[Qemu-devel] [RFC PATCH v1 10/10] spapr: CPU hot unplug support

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

Remove the CPU core device by removing the underlying CPU thread devices.
Hot removal of CPU for sPAPR guests is supported 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 <bharata@linux.vnet.ibm.com>
---
 hw/ppc/spapr.c                  | 16 ++++++++
 hw/ppc/spapr_cpu_core.c         | 84 +++++++++++++++++++++++++++++++++++++++++
 include/hw/ppc/spapr.h          |  1 +
 include/hw/ppc/spapr_cpu_core.h | 11 ++++++
 4 files changed, 112 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index 6c4ac50..a42f8c0 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -2379,11 +2379,27 @@ static void spapr_machine_device_plug(HotplugHandler *hotplug_dev,
     }
 }
 
+void spapr_cpu_destroy(PowerPCCPU *cpu)
+{
+    sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
+
+    xics_cpu_destroy(spapr->icp, cpu);
+    qemu_unregister_reset(spapr_cpu_reset, cpu);
+}
+
 static void spapr_machine_device_unplug(HotplugHandler *hotplug_dev,
                                       DeviceState *dev, Error **errp)
 {
+    sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(qdev_get_machine());
+
     if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
         error_setg(errp, "Memory hot unplug not supported by sPAPR");
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_SPAPR_CPU_CORE)) {
+        if (!smc->dr_cpu_enabled) {
+            error_setg(errp, "CPU hot unplug not supported on this machine");
+            return;
+        }
+        spapr_core_unplug(hotplug_dev, dev, errp);
     }
 }
 
diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
index 4c233d7..5156eb3 100644
--- a/hw/ppc/spapr_cpu_core.c
+++ b/hw/ppc/spapr_cpu_core.c
@@ -73,6 +73,90 @@ void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
     }
 }
 
+static void spapr_cpu_core_cleanup(struct sPAPRCPUUnplugList *unplug_list)
+{
+    sPAPRCPUUnplug *unplug, *next;
+    Object *cpu;
+
+    QLIST_FOREACH_SAFE(unplug, unplug_list, node, next) {
+        cpu = unplug->cpu;
+        object_unparent(cpu);
+        QLIST_REMOVE(unplug, node);
+        g_free(unplug);
+    }
+}
+
+static void spapr_add_cpu_to_unplug_list(Object *cpu,
+                                         struct sPAPRCPUUnplugList *unplug_list)
+{
+    sPAPRCPUUnplug *unplug = g_malloc(sizeof(*unplug));
+
+    unplug->cpu = cpu;
+    QLIST_INSERT_HEAD(unplug_list, unplug, node);
+}
+
+static int spapr_cpu_release(Object *obj, void *opaque)
+{
+    DeviceState *dev = DEVICE(obj);
+    CPUState *cs = CPU(dev);
+    PowerPCCPU *cpu = POWERPC_CPU(cs);
+    struct sPAPRCPUUnplugList *unplug_list = opaque;
+
+    spapr_cpu_destroy(cpu);
+    cpu_remove_sync(cs);
+
+    /*
+     * We are still walking the core object's children list, and
+     * hence can't cleanup this CPU thread object just yet. Put
+     * it on a list for later removal.
+     */
+    spapr_add_cpu_to_unplug_list(obj, unplug_list);
+    return 0;
+}
+
+static void spapr_core_release(DeviceState *dev, void *opaque)
+{
+    struct sPAPRCPUUnplugList unplug_list;
+    sPAPRMachineState *spapr = SPAPR_MACHINE(qdev_get_machine());
+    sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
+    char *slot = object_property_get_str(OBJECT(dev), CPU_CORE_SLOT_PROP,
+                 &error_fatal);
+
+    QLIST_INIT(&unplug_list);
+    object_child_foreach(OBJECT(dev), spapr_cpu_release, &unplug_list);
+    spapr_cpu_core_cleanup(&unplug_list);
+
+    /* Unset the link from machine object to this core */
+    object_property_set_link(OBJECT(spapr), NULL, slot, NULL);
+    g_free(slot);
+
+    g_free(core->threads);
+    object_unparent(OBJECT(dev));
+}
+
+void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
+                       Error **errp)
+{
+    sPAPRCPUCore *core = SPAPR_CPU_CORE(OBJECT(dev));
+    PowerPCCPU *cpu = &core->threads[0];
+    int id = ppc_get_vcpu_dt_id(cpu);
+    sPAPRDRConnector *drc =
+        spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
+    sPAPRDRConnectorClass *drck;
+    Error *local_err = NULL;
+
+    g_assert(drc);
+
+    drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
+    drck->detach(drc, dev, spapr_core_release, NULL, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
+        return;
+    }
+
+    spapr_hotplug_req_remove_by_index(drc);
+}
+
 static int spapr_cpu_core_realize_child(Object *child, void *opaque)
 {
     Error **errp = opaque;
diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index d1a0af8..8fab27b 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -593,6 +593,7 @@ void spapr_cpu_init(sPAPRMachineState *spapr, PowerPCCPU *cpu, Error **errp);
 void spapr_cpu_reset(void *opaque);
 void *spapr_populate_hotplug_cpu_dt(DeviceState *dev, CPUState *cs,
                                     int *fdt_offset, sPAPRMachineState *spapr);
+void spapr_cpu_destroy(PowerPCCPU *cpu);
 
 /* rtas-configure-connector state */
 struct sPAPRConfigureConnectorState {
diff --git a/include/hw/ppc/spapr_cpu_core.h b/include/hw/ppc/spapr_cpu_core.h
index 9879398..4638f96 100644
--- a/include/hw/ppc/spapr_cpu_core.h
+++ b/include/hw/ppc/spapr_cpu_core.h
@@ -28,4 +28,15 @@ typedef struct sPAPRCPUCore {
 
 void spapr_core_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                      Error **errp);
+void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
+                       Error **errp);
+
+/* List to store unplugged CPU objects for cleanup during unplug */
+typedef struct sPAPRCPUUnplug {
+    Object *cpu;
+    QLIST_ENTRY(sPAPRCPUUnplug) node;
+} sPAPRCPUUnplug;
+
+QLIST_HEAD(sPAPRCPUUnplugList, sPAPRCPUUnplug);
+
 #endif
-- 
2.1.0