[PATCH RFC V2 25/37] arm/virt: Add/update basic hot-(un)plug framework

[Salil Mehta]

Add CPU hot-unplug hooks and update hotplug hooks with additional sanity checks
for use in hotplug paths.

Note, Functional contents of the hooks(now left with TODO comment) shall be
gradually filled in the subsequent patches in an incremental approach to patch
and logic building which would be roughly as follows:
1. (Un-)wiring of interrupts between vCPU<->GIC
2. Sending events to Guest for hot-(un)plug so that guest can take appropriate
   actions.
3. Notifying GIC about hot-(un)plug action so that vCPU could be (un-)stitched
   to the GIC CPU interface.
4. Updating the Guest with Next boot info for this vCPU in the firmware.

Co-developed-by: Salil Mehta <salil.mehta@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
---
 hw/arm/virt.c | 104 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 104 insertions(+)

diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 3b068534a8..dce02136cb 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -81,6 +81,7 @@
 #include "hw/virtio/virtio-iommu.h"
 #include "hw/char/pl011.h"
 #include "qemu/guest-random.h"
+#include "qapi/qmp/qdict.h"
 
 #define DEFINE_VIRT_MACHINE_LATEST(major, minor, latest) \
     static void virt_##major##_##minor##_class_init(ObjectClass *oc, \
@@ -2985,12 +2986,23 @@ static void virt_cpu_pre_plug(HotplugHandler 
*hotplug_dev, DeviceState *dev,
 {
     VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
     MachineState *ms = MACHINE(hotplug_dev);
+    MachineClass *mc = MACHINE_GET_CLASS(ms);
     ARMCPU *cpu = ARM_CPU(dev);
     CPUState *cs = CPU(dev);
     CPUArchId *cpu_slot;
     int32_t min_cpuid = 0;
     int32_t max_cpuid;
 
+    if (dev->hotplugged && !vms->acpi_dev) {
+        error_setg(errp, "GED acpi device does not exists");
+        return;
+    }
+
+    if (dev->hotplugged && !mc->has_hotpluggable_cpus) {
+        error_setg(errp, "CPU hotplug not supported on this machine");
+        return;
+    }
+
     /* sanity check the cpu */
     if (!object_dynamic_cast(OBJECT(cpu), ms->cpu_type)) {
         error_setg(errp, "Invalid CPU type, expected cpu type: '%s'",
@@ -3039,6 +3051,22 @@ static void virt_cpu_pre_plug(HotplugHandler 
*hotplug_dev, DeviceState *dev,
     }
     virt_cpu_set_properties(OBJECT(cs), cpu_slot, errp);
 
+    /*
+     * Fix the GIC for this new vCPU being plugged. The QOM CPU object for the
+     * new vCPU need to be updated in the corresponding QOM GICv3CPUState 
object
+     * We also need to re-wire the IRQs for this new CPU object. This update
+     * is limited to the QOM only and does not affects the KVM. Later has
+     * already been pre-sized with possible CPU at VM init time. This is a
+     * workaround to the constraints posed by ARM architecture w.r.t supporting
+     * CPU Hotplug. Specification does not exist for the later.
+     * This patch-up is required both for {cold,hot}-plugged vCPUs. Cold-inited
+     * vCPUs have their GIC state initialized during machvit_init().
+     */
+    if (vms->acpi_dev) {
+        /* TODO: update GIC about this hotplug change here */
+        /* TODO: wire the GIC<->CPU irqs */
+    }
+
     /*
      * To give persistent presence view of vCPUs to the guest, ACPI might need
      * to fake the presence of the vCPUs to the guest but keep them disabled.
@@ -3050,6 +3078,7 @@ static void virt_cpu_pre_plug(HotplugHandler 
*hotplug_dev, DeviceState *dev,
 static void virt_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
                           Error **errp)
 {
+    VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
     MachineState *ms = MACHINE(hotplug_dev);
     CPUState *cs = CPU(dev);
     CPUArchId *cpu_slot;
@@ -3058,10 +3087,81 @@ static void virt_cpu_plug(HotplugHandler *hotplug_dev, 
DeviceState *dev,
     cpu_slot = virt_find_cpu_slot(ms, cs->cpu_index);
     cpu_slot->cpu = OBJECT(dev);
 
+    /*
+     * Update the ACPI Hotplug state both for vCPUs being {hot,cold}-plugged.
+     * vCPUs can be cold-plugged using '-device' option. For vCPUs being hot
+     * plugged, guest is also notified.
+     */
+    if (vms->acpi_dev) {
+        /* TODO: update acpi hotplug state. Send cpu hotplug event to guest */
+        /* TODO: register cpu for reset & update F/W info for the next boot */
+    }
+
     cs->disabled = false;
     return;
 }
 
+static void virt_cpu_unplug_request(HotplugHandler *hotplug_dev,
+                                    DeviceState *dev, Error **errp)
+{
+    MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
+    VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
+    ARMCPU *cpu = ARM_CPU(dev);
+    CPUState *cs = CPU(dev);
+
+    if (!vms->acpi_dev || !dev->realized) {
+        error_setg(errp, "GED does not exists or device is not realized!");
+        return;
+    }
+
+    if (!mc->has_hotpluggable_cpus) {
+        error_setg(errp, "CPU hot(un)plug not supported on this machine");
+        return;
+    }
+
+    if (cs->cpu_index == first_cpu->cpu_index) {
+        error_setg(errp, "Boot CPU(id%d=%d:%d:%d:%d) hot-unplug not supported",
+                   first_cpu->cpu_index, cpu->socket_id, cpu->cluster_id,
+                   cpu->core_id, cpu->thread_id);
+        return;
+    }
+
+    /* TODO: request cpu hotplug from guest */
+
+    return;
+}
+
+static void virt_cpu_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
+                            Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
+    MachineState *ms = MACHINE(hotplug_dev);
+    CPUState *cs = CPU(dev);
+    CPUArchId *cpu_slot;
+
+    if (!vms->acpi_dev || !dev->realized) {
+        error_setg(errp, "GED does not exists or device is not realized!");
+        return;
+    }
+
+    cpu_slot = virt_find_cpu_slot(ms, cs->cpu_index);
+
+    /* TODO: update the acpi cpu hotplug state for cpu hot-unplug */
+
+    /* TODO: unwire the gic-cpu irqs here */
+    /* TODO: update the GIC about this hot unplug change */
+
+    /* TODO: unregister cpu for reset & update F/W info for the next boot */
+
+    qobject_unref(dev->opts);
+    dev->opts = NULL;
+
+    cpu_slot->cpu = NULL;
+    cs->disabled = true;
+
+    return;
+}
+
 static void virt_machine_device_pre_plug_cb(HotplugHandler *hotplug_dev,
                                             DeviceState *dev, Error **errp)
 {
@@ -3185,6 +3285,8 @@ static void 
virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
         virtio_md_pci_unplug_request(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev),
                                      errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
+        virt_cpu_unplug_request(hotplug_dev, dev, errp);
     } else {
         error_setg(errp, "device unplug request for unsupported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
@@ -3198,6 +3300,8 @@ static void virt_machine_device_unplug_cb(HotplugHandler 
*hotplug_dev,
         virt_dimm_unplug(hotplug_dev, dev, errp);
     } else if (object_dynamic_cast(OBJECT(dev), TYPE_VIRTIO_MD_PCI)) {
         virtio_md_pci_unplug(VIRTIO_MD_PCI(dev), MACHINE(hotplug_dev), errp);
+    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
+        virt_cpu_unplug(hotplug_dev, dev, errp);
     } else {
         error_setg(errp, "virt: device unplug for unsupported device"
                    " type: %s", object_get_typename(OBJECT(dev)));
-- 
2.34.1