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

[Wei Yang <richard.weiyang@gmail.com>]

On Fri, Feb 15, 2019 at 12:14:32PM +0100, Igor Mammedov wrote:
>On Thu, 14 Feb 2019 20:53:31 +0000
>Wei Yang <richard.weiyang@gmail.com> wrote:
>
>> On Thu, Feb 14, 2019 at 12:25:27PM +0100, Igor Mammedov wrote:
>> >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.
>> >
>> 
>> Thanks Igor, I rephrase above change log like this. Does this look
>> better to you now?
>> 
>>     Before we do device realization and plug, we would allocate
>s/would/should/
>
>>     necessary resources and check if memory-hotplug-support property is
>>     enabled.
>>     
>>     In piix4 and ich9, the acpi_memory_hotplug property is checked in
>s/in/at the/
>>     plug stage, this doesn't comply with current architecture. This
>drop              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>>     means we have prepared everything and even do pc_dimm_plug()
>            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>that device has been realized and mapped into guest address space
>'pc_dimm_plug()' by the time acpi plug handler is called, where it might
>fail and crash QEMU due to reaching  g_assert_not_reached() (piix4) or
>error_abort (ich9).
>
>or something like this, I'm not native speaker either so CC Eric Blake
>on next respin so he could check commit message.
>

Thanks for your patience and detailed suggestion :-)

>>     successfuly, but failed at last because
>>     acpi_memory_hotplug.is_enabled == false. Which is worse is in piix4,
>>     this endup at g_assert_not_reached() and cause QEMU crash.
>> 
>> 
>> >> 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)?
>> >
>> 
>> You are right, I missed this part.
>> 
>> >>  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
>> >
>> 
>> Thanks, will fix this.
>> 
>> >>      if (is_nvdimm && !pcms->acpi_nvdimm_state.is_enabled) {
>> >>          error_setg(errp, "nvdimm is not enabled: missing 'nvdimm' in '-M'");
>> >>          return;
>> >
>> 

-- 
Wei Yang
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