[RFC v1] arm/virt: Add memory hot remove support

[Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>]

This adds support for memory hot remove on arm/virt that
uses acpi ged device.

Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
---
 -RFC because linux kernel support for mem hot remove is just queued
  for 5.7[1].
 -Tested with guest kernel 5.6-rc5 + [1]

1. https://patchwork.kernel.org/cover/11419301/
---
 hw/acpi/generic_event_device.c | 28 +++++++++++++++++
 hw/arm/virt.c                  | 56 ++++++++++++++++++++++++++++++++--
 2 files changed, 82 insertions(+), 2 deletions(-)

diff --git a/hw/acpi/generic_event_device.c b/hw/acpi/generic_event_device.c
index 021ed2bf23..3e28c110fa 100644
--- a/hw/acpi/generic_event_device.c
+++ b/hw/acpi/generic_event_device.c
@@ -182,6 +182,32 @@ static void acpi_ged_device_plug_cb(HotplugHandler *hotplug_dev,
     }
 }
 
+static void acpi_ged_unplug_request_cb(HotplugHandler *hotplug_dev,
+                                       DeviceState *dev, Error **errp)
+{
+    AcpiGedState *s = ACPI_GED(hotplug_dev);
+
+    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
+        acpi_memory_unplug_request_cb(hotplug_dev, &s->memhp_state, dev, errp);
+    } else {
+        error_setg(errp, "acpi: device unplug request for unsupported device"
+                   " type: %s", object_get_typename(OBJECT(dev)));
+    }
+}
+
+static void acpi_ged_unplug_cb(HotplugHandler *hotplug_dev,
+                               DeviceState *dev, Error **errp)
+{
+    AcpiGedState *s = ACPI_GED(hotplug_dev);
+
+    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
+        acpi_memory_unplug_cb(&s->memhp_state, dev, errp);
+    } else {
+        error_setg(errp, "acpi: device unplug for unsupported device"
+                   " type: %s", object_get_typename(OBJECT(dev)));
+    }
+}
+
 static void acpi_ged_send_event(AcpiDeviceIf *adev, AcpiEventStatusBits ev)
 {
     AcpiGedState *s = ACPI_GED(adev);
@@ -286,6 +312,8 @@ static void acpi_ged_class_init(ObjectClass *class, void *data)
     dc->vmsd = &vmstate_acpi_ged;
 
     hc->plug = acpi_ged_device_plug_cb;
+    hc->unplug_request = acpi_ged_unplug_request_cb;
+    hc->unplug = acpi_ged_unplug_cb;
 
     adevc->send_event = acpi_ged_send_event;
 }
diff --git a/hw/arm/virt.c b/hw/arm/virt.c
index 94f93dda54..91974e4e80 100644
--- a/hw/arm/virt.c
+++ b/hw/arm/virt.c
@@ -2096,11 +2096,62 @@ static void virt_machine_device_plug_cb(HotplugHandler *hotplug_dev,
     }
 }
 
+static void virt_dimm_unplug_request(HotplugHandler *hotplug_dev,
+                                     DeviceState *dev, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
+    Error *local_err = NULL;
+
+    if (!vms->acpi_dev) {
+        error_setg(errp,
+                   "memory hotplug is not enabled: missing acpi-ged device");
+        goto out;
+    }
+
+    hotplug_handler_unplug_request(HOTPLUG_HANDLER(vms->acpi_dev), dev,
+                                   &local_err);
+out:
+    error_propagate(errp, local_err);
+}
+
+static void virt_dimm_unplug(HotplugHandler *hotplug_dev,
+                             DeviceState *dev, Error **errp)
+{
+    VirtMachineState *vms = VIRT_MACHINE(hotplug_dev);
+    Error *local_err = NULL;
+
+    hotplug_handler_unplug(HOTPLUG_HANDLER(vms->acpi_dev), dev, &local_err);
+    if (local_err) {
+        goto out;
+    }
+
+    pc_dimm_unplug(PC_DIMM(dev), MACHINE(vms));
+    object_property_set_bool(OBJECT(dev), false, "realized", NULL);
+
+ out:
+    error_propagate(errp, local_err);
+}
+
 static void virt_machine_device_unplug_request_cb(HotplugHandler *hotplug_dev,
                                           DeviceState *dev, Error **errp)
 {
-    error_setg(errp, "device unplug request for unsupported device"
-               " type: %s", object_get_typename(OBJECT(dev)));
+    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
+        virt_dimm_unplug_request(hotplug_dev, dev, errp);
+    } else {
+        error_setg(errp, "device unplug request for unsupported device"
+                   " type: %s", object_get_typename(OBJECT(dev)));
+    }
+}
+
+static void virt_machine_device_unplug_cb(HotplugHandler *hotplug_dev,
+                                          DeviceState *dev, Error **errp)
+{
+    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
+        virt_dimm_unplug(hotplug_dev, dev, errp);
+    } else {
+        error_setg(errp, "virt: device unplug for unsupported device"
+                   " type: %s", object_get_typename(OBJECT(dev)));
+    }
 }
 
 static HotplugHandler *virt_machine_get_hotplug_handler(MachineState *machine,
@@ -2181,6 +2232,7 @@ static void virt_machine_class_init(ObjectClass *oc, void *data)
     hc->pre_plug = virt_machine_device_pre_plug_cb;
     hc->plug = virt_machine_device_plug_cb;
     hc->unplug_request = virt_machine_device_unplug_request_cb;
+    hc->unplug = virt_machine_device_unplug_cb;
     mc->numa_mem_supported = true;
     mc->auto_enable_numa_with_memhp = true;
     mc->default_ram_id = "mach-virt.ram";
-- 
2.17.1