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

[Auger Eric <eric.auger@redhat.com>]

Hi Shameer,

On 3/18/20 1:37 PM, Shameer Kolothum wrote:
> This adds support for memory hot remove on arm/virt that
> uses acpi ged device.

I gave this a try and it works fine if the PCDIMM slot was initially
hotplugged:
(QEMU) object-add qom-type=memory-backend-ram id=mem1 props.size=4294967296
{"return": {}}
(QEMU) device_add driver=pc-dimm  id=pcdimm1 memdev=mem1
(QEMU) device_del id=pcdimm1
{"return": {}}

on guest I can see:
[   82.466321] Offlined Pages 262144
[   82.541712] Offlined Pages 262144
[   82.589236] Offlined Pages 262144
[   82.969166] Offlined Pages 262144

However I noticed that if qemu is launched directly with

-m 16G,maxmem=32G,slots=2 \
-object memory-backend-ram,id=mem1,size=4G \
-device pc-dimm,memdev=mem1,id=dimm1,driver=pc-dimm -device

and then in the qmp shell:
(QEMU) device_del id=dimm1

the hot-unplug fails in guest:

[   78.897407] Offlined Pages 262144
[   79.260811] Offlined Pages 262144
[   79.308105] Offlined Pages 262144
[   79.333675] page:fffffe00137d1f40 refcount:1 mapcount:0
mapping:ffff0004ea9f20b1 index:0xaaab11c6e
[   79.335927] anon flags: 0x17ffff8000080024(uptodate|active|swapbacked)
[   79.337571] raw: 17ffff8000080024 dead000000000100 dead000000000122
ffff0004ea9f20b1
[   79.339502] raw: 0000000aaab11c6e 0000000000000000 00000001ffffffff
ffff0004fd4e3000
[   79.341701] page dumped because: unmovable page
[   79.342887] page->mem_cgroup:ffff0004fd4e3000
[   79.354729] page:fffffe00137d1f40 refcount:1 mapcount:0
mapping:ffff0004ea9f20b1 index:0xaaab11c6e
[   79.357012] anon flags: 0x17ffff8000080024(uptodate|active|swapbacked)
[   79.358658] raw: 17ffff8000080024 dead000000000100 dead000000000122
ffff0004ea9f20b1
[   79.360611] raw: 0000000aaab11c6e 0000000000000000 00000001ffffffff
ffff0004fd4e3000
[   79.362560] page dumped because: unmovable page
[   79.363742] page->mem_cgroup:ffff0004fd4e3000
[   79.368636] memory memory20: Offline failed.

I did not expect this. The PCDIMM slot in that case does not seem to be
interpreted as a hot-unpluggable one (?). I added Anshuman in cc.

Thanks

Eric



> 
> 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";
>