Re: [PATCH V15 3/7] hw/acpi: Update ACPI GED framework to support vCPU Hotplug

[Igor Mammedov <imammedo@redhat.com>]

On Sat, 13 Jul 2024 19:25:12 +0100
Salil Mehta <salil.mehta@huawei.com> wrote:

> ACPI GED (as described in the ACPI 6.4 spec) uses an interrupt listed in the
> _CRS object of GED to intimate OSPM about an event. Later then demultiplexes the
> notified event by evaluating ACPI _EVT method to know the type of event. Use
> ACPI GED to also notify the guest kernel about any CPU hot(un)plug events.
> 
> Note, GED interface is used by many hotplug events like memory hotplug, NVDIMM
> hotplug and non-hotplug events like system power down event. Each of these can
> be selected using a bit in the 32 bit GED IO interface. A bit has been reserved
> for the CPU hotplug event.

> ACPI CPU hotplug related initialization should only happen if ACPI_CPU_HOTPLUG
> support has been enabled for particular architecture. Add cpu_hotplug_hw_init()
> stub to avoid compilation break.

so any target (and machines in it) that has ACPI_CPU_HOTPLUG enabled will use have all CPU hotplug
machinery builtin which is fine.

However any machine that uses GED but do not opt-in into CPU hotplug,
will still have CPU hotplug registers/memory regions enabled/mapped. 

It's not much concern for upstream as migration from new to older QEMU
is not supported, however it will break migration downstream (arm/virt) as
new QEMU will try to migrate memory regions/state that do not exists
in older QEMU. Se below for suggestion.

> 
> Co-developed-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Keqian Zhu <zhukeqian1@huawei.com>
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> Reviewed-by: Gavin Shan <gshan@redhat.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Shaoqin Huang <shahuang@redhat.com>
> Tested-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Xianglai Li <lixianglai@loongson.cn>
> Tested-by: Miguel Luis <miguel.luis@oracle.com>
> Reviewed-by: Vishnu Pajjuri <vishnu@os.amperecomputing.com>
> Tested-by: Zhao Liu <zhao1.liu@intel.com>
> Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
> ---
>  docs/specs/acpi_hw_reduced_hotplug.rst |  3 ++-
>  hw/acpi/acpi-cpu-hotplug-stub.c        |  6 ++++++
>  hw/acpi/generic_event_device.c         | 24 ++++++++++++++++++++++++
>  include/hw/acpi/generic_event_device.h |  4 ++++
>  4 files changed, 36 insertions(+), 1 deletion(-)
> 
> diff --git a/docs/specs/acpi_hw_reduced_hotplug.rst b/docs/specs/acpi_hw_reduced_hotplug.rst
> index 0bd3f9399f..3acd6fcd8b 100644
> --- a/docs/specs/acpi_hw_reduced_hotplug.rst
> +++ b/docs/specs/acpi_hw_reduced_hotplug.rst
> @@ -64,7 +64,8 @@ GED IO interface (4 byte access)
>         0: Memory hotplug event
>         1: System power down event
>         2: NVDIMM hotplug event
> -    3-31: Reserved
> +       3: CPU hotplug event
> +    4-31: Reserved
>  
>  **write_access:**
>  
> diff --git a/hw/acpi/acpi-cpu-hotplug-stub.c b/hw/acpi/acpi-cpu-hotplug-stub.c
> index 3fc4b14c26..c6c61bb9cd 100644
> --- a/hw/acpi/acpi-cpu-hotplug-stub.c
> +++ b/hw/acpi/acpi-cpu-hotplug-stub.c
> @@ -19,6 +19,12 @@ void legacy_acpi_cpu_hotplug_init(MemoryRegion *parent, Object *owner,
>      return;
>  }
>  
> +void cpu_hotplug_hw_init(MemoryRegion *as, Object *owner,
> +                         CPUHotplugState *state, hwaddr base_addr)
> +{
> +    return;
> +}
> +
>  void acpi_cpu_ospm_status(CPUHotplugState *cpu_st, ACPIOSTInfoList ***list)
>  {
>      return;
> diff --git a/hw/acpi/generic_event_device.c b/hw/acpi/generic_event_device.c
> index 2d6e91b124..1b31d633ba 100644
> --- a/hw/acpi/generic_event_device.c
> +++ b/hw/acpi/generic_event_device.c
> @@ -25,6 +25,7 @@ static const uint32_t ged_supported_events[] = {
>      ACPI_GED_MEM_HOTPLUG_EVT,
>      ACPI_GED_PWR_DOWN_EVT,
>      ACPI_GED_NVDIMM_HOTPLUG_EVT,
> +    ACPI_GED_CPU_HOTPLUG_EVT,
>  };
>  
>  /*
> @@ -234,6 +235,8 @@ static void acpi_ged_device_plug_cb(HotplugHandler *hotplug_dev,
>          } else {
>              acpi_memory_plug_cb(hotplug_dev, &s->memhp_state, dev, errp);
>          }
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        acpi_cpu_plug_cb(hotplug_dev, &s->cpuhp_state, dev, errp);
>      } else {
>          error_setg(errp, "virt: device plug request for unsupported device"
>                     " type: %s", object_get_typename(OBJECT(dev)));
> @@ -248,6 +251,8 @@ static void acpi_ged_unplug_request_cb(HotplugHandler *hotplug_dev,
>      if ((object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM) &&
>                         !(object_dynamic_cast(OBJECT(dev), TYPE_NVDIMM)))) {
>          acpi_memory_unplug_request_cb(hotplug_dev, &s->memhp_state, dev, errp);
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        acpi_cpu_unplug_request_cb(hotplug_dev, &s->cpuhp_state, dev, errp);
>      } else {
>          error_setg(errp, "acpi: device unplug request for unsupported device"
>                     " type: %s", object_get_typename(OBJECT(dev)));
> @@ -261,6 +266,8 @@ static void acpi_ged_unplug_cb(HotplugHandler *hotplug_dev,
>  
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
>          acpi_memory_unplug_cb(&s->memhp_state, dev, errp);
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> +        acpi_cpu_unplug_cb(&s->cpuhp_state, dev, errp);
>      } else {
>          error_setg(errp, "acpi: device unplug for unsupported device"
>                     " type: %s", object_get_typename(OBJECT(dev)));
> @@ -272,6 +279,7 @@ static void acpi_ged_ospm_status(AcpiDeviceIf *adev, ACPIOSTInfoList ***list)
>      AcpiGedState *s = ACPI_GED(adev);
>  
>      acpi_memory_ospm_status(&s->memhp_state, list);
> +    acpi_cpu_ospm_status(&s->cpuhp_state, list);
>  }
>  
>  static void acpi_ged_send_event(AcpiDeviceIf *adev, AcpiEventStatusBits ev)
> @@ -286,6 +294,8 @@ static void acpi_ged_send_event(AcpiDeviceIf *adev, AcpiEventStatusBits ev)
>          sel = ACPI_GED_PWR_DOWN_EVT;
>      } else if (ev & ACPI_NVDIMM_HOTPLUG_STATUS) {
>          sel = ACPI_GED_NVDIMM_HOTPLUG_EVT;
> +    } else if (ev & ACPI_CPU_HOTPLUG_STATUS) {
> +        sel = ACPI_GED_CPU_HOTPLUG_EVT;
>      } else {
>          /* Unknown event. Return without generating interrupt. */
>          warn_report("GED: Unsupported event %d. No irq injected", ev);
> @@ -371,6 +381,19 @@ static const VMStateDescription vmstate_acpi_ged = {
>      }
>  };
>  
> +static void acpi_ged_realize(DeviceState *dev, Error **errp)
> +{
> +    AcpiGedState *s = ACPI_GED(dev);
> +    SysBusDevice *sbd = SYS_BUS_DEVICE(dev);
> +

> +    /* initialize CPU Hotplug related regions */
> +    memory_region_init(&s->container_cpuhp, OBJECT(dev), "cpuhp container",
> +                       ACPI_CPU_HOTPLUG_REG_LEN);
> +    sysbus_init_mmio(sbd, &s->container_cpuhp);
> +    cpu_hotplug_hw_init(&s->container_cpuhp, OBJECT(dev),
> +                        &s->cpuhp_state, 0);

how about making it conditional on supported events
see hw/arm/virt.c: create_acpi_ged()
    if (ms->ram_slots) {                                                         
        event |= ACPI_GED_MEM_HOTPLUG_EVT;                                       
    }                                                                            
                                                                                 
    if (ms->nvdimms_state->is_enabled) {                                         
        event |= ACPI_GED_NVDIMM_HOTPLUG_EVT;                                    
    } 

so cpu hotplug would have similar section
and ged realize could use ged-event to enable/disable
cpuhp feature registers and hwinit.

> +}
> +
>  static void acpi_ged_initfn(Object *obj)
>  {
>      DeviceState *dev = DEVICE(obj);
> @@ -411,6 +434,7 @@ static void acpi_ged_class_init(ObjectClass *class, void *data)
>      dc->desc = "ACPI Generic Event Device";
>      device_class_set_props(dc, acpi_ged_properties);
>      dc->vmsd = &vmstate_acpi_ged;
> +    dc->realize = acpi_ged_realize;
>  
>      hc->plug = acpi_ged_device_plug_cb;
>      hc->unplug_request = acpi_ged_unplug_request_cb;
> diff --git a/include/hw/acpi/generic_event_device.h b/include/hw/acpi/generic_event_device.h
> index ba84ce0214..e091ac2108 100644
> --- a/include/hw/acpi/generic_event_device.h
> +++ b/include/hw/acpi/generic_event_device.h
> @@ -62,6 +62,7 @@
>  #include "hw/sysbus.h"
>  #include "hw/acpi/memory_hotplug.h"
>  #include "hw/acpi/ghes.h"
> +#include "hw/acpi/cpu.h"
>  #include "qom/object.h"
>  
>  #define ACPI_POWER_BUTTON_DEVICE "PWRB"
> @@ -95,6 +96,7 @@ OBJECT_DECLARE_SIMPLE_TYPE(AcpiGedState, ACPI_GED)
>  #define ACPI_GED_MEM_HOTPLUG_EVT   0x1
>  #define ACPI_GED_PWR_DOWN_EVT      0x2
>  #define ACPI_GED_NVDIMM_HOTPLUG_EVT 0x4
> +#define ACPI_GED_CPU_HOTPLUG_EVT    0x8
>  
>  typedef struct GEDState {
>      MemoryRegion evt;
> @@ -106,6 +108,8 @@ struct AcpiGedState {
>      SysBusDevice parent_obj;
>      MemHotplugState memhp_state;
>      MemoryRegion container_memhp;
> +    CPUHotplugState cpuhp_state;
> +    MemoryRegion container_cpuhp;
>      GEDState ged_state;
>      uint32_t ged_event_bitmap;
>      qemu_irq irq;