[Qemu-ppc] [RFC PATCH v3 20/24] spapr: CPU hot unplug support

[Bharata B Rao]

Support hot removal of CPU for sPAPR guests by sending the hot unplug
notification to the guest via EPOW interrupt. Release the vCPU object
after CPU hot unplug so that vCPU fd can be parked and reused.

Signed-off-by: Bharata B Rao <address@hidden>
---
 hw/ppc/spapr.c              | 101 +++++++++++++++++++++++++++++++++++++++++++-
 target-ppc/translate_init.c |  10 +++++
 2 files changed, 110 insertions(+), 1 deletion(-)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 9b0701c..910a50f 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -1481,6 +1481,12 @@ static void spapr_cpu_init(PowerPCCPU *cpu)
     qemu_register_reset(spapr_cpu_reset, cpu);
 }
 
+static void spapr_cpu_destroy(PowerPCCPU *cpu)
+{
+    xics_cpu_destroy(spapr->icp, cpu);
+    qemu_unregister_reset(spapr_cpu_reset, cpu);
+}
+
 /* pSeries LPAR / sPAPR hardware init */
 static void ppc_spapr_init(MachineState *machine)
 {
@@ -1883,6 +1889,24 @@ static void *spapr_populate_hotplug_cpu_dt(DeviceState 
*dev, CPUState *cs,
     return fdt;
 }
 
+static void spapr_cpu_release(DeviceState *dev, void *opaque)
+{
+    CPUState *cs;
+    int i;
+    int id = ppc_get_vcpu_dt_id(POWERPC_CPU(CPU(dev)));
+
+    for (i = id; i < id + smp_threads; i++) {
+        CPU_FOREACH(cs) {
+            PowerPCCPU *cpu = POWERPC_CPU(cs);
+
+            if (i == ppc_get_vcpu_dt_id(cpu)) {
+                spapr_cpu_destroy(cpu);
+                cpu_remove(cs);
+            }
+        }
+    }
+}
+
 static void spapr_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                             Error **errp)
 {
@@ -1970,6 +1994,59 @@ static void spapr_cpu_plug(HotplugHandler *hotplug_dev, 
DeviceState *dev,
     return;
 }
 
+static int spapr_cpu_unplug(Object *obj, void *opaque)
+{
+    Error **errp = opaque;
+    DeviceState *dev = DEVICE(obj);
+    CPUState *cs = CPU(dev);
+    PowerPCCPU *cpu = POWERPC_CPU(cs);
+    int id = ppc_get_vcpu_dt_id(cpu);
+    int smt = kvmppc_smt_threads();
+    sPAPRDRConnector *drc =
+        spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
+    sPAPRDRConnectorClass *drck;
+    Error *local_err = NULL;
+
+    /*
+     * SMT threads return from here, only main thread (core) will
+     * continue and signal hot unplug event to the guest.
+     */
+    if ((id % smt) != 0) {
+        return 0;
+    }
+    g_assert(drc);
+
+    drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
+    drck->detach(drc, dev, spapr_cpu_release, NULL, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return -1;
+    }
+
+    /*
+     * In addition to hotplugged CPUs, send the hot-unplug notification
+     * interrupt to the guest for coldplugged CPUs started via -device
+     * option too.
+     */
+    spapr_hotplug_req_remove_event(drc);
+
+    return 0;
+}
+
+static int spapr_cpu_core_unplug(Object *obj, void *opaque)
+{
+    Error **errp = opaque;
+
+    object_child_foreach(obj, spapr_cpu_unplug, errp);
+    return 0;
+}
+
+static void spapr_cpu_socket_unplug(HotplugHandler *hotplug_dev,
+                            DeviceState *dev, Error **errp)
+{
+    object_child_foreach(OBJECT(dev), spapr_cpu_core_unplug, errp);
+}
+
 static void spapr_machine_device_plug(HotplugHandler *hotplug_dev,
                                       DeviceState *dev, Error **errp)
 {
@@ -1984,16 +2061,36 @@ static void spapr_machine_device_plug(HotplugHandler 
*hotplug_dev,
          * Fail hotplug on machines where CPU DR isn't enabled.
          */
         if (!spapr->dr_cpu_enabled && dev->hotplugged) {
+            /*
+             * FIXME: Ideally should fail hotplug here by doing an error_setg,
+             * but failing hotplug here doesn't work well with the vCPU object
+             * removal code. Hence silently refusing to add CPUs here.
+             */
+            spapr_cpu_destroy(cpu);
+            cpu_remove(cs);
             return;
         }
         spapr_cpu_plug(hotplug_dev, dev, errp);
     }
 }
 
+static void spapr_machine_device_unplug(HotplugHandler *hotplug_dev,
+                                      DeviceState *dev, Error **errp)
+{
+    if (object_dynamic_cast(OBJECT(dev), TYPE_CPU_SOCKET)) {
+        if (!spapr->dr_cpu_enabled) {
+            error_setg(errp, "CPU hot unplug not supported on this machine");
+            return;
+        }
+        spapr_cpu_socket_unplug(hotplug_dev, dev, errp);
+    }
+}
+
 static HotplugHandler *spapr_get_hotpug_handler(MachineState *machine,
                                              DeviceState *dev)
 {
-    if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
+    if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) ||
+        object_dynamic_cast(OBJECT(dev), TYPE_CPU_SOCKET)) {
         return HOTPLUG_HANDLER(machine);
     }
     return NULL;
@@ -2017,6 +2114,8 @@ static void spapr_machine_class_init(ObjectClass *oc, 
void *data)
     mc->has_dynamic_sysbus = true;
     mc->get_hotplug_handler = spapr_get_hotpug_handler;
     hc->plug = spapr_machine_device_plug;
+    hc->unplug = spapr_machine_device_unplug;
+
     smc->dr_phb_enabled = false;
     smc->dr_cpu_enabled = false;
     smc->dr_lmb_enabled = false;
diff --git a/target-ppc/translate_init.c b/target-ppc/translate_init.c
index fccee82..8e24235 100644
--- a/target-ppc/translate_init.c
+++ b/target-ppc/translate_init.c
@@ -30,6 +30,7 @@
 #include "qemu/error-report.h"
 #include "qapi/visitor.h"
 #include "hw/qdev-properties.h"
+#include "migration/vmstate.h"
 
 //#define PPC_DUMP_CPU
 //#define PPC_DEBUG_SPR
@@ -9143,9 +9144,18 @@ static void ppc_cpu_unrealizefn(DeviceState *dev, Error 
**errp)
 {
     PowerPCCPU *cpu = POWERPC_CPU(dev);
     CPUPPCState *env = &cpu->env;
+    CPUClass *cc = CPU_GET_CLASS(dev);
     opc_handler_t **table;
     int i, j;
 
+    if (qdev_get_vmsd(dev) == NULL) {
+        vmstate_unregister(NULL, &vmstate_cpu_common, cpu);
+    }
+
+    if (cc->vmsd != NULL) {
+        vmstate_unregister(NULL, cc->vmsd, cpu);
+    }
+
     cpu_exec_exit(CPU(dev));
 
     for (i = 0; i < PPC_CPU_OPCODES_LEN; i++) {
-- 
2.1.0