RE: [PATCH v4] arm/virt: Add memory hot remove support

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

> -----Original Message-----
> From: Igor Mammedov [mailto:imammedo@redhat.com]
> Sent: 24 June 2020 15:09
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
> Cc: qemu-devel@nongnu.org; qemu-arm@nongnu.org;
> peter.maydell@linaro.org; mst@redhat.com; Linuxarm
> <linuxarm@huawei.com>; xuwei (O) <xuwei5@huawei.com>;
> eric.auger@redhat.com; Zengtao (B) <prime.zeng@hisilicon.com>
> Subject: Re: [PATCH v4] arm/virt: Add memory hot remove support
> 
> On Mon, 22 Jun 2020 13:41:57 +0100
> Shameer Kolothum <shameerali.kolothum.thodi@huawei.com> wrote:
> 
> > This adds support for memory(pc-dimm) hot remove on arm/virt that
> > uses acpi ged device.
> >
> > NVDIMM hot removal is not yet supported.
> >
> > Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
> > ---
> > v2 --> v3
> >   -Addressed Eric's comments on v3.
> > v2 --> v3
> >   -Addressed Eric's review comment and added check for NVDIMM.
> > RFC v1 --> v2
> >   -Rebased on top of latest Qemu master.
> >   -Dropped "RFC" and tested with kernel 5.7-rc6
> > ---
> >  hw/acpi/generic_event_device.c | 29 ++++++++++++++++
> >  hw/arm/virt.c                  | 62
> ++++++++++++++++++++++++++++++++--
> >  2 files changed, 89 insertions(+), 2 deletions(-)
> >
> > diff --git a/hw/acpi/generic_event_device.c
> b/hw/acpi/generic_event_device.c
> > index 1cb34111e5..b8abdefa1c 100644
> > --- a/hw/acpi/generic_event_device.c
> > +++ b/hw/acpi/generic_event_device.c
> > @@ -193,6 +193,33 @@ static void

[...]

> > +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));
> > +    qdev_unrealize(dev);
> 
> doesn't pc_dimm_unplug() do unrealize already?
> (/me wonders why it doesn't explode here,
> are we leaking a refference somewhere so dimm is still alive?)

Does it? From a quick look at the code it is not obvious.

pc_dimm_unplug()
  memory_device_unplug()
    memory_region_del_subregion()
  vmstate_unregister_ram()
    qemu_ram_unset_idstr()
    qemu_ram_unset_migratable()

If it does, then we may need to fix x86/ppc as well.

Thanks,
Shameer

> > +
> > +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,
> > @@ -2262,6 +2319,7 @@ 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->nvdimm_supported = true;
> >      mc->auto_enable_numa_with_memhp = true;