diff --git a/hw/cpu/cluster.c b/hw/cpu/cluster.c
index 9d50a235d5ce4b410bd34a9a427ec8a683fbb9a1..25f90702b16e89caf6813497398359de873885d5 100644
--- a/hw/cpu/cluster.c
+++ b/hw/cpu/cluster.c
@@ -20,19 +20,65 @@
 
 #include "qemu/osdep.h"
 #include "hw/cpu/cluster.h"
+#include "qom/cpu.h"
 #include "qapi/error.h"
 #include "qemu/module.h"
+#include "qemu/cutils.h"
 
 static Property cpu_cluster_properties[] = {
     DEFINE_PROP_UINT32("cluster-id", CPUClusterState, cluster_id, 0),
     DEFINE_PROP_END_OF_LIST()
 };
 
+typedef struct CallbackData {
+    CPUClusterState *cluster;
+    int cpu_count;
+} CallbackData;
+
+static int add_cpu_to_cluster(Object *obj, void *opaque)
+{
+    CallbackData *cbdata = opaque;
+    CPUState *cpu = (CPUState *)object_dynamic_cast(obj, TYPE_CPU);
+
+    if (cpu) {
+        cpu->cluster_index = cbdata->cluster->cluster_id;
+        cbdata->cpu_count++;
+    }
+    return 0;
+}
+
+static void cpu_cluster_realize(DeviceState *dev, Error **errp)
+{
+    /* Iterate through all our CPU children and set their cluster_index */
+    CPUClusterState *cluster = CPU_CLUSTER(dev);
+    Object *cluster_obj = OBJECT(dev);
+    CallbackData cbdata = {
+        .cluster = cluster,
+        .cpu_count = 0,
+    };
+
+    if (cluster->cluster_id >= MAX_CLUSTERS) {
+        error_setg(errp, "cluster-id must be less than %d", MAX_CLUSTERS);
+        return;
+    }
+
+    object_child_foreach_recursive(cluster_obj, add_cpu_to_cluster, &cbdata);
+
+    /*
+     * A cluster with no CPUs is a bug in the board/SoC code that created it;
+     * if you hit this during development of new code, check that you have
+     * created the CPUs and parented them into the cluster object before
+     * realizing the cluster object.
+     */
+    assert(cbdata.cpu_count > 0);
+}
+
 static void cpu_cluster_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
 
     dc->props = cpu_cluster_properties;
+    dc->realize = cpu_cluster_realize;
 }
 
 static const TypeInfo cpu_cluster_type_info = {
diff --git a/include/hw/cpu/cluster.h b/include/hw/cpu/cluster.h
index 73818232437f5cfa99de8cdcb7fc4eeb028af658..549c2d31d438a8ea3c7ca0f2baa794988bbc6464 100644
--- a/include/hw/cpu/cluster.h
+++ b/include/hw/cpu/cluster.h
@@ -34,12 +34,36 @@
  * Arm big.LITTLE system) they should be in different clusters. If the CPUs do
  * not have the same view of memory (for example the main CPU and a management
  * controller processor) they should be in different clusters.
+ *
+ * A cluster is created by creating an object of TYPE_CPU_CLUSTER, and then
+ * adding the CPUs to it as QOM child objects (e.g. using the
+ * object_initialize_child() or object_property_add_child() functions).
+ * The CPUs may be either direct children of the cluster object, or indirect
+ * children (e.g. children of children of the cluster object).
+ *
+ * All CPUs must be added as children before the cluster is realized.
+ * (Regrettably QOM provides no way to prevent adding children to a realized
+ * object and no way for the parent to be notified when a new child is added
+ * to it, so this restriction is not checked for, but the system will not
+ * behave correctly if it is not adhered to. The cluster will assert that
+ * it contains at least one CPU, which should catch most inadvertent
+ * violations of this constraint.)
+ *
+ * A CPU which is not put into any cluster will be considered implicitly
+ * to be in a cluster with all the other "loose" CPUs, so all CPUs that are
+ * not assigned to clusters must be identical.
  */
 
 #define TYPE_CPU_CLUSTER "cpu-cluster"
 #define CPU_CLUSTER(obj) \
     OBJECT_CHECK(CPUClusterState, (obj), TYPE_CPU_CLUSTER)
 
+/*
+ * This limit is imposed by TCG, which puts the cluster ID into an
+ * 8 bit field (and uses all-1s for the default "not in any cluster").
+ */
+#define MAX_CLUSTERS 255
+
 /**
  * CPUClusterState:
  * @cluster_id: The cluster ID. This value is for internal use only and should
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 16bbed1ae0926e368af89c5f0628be7e486c4e42..4c2feb9c17bfd39e64867049cacc09c1bd2c8a48 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -280,6 +280,11 @@ struct qemu_work_item;
 /**
  * CPUState:
  * @cpu_index: CPU index (informative).
+ * @cluster_index: Identifies which cluster this CPU is in.
+ *   For boards which don't define clusters or for "loose" CPUs not assigned
+ *   to a cluster this will be UNASSIGNED_CLUSTER_INDEX; otherwise it will
+ *   be the same as the cluster-id property of the CPU object's TYPE_CPU_CLUSTER
+ *   QOM parent.
  * @nr_cores: Number of cores within this CPU package.
  * @nr_threads: Number of threads within this CPU.
  * @running: #true if CPU is currently running (lockless).
@@ -405,6 +410,7 @@ struct CPUState {
 
     /* TODO Move common fields from CPUArchState here. */
     int cpu_index;
+    int cluster_index;
     uint32_t halted;
     uint32_t can_do_io;
     int32_t exception_index;
@@ -1111,5 +1117,6 @@ extern const struct VMStateDescription vmstate_cpu_common;
 #endif /* NEED_CPU_H */
 
 #define UNASSIGNED_CPU_INDEX -1
+#define UNASSIGNED_CLUSTER_INDEX -1
 
 #endif
diff --git a/qom/cpu.c b/qom/cpu.c
index 5442a7323be5efb1d925d13953f3f9ed48cef703..f5579b1cd50abd30687a52ed501640c478f59806 100644
--- a/qom/cpu.c
+++ b/qom/cpu.c
@@ -364,6 +364,7 @@ static void cpu_common_initfn(Object *obj)
     CPUClass *cc = CPU_GET_CLASS(obj);
 
     cpu->cpu_index = UNASSIGNED_CPU_INDEX;
+    cpu->cluster_index = UNASSIGNED_CLUSTER_INDEX;
     cpu->gdb_num_regs = cpu->gdb_num_g_regs = cc->gdb_num_core_regs;
     /* *-user doesn't have configurable SMP topology */
     /* the default value is changed by qemu_init_vcpu() for softmmu */