+	return rmid;
+}
+
 void resctrl_cpu_detect(struct cpuinfo_x86 *c);
 
 #else
diff --git a/arch/x86/kernel/cpu/resctrl/internal.h b/arch/x86/kernel/cpu/resctrl/internal.h
index 4b243ba88882..cb94c3e3fe36 100644
--- a/arch/x86/kernel/cpu/resctrl/internal.h
+++ b/arch/x86/kernel/cpu/resctrl/internal.h
@@ -8,6 +8,8 @@
 #include <linux/fs_context.h>
 #include <linux/jump_label.h>
 
+#include <asm/resctrl.h>
+
 #define MSR_IA32_L3_QOS_CFG		0xc81
 #define MSR_IA32_L2_QOS_CFG		0xc82
 #define MSR_IA32_L3_CBM_BASE		0xc90
diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c
index f1f66c9942a5..c95d259476d4 100644
--- a/arch/x86/kernel/cpu/resctrl/monitor.c
+++ b/arch/x86/kernel/cpu/resctrl/monitor.c
@@ -137,11 +137,24 @@ static inline u64 get_corrected_mbm_count(u32 rmid, unsigned long val)
 	return val;
 }
 
-static inline struct rmid_entry *__rmid_entry(u32 closid, u32 rmid)
+/*
+ * x86 and arm64 differ in their handling of monitoring.
+ * x86's RMID are an independent number, there is one RMID '1'.
+ * arm64's PMG extend the PARTID/CLOSID space, there is one RMID '1' for each
+ * CLOSID. The RMID is no longer unique.
+ * To account for this, resctrl uses an index. On x86 this is just the RMID,
+ * on arm64 it encodes the CLOSID and RMID. This gives a unique number.
+ *
+ * The domain's rmid_busy_llc and rmid_ptrs are sized by index. The arch code
+ * must accept an attempt to read every index.
+ */
+static inline struct rmid_entry *__rmid_entry(u32 idx)
 {
 	struct rmid_entry *entry;
+	u32 closid, rmid;
 
-	entry = &rmid_ptrs[rmid];
+	entry = &rmid_ptrs[idx];
+	resctrl_arch_rmid_idx_decode(idx, &closid, &rmid);
 	WARN_ON(entry->rmid != rmid);
 
 	return entry;
@@ -238,8 +251,9 @@ int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d,
 void __check_limbo(struct rdt_domain *d, bool force_free)
 {
 	struct rdt_resource *r = &rdt_resources_all[RDT_RESOURCE_L3].r_resctrl;
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	struct rmid_entry *entry;
-	u32 crmid = 1, nrmid;
+	u32 idx, cur_idx = 1;
 	bool rmid_dirty;
 	u64 val = 0;
 
@@ -250,12 +264,11 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 	 * RMID and move it to the free list when the counter reaches 0.
 	 */
 	for (;;) {
-		nrmid = find_next_bit(d->rmid_busy_llc, r->num_rmid, crmid);
-		if (nrmid >= r->num_rmid)
+		idx = find_next_bit(d->rmid_busy_llc, idx_limit, cur_idx);
+		if (idx >= idx_limit)
 			break;
 
-		entry = __rmid_entry(~0, nrmid);	// temporary
-
+		entry = __rmid_entry(idx);
 		if (resctrl_arch_rmid_read(r, d, entry->closid, entry->rmid,
 					   QOS_L3_OCCUP_EVENT_ID, &val)) {
 			rmid_dirty = true;
@@ -264,19 +277,21 @@ void __check_limbo(struct rdt_domain *d, bool force_free)
 		}
 
 		if (force_free || !rmid_dirty) {
-			clear_bit(entry->rmid, d->rmid_busy_llc);
+			clear_bit(idx, d->rmid_busy_llc);
 			if (!--entry->busy) {
 				rmid_limbo_count--;
 				list_add_tail(&entry->list, &rmid_free_lru);
 			}
 		}
-		crmid = nrmid + 1;
+		cur_idx = idx + 1;
 	}
 }
 
 bool has_busy_rmid(struct rdt_resource *r, struct rdt_domain *d)
 {
-	return find_first_bit(d->rmid_busy_llc, r->num_rmid) != r->num_rmid;
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
+
+	return find_first_bit(d->rmid_busy_llc, idx_limit) != idx_limit;
 }
 
 /*
@@ -306,6 +321,9 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 	struct rdt_domain *d;
 	int cpu, err;
 	u64 val = 0;
+	u32 idx;
+
+	idx = resctrl_arch_rmid_idx_encode(entry->closid, entry->rmid);
 
 	entry->busy = 0;
 	cpu = get_cpu();
@@ -325,7 +343,7 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 		 */
 		if (!has_busy_rmid(r, d))
 			cqm_setup_limbo_handler(d, CQM_LIMBOCHECK_INTERVAL);
-		set_bit(entry->rmid, d->rmid_busy_llc);
+		set_bit(idx, d->rmid_busy_llc);
 		entry->busy++;
 	}
 	put_cpu();
@@ -338,14 +356,16 @@ static void add_rmid_to_limbo(struct rmid_entry *entry)
 
 void free_rmid(u32 closid, u32 rmid)
 {
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
 	struct rmid_entry *entry;
 
-	if (!rmid)
-		return;
-
 	lockdep_assert_held(&rdtgroup_mutex);
 
-	entry = __rmid_entry(closid, rmid);
+	/* do not allow the default rmid to be free'd */
+	if (!idx)
+		return;
+
+	entry = __rmid_entry(idx);
 
 	if (is_llc_occupancy_enabled())
 		add_rmid_to_limbo(entry);
@@ -355,6 +375,7 @@ void free_rmid(u32 closid, u32 rmid)
 
 static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
 {
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
 	struct mbm_state *m;
 	u64 tval = 0;
 
@@ -371,10 +392,10 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
 		rr->val += tval;
 		return 0;
 	case QOS_L3_MBM_TOTAL_EVENT_ID:
-		m = &rr->d->mbm_total[rmid];
+		m = &rr->d->mbm_total[idx];
 		break;
 	case QOS_L3_MBM_LOCAL_EVENT_ID:
-		m = &rr->d->mbm_local[rmid];
+		m = &rr->d->mbm_local[idx];
 		break;
 	default:
 		/*
@@ -407,7 +428,8 @@ static int __mon_event_count(u32 closid, u32 rmid, struct rmid_read *rr)
  */
 static void mbm_bw_count(u32 closid, u32 rmid, struct rmid_read *rr)
 {
-	struct mbm_state *m = &rr->d->mbm_local[rmid];
+	u32 idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+	struct mbm_state *m = &rr->d->mbm_local[idx];
 	u64 cur_bw, bytes, cur_bytes;
 
 	cur_bytes = rr->val;
@@ -497,7 +519,7 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 {
 	u32 closid, rmid, cur_msr_val, new_msr_val;
 	struct mbm_state *pmbm_data, *cmbm_data;
-	u32 cur_bw, delta_bw, user_bw;
+	u32 cur_bw, delta_bw, user_bw, idx;
 	struct rdt_resource *r_mba;
 	struct rdt_domain *dom_mba;
 	struct list_head *head;
@@ -510,7 +532,8 @@ static void update_mba_bw(struct rdtgroup *rgrp, struct rdt_domain *dom_mbm)
 
 	closid = rgrp->closid;
 	rmid = rgrp->mon.rmid;
-	pmbm_data = &dom_mbm->mbm_local[rmid];
+	idx = resctrl_arch_rmid_idx_encode(closid, rmid);
+	pmbm_data = &dom_mbm->mbm_local[idx];
 
 	dom_mba = get_domain_from_cpu(smp_processor_id(), r_mba);
 	if (!dom_mba) {
@@ -693,19 +716,19 @@ void mbm_setup_overflow_handler(struct rdt_domain *dom, unsigned long delay_ms)
 
 static int dom_data_init(struct rdt_resource *r)
 {
+	u32 nr_idx = resctrl_arch_system_num_rmid_idx();
 	struct rmid_entry *entry = NULL;
-	int i, nr_rmids;
+	int i;
 
-	nr_rmids = r->num_rmid;
-	rmid_ptrs = kcalloc(nr_rmids, sizeof(struct rmid_entry), GFP_KERNEL);
+	rmid_ptrs = kcalloc(nr_idx, sizeof(struct rmid_entry), GFP_KERNEL);
 	if (!rmid_ptrs)
 		return -ENOMEM;
 
-	for (i = 0; i < nr_rmids; i++) {
+	for (i = 0; i < nr_idx; i++) {
 		entry = &rmid_ptrs[i];
 		INIT_LIST_HEAD(&entry->list);
 
-		entry->rmid = i;
+		resctrl_arch_rmid_idx_decode(i, &entry->closid, &entry->rmid);
 		list_add_tail(&entry->list, &rmid_free_lru);
 	}
 
@@ -714,7 +737,7 @@ static int dom_data_init(struct rdt_resource *r)
 	 * default_rdtgroup control group, which will be setup later. See
 	 * rdtgroup_setup_root().
 	 */
-	entry = __rmid_entry(0, 0);
+	entry = __rmid_entry(resctrl_arch_rmid_idx_encode(0, 0));
 	list_del(&entry->list);
 
 	return 0;
diff --git a/arch/x86/kernel/cpu/resctrl/rdtgroup.c b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
index f3b739c52e42..9ce4746778f4 100644
--- a/arch/x86/kernel/cpu/resctrl/rdtgroup.c
+++ b/arch/x86/kernel/cpu/resctrl/rdtgroup.c
@@ -3320,16 +3320,17 @@ void resctrl_offline_domain(struct rdt_resource *r, struct rdt_domain *d)
 
 static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 {
+	u32 idx_limit = resctrl_arch_system_num_rmid_idx();
 	size_t tsize;
 
 	if (is_llc_occupancy_enabled()) {
-		d->rmid_busy_llc = bitmap_zalloc(r->num_rmid, GFP_KERNEL);
+		d->rmid_busy_llc = bitmap_zalloc(idx_limit, GFP_KERNEL);
 		if (!d->rmid_busy_llc)
 			return -ENOMEM;
 	}
 	if (is_mbm_total_enabled()) {
 		tsize = sizeof(*d->mbm_total);
-		d->mbm_total = kcalloc(r->num_rmid, tsize, GFP_KERNEL);
+		d->mbm_total = kcalloc(idx_limit, tsize, GFP_KERNEL);
 		if (!d->mbm_total) {
 			bitmap_free(d->rmid_busy_llc);
 			return -ENOMEM;
@@ -3337,7 +3338,7 @@ static int domain_setup_mon_state(struct rdt_resource *r, struct rdt_domain *d)
 	}
 	if (is_mbm_local_enabled()) {
 		tsize = sizeof(*d->mbm_local);
-		d->mbm_local = kcalloc(r->num_rmid, tsize, GFP_KERNEL);
+		d->mbm_local = kcalloc(idx_limit, tsize, GFP_KERNEL);
 		if (!d->mbm_local) {
 			bitmap_free(d->rmid_busy_llc);
 			kfree(d->mbm_total);
