diff --git a/hw/s390x/cpu-topology.c b/hw/s390x/cpu-topology.c
index b7131b4ac3..74e04fd68e 100644
--- a/hw/s390x/cpu-topology.c
+++ b/hw/s390x/cpu-topology.c
@@ -127,15 +127,14 @@ void s390_topology_new_cpu(int core_id)
     S390TopologyBook *book;
     S390TopologySocket *socket;
     S390TopologyCores *cores;
-    int cores_per_socket, sock_idx;
     int origin, bit;
+    int nb_cores_per_socket;
 
     book = s390_get_topology();
 
-    cores_per_socket = ms->smp.max_cpus / ms->smp.sockets;
-
-    sock_idx = (core_id / cores_per_socket);
-    socket = s390_get_socket(book, sock_idx);
+    /* Cores for the S390 topology are cores and threads of the QEMU topology */
+    nb_cores_per_socket = ms->smp.cores * ms->smp.threads;
+    socket = s390_get_socket(book, core_id / nb_cores_per_socket);
 
     /*
      * At the core level, each CPU is represented by a bit in a 64bit
@@ -151,12 +150,11 @@ void s390_topology_new_cpu(int core_id)
      * CPU inside several CPU containers inside the socket container.
      */
     origin = 64 * (core_id / 64);
-
     cores = s390_get_cores(socket, origin);
+    cores->origin = origin;
 
     bit = 63 - (core_id - origin);
     set_bit(bit, &cores->mask);
-    cores->origin = origin;
 }
 
 /*
diff --git a/target/s390x/cpu.h b/target/s390x/cpu.h
index f6969b76c5..a617c943ff 100644
--- a/target/s390x/cpu.h
+++ b/target/s390x/cpu.h
@@ -889,4 +889,5 @@ S390CPU *s390_cpu_addr2state(uint16_t cpu_addr);
 
 #include "exec/cpu-all.h"
 
+void insert_stsi_15_1_x(S390CPU *cpu, int sel2, __u64 addr, uint8_t ar);
 #endif
diff --git a/target/s390x/cpu_topology.c b/target/s390x/cpu_topology.c
new file mode 100644
index 0000000000..7f6db18829
--- /dev/null
+++ b/target/s390x/cpu_topology.c
@@ -0,0 +1,112 @@
+/*
+ * QEMU S390x CPU Topology
+ *
+ * Copyright IBM Corp. 2021
+ * Author(s): Pierre Morel <pmorel@linux.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or (at
+ * your option) any later version. See the COPYING file in the top-level
+ * directory.
+ */
+
+#include "qemu/osdep.h"
+#include "cpu.h"
+#include "hw/s390x/pv.h"
+#include "hw/sysbus.h"
+#include "hw/s390x/cpu-topology.h"
+
+static int stsi_15_container(void *p, int nl, int id)
+{
+    SysIBTl_container *tle = (SysIBTl_container *)p;
+
+    tle->nl = nl;
+    tle->id = id;
+
+    return sizeof(*tle);
+}
+
+static int stsi_15_cpus(void *p, S390TopologyCores *cd)
+{
+    SysIBTl_cpu *tle = (SysIBTl_cpu *)p;
+
+    tle->nl = 0;
+    tle->dedicated = cd->dedicated;
+    tle->polarity = cd->polarity;
+    tle->type = cd->cputype;
+    tle->origin = be16_to_cpu(cd->origin);
+    tle->mask = be64_to_cpu(cd->mask);
+
+    return sizeof(*tle);
+}
+
+static int set_socket(const MachineState *ms, void *p,
+                      S390TopologySocket *socket)
+{
+    BusChild *kid;
+    int l, len = 0;
+
+    len += stsi_15_container(p, 1, socket->socket_id);
+    p += len;
+
+    QTAILQ_FOREACH_REVERSE(kid, &socket->bus->children, sibling) {
+        l = stsi_15_cpus(p, S390_TOPOLOGY_CORES(kid->child));
+        p += l;
+        len += l;
+    }
+    return len;
+}
+
+static void setup_stsi(const MachineState *ms, void *p, int level)
+{
+    S390TopologyBook *book;
+    SysIB_151x *sysib;
+    BusChild *kid;
+    int len, l;
+
+    sysib = (SysIB_151x *)p;
+    sysib->mnest = level;
+    sysib->mag[TOPOLOGY_NR_MAG2] = ms->smp.sockets;
+    sysib->mag[TOPOLOGY_NR_MAG1] = ms->smp.cores * ms->smp.threads;
+
+    book = s390_get_topology();
+    len = sizeof(SysIB_151x);
+    p += len;
+
+    QTAILQ_FOREACH_REVERSE(kid, &book->bus->children, sibling) {
+        l = set_socket(ms, p, S390_TOPOLOGY_SOCKET(kid->child));
+        p += l;
+        len += l;
+    }
+
+    sysib->length = be16_to_cpu(len);
+}
+
+void insert_stsi_15_1_x(S390CPU *cpu, int sel2, __u64 addr, uint8_t ar)
+{
+    const MachineState *machine = MACHINE(qdev_get_machine());
+    void *p;
+    int ret, cc;
+
+    /*
+     * Until the SCLP STSI Facility reporting the MNEST value is used,
+     * a sel2 value of 2 is the only value allowed in STSI 15.1.x.
+     */
+    if (sel2 != 2) {
+        setcc(cpu, 3);
+        return;
+    }
+
+    p = g_malloc0(TARGET_PAGE_SIZE);
+
+    setup_stsi(machine, p, 2);
+
+    if (s390_is_pv()) {
+        ret = s390_cpu_pv_mem_write(cpu, 0, p, TARGET_PAGE_SIZE);
+    } else {
+        ret = s390_cpu_virt_mem_write(cpu, addr, ar, p, TARGET_PAGE_SIZE);
+    }
+    cc = ret ? 3 : 0;
+    setcc(cpu, cc);
+    g_free(p);
+}
+
diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
index 6acf14d5ec..27b3fbfa09 100644
--- a/target/s390x/kvm/kvm.c
+++ b/target/s390x/kvm/kvm.c
@@ -52,6 +52,7 @@
 #include "hw/s390x/s390-virtio-ccw.h"
 #include "hw/s390x/s390-virtio-hcall.h"
 #include "hw/s390x/pv.h"
+#include "hw/s390x/cpu-topology.h"
 
 #ifndef DEBUG_KVM
 #define DEBUG_KVM  0
@@ -1910,6 +1911,10 @@ static int handle_stsi(S390CPU *cpu)
         /* Only sysib 3.2.2 needs post-handling for now. */
         insert_stsi_3_2_2(cpu, run->s390_stsi.addr, run->s390_stsi.ar);
         return 0;
+    case 15:
+        insert_stsi_15_1_x(cpu, run->s390_stsi.sel2, run->s390_stsi.addr,
+                           run->s390_stsi.ar);
+        return 0;
     default:
         return 0;
     }
diff --git a/target/s390x/meson.build b/target/s390x/meson.build
index 84c1402a6a..890ccfa789 100644
--- a/target/s390x/meson.build
+++ b/target/s390x/meson.build
@@ -29,6 +29,7 @@ s390x_softmmu_ss.add(files(
   'sigp.c',
   'cpu-sysemu.c',
   'cpu_models_sysemu.c',
+  'cpu_topology.c',
 ))
 
 s390x_user_ss = ss.source_set()
