Re: [Qemu-devel] [PATCH] i386, acpi: check acpi_memory_hotplug capacity in pre_plug

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 14 Feb 2019 08:52:25 +0800
Wei Yang <richardw.yang@linux.intel.com> wrote:

> Currently we do device realization like below:
> 
>    hotplug_handler_pre_plug()
>    dc->realize()
>    hotplug_handler_plug()
> 
> Before we do device realization and plug, we would allocate necessary
> resources and check the capacity.
'capacity' probably is not right word to use here
maybe s/the capacity/if 'memory-hotplug-support' property is enabled/

> 
> While we leave acpi_memory_hotplug capacity check in the last step. This
wouldn't use 'leave' and 'capacity' here either, pls rephrase.

> looks not comply with current architecture and does some unnecessary
s/looks not/doesn't/
> work.
add more explanation about 'unnecessary work'.
problem as I see it, is that after successful pc_dimm_plug()
we get into piix4_device_plug_cb() and since
 s->acpi_memory_hotplug.is_enabled == false
and all other 'if' conditions also false we would endup
at g_assert_not_reached() causing QEMU crash in piix4 case
and with error_abort up the call chain in case of ich9.

> This patch abstract the check on acpi_memory_hotplug capacity in
> pre_plug stage.
> 
> Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
> ---
>  hw/acpi/piix4.c | 14 ++++++++++++--
>  hw/i386/pc.c    |  8 ++++++++
doesn't look complete, why did you skip on similar code in ich9
(Q35 machine)?

>  2 files changed, 20 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> index e330f24c71..c97b747496 100644
> --- a/hw/acpi/piix4.c
> +++ b/hw/acpi/piix4.c
> @@ -370,13 +370,22 @@ static void piix4_pm_powerdown_req(Notifier *n, void *opaque)
>      acpi_pm1_evt_power_down(&s->ar);
>  }
>  
> +static void piix4_device_pre_plug_cb(HotplugHandler *hotplug_dev,
> +                                 DeviceState *dev, Error **errp)
> +{
> +    PIIX4PMState *s = PIIX4_PM(hotplug_dev);
> +
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) &&
> +        !s->acpi_memory_hotplug.is_enabled)
> +        error_setg(errp,
> +            "memory hotplug is not enabled: PIIX4 memory hotplug disabled");
> +}
>  static void piix4_device_plug_cb(HotplugHandler *hotplug_dev,
>                                   DeviceState *dev, Error **errp)
>  {
>      PIIX4PMState *s = PIIX4_PM(hotplug_dev);
>  
> -    if (s->acpi_memory_hotplug.is_enabled &&
> -        object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
> +    if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
>          if (object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM)) {
>              nvdimm_acpi_plug_cb(hotplug_dev, dev);
>          } else {
> @@ -702,6 +711,7 @@ static void piix4_pm_class_init(ObjectClass *klass, void *data)
>       */
>      dc->user_creatable = false;
>      dc->hotpluggable = false;
> +    hc->pre_plug = piix4_device_pre_plug_cb;
>      hc->plug = piix4_device_plug_cb;
>      hc->unplug_request = piix4_device_unplug_request_cb;
>      hc->unplug = piix4_device_unplug_cb;
> diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> index 734d3268fa..3c6eed0cd3 100644
> --- a/hw/i386/pc.c
> +++ b/hw/i386/pc.c
> @@ -1662,6 +1662,7 @@ static void pc_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>      const PCMachineClass *pcmc = PC_MACHINE_GET_CLASS(pcms);
>      const bool is_nvdimm = object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM);
>      const uint64_t legacy_align = TARGET_PAGE_SIZE;
> +    HotplugHandlerClass *hhc;
>  
>      /*
>       * When -no-acpi is used with Q35 machine type, no ACPI is built,
> @@ -1674,6 +1675,13 @@ static void pc_memory_pre_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
>          return;
>      }
>  
> +    /*
> +     * Check acpi_dev memory hotplug capacity
> +     */
> +    hhc = HOTPLUG_HANDLER_GET_CLASS(pcms->acpi_dev);
> +    if (hcc->pre_plug)
> +        hhc->pre_plug(HOTPLUG_HANDLER(pcms->acpi_dev), dev, errp);
use hotplug_handler_pre_plug() instead of open-coding check

>      if (is_nvdimm && !pcms->acpi_nvdimm_state.is_enabled) {
>          error_setg(errp, "nvdimm is not enabled: missing 'nvdimm' in '-M'");
>          return;