s390x/cpu topology: resetting the Topology-Change-Report

During a subsystem reset the Topology-Change-Report is cleared
by the machine.
Let's ask KVM to clear the Modified Topology Change Report (MTCR)
bit of the SCA in the case of a subsystem reset.

Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Co-developed-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Signed-off-by: Nina Schoetterl-Glausch <nsg@linux.ibm.com>
Message-ID: <20231016183925.2384704-7-nsg@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

hw/s390x/cpu-topology.c

@@ -90,6 +90,17 @@ static void s390_topology_init(MachineState *ms)
                                             smp->books * smp->drawers);
 }
 
+/**
+ * s390_topology_reset:
+ *
+ * Generic reset for CPU topology, calls s390_topology_reset()
+ * to reset the kernel Modified Topology Change Record.
+ */
+void s390_topology_reset(void)
+{
+    s390_cpu_topology_set_changed(false);
+}
+
 /**
  * s390_topology_cpu_default:
  * @cpu: pointer to a S390CPU

hw/s390x/s390-virtio-ccw.c

@@ -124,6 +124,9 @@ static void subsystem_reset(void)
             device_cold_reset(dev);
         }
     }
+    if (s390_has_topology()) {
+        s390_topology_reset();
+    }
 }
 
 static int virtio_ccw_hcall_notify(const uint64_t *args)

include/hw/s390x/cpu-topology.h

@@ -45,6 +45,7 @@ typedef QTAILQ_HEAD(, S390TopologyEntry) S390TopologyList;
 #ifdef CONFIG_KVM
 bool s390_has_topology(void);
 void s390_topology_setup_cpu(MachineState *ms, S390CPU *cpu, Error **errp);
+void s390_topology_reset(void);
 #else
 static inline bool s390_has_topology(void)
 {
@@ -53,6 +54,11 @@ static inline bool s390_has_topology(void)
 static inline void s390_topology_setup_cpu(MachineState *ms,
                                            S390CPU *cpu,
                                            Error **errp) {}
+static inline void s390_topology_reset(void)
+{
+    /* Unreachable, CPU topology not implemented for TCG */
+    assert(false);
+}
 #endif
 
 extern S390Topology s390_topology;

target/s390x/cpu-sysemu.c

@@ -307,3 +307,16 @@ void s390_do_cpu_set_diag318(CPUState *cs, run_on_cpu_data arg)
         kvm_s390_set_diag318(cs, arg.host_ulong);
     }
 }
+
+void s390_cpu_topology_set_changed(bool changed)
+{
+    int ret;
+
+    if (kvm_enabled()) {
+        ret = kvm_s390_topology_set_mtcr(changed);
+        if (ret) {
+            error_report("Failed to set Modified Topology Change Report: %s",
+                         strerror(-ret));
+        }
+    }
+}

target/s390x/cpu.h

@@ -654,6 +654,7 @@ typedef struct SysIBCPUListEntry {
 QEMU_BUILD_BUG_ON(sizeof(SysIBCPUListEntry) != 16);
 
 void insert_stsi_15_1_x(S390CPU *cpu, int sel2, uint64_t addr, uint8_t ar, uintptr_t ra);
+void s390_cpu_topology_set_changed(bool changed);
 
 /* MMU defines */
 #define ASCE_ORIGIN           (~0xfffULL) /* segment table origin             */

target/s390x/kvm/kvm.c

@@ -2664,6 +2664,23 @@ int kvm_s390_get_zpci_op(void)
     return cap_zpci_op;
 }
 
+int kvm_s390_topology_set_mtcr(uint64_t attr)
+{
+    struct kvm_device_attr attribute = {
+        .group = KVM_S390_VM_CPU_TOPOLOGY,
+        .attr  = attr,
+    };
+
+    if (!s390_has_feat(S390_FEAT_CONFIGURATION_TOPOLOGY)) {
+        return 0;
+    }
+    if (!kvm_vm_check_attr(kvm_state, KVM_S390_VM_CPU_TOPOLOGY, attr)) {
+        return -ENOTSUP;
+    }
+
+    return kvm_vm_ioctl(kvm_state, KVM_SET_DEVICE_ATTR, &attribute);
+}
+
 void kvm_arch_accel_class_init(ObjectClass *oc)
 {
 }

target/s390x/kvm/kvm_s390x.h

@@ -47,5 +47,6 @@ void kvm_s390_crypto_reset(void);
 void kvm_s390_restart_interrupt(S390CPU *cpu);
 void kvm_s390_stop_interrupt(S390CPU *cpu);
 void kvm_s390_set_diag318(CPUState *cs, uint64_t diag318_info);
+int kvm_s390_topology_set_mtcr(uint64_t attr);
 
 #endif /* KVM_S390X_H */