Re: [PATCH v5 04/28] hw/i386/pc: Remove PCMachineClass::legacy_cpu_hotplug field

[Igor Mammedov <imammedo@redhat.com>]

On Wed,  3 Dec 2025 00:28:11 +0800
Zhao Liu <zhao1.liu@intel.com> wrote:

> From: Philippe Mathieu-Daudé <philmd@linaro.org>
> 
> Now all PC & Q35 machiens are using modern hotplug from the beginning,
> and all legacy_cpu_hotplug flags keep false during runtime.
> 
> So it's safe to remove legacy_cpu_hotplug flags and related properties,
> with unused gpe_cpu field.
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> Signed-off-by: Zhao Liu <zhao1.liu@intel.com>

Acked-by: Igor Mammedov <imammedo@redhat.com>

> ---
> Changes since v4:
>  * Referring Igor's v5 [*], drop gpe_cpu field and does not only remove
>    build_legacy_cpu_hotplug_aml(), but instead remove the entire
>    cpu_hotplug.c file in a separate patch.
> 
> [*]: https://lore.kernel.org/qemu-devel/20251031142825.179239-1-imammedo@redhat.com/
> ---
>  hw/acpi/ich9.c          | 40 ++++------------------------------------
>  hw/acpi/piix4.c         | 40 ++++------------------------------------
>  hw/i386/acpi-build.c    |  4 +---
>  include/hw/acpi/ich9.h  |  2 --
>  include/hw/acpi/piix4.h |  2 --
>  include/hw/i386/pc.h    |  3 ---
>  6 files changed, 9 insertions(+), 82 deletions(-)
> 
> diff --git a/hw/acpi/ich9.c b/hw/acpi/ich9.c
> index 54590129c695..f254f3879716 100644
> --- a/hw/acpi/ich9.c
> +++ b/hw/acpi/ich9.c
> @@ -339,26 +339,6 @@ static void ich9_pm_get_gpe0_blk(Object *obj, Visitor *v, const char *name,
>      visit_type_uint32(v, name, &value, errp);
>  }
>  
> -static bool ich9_pm_get_cpu_hotplug_legacy(Object *obj, Error **errp)
> -{
> -    ICH9LPCState *s = ICH9_LPC_DEVICE(obj);
> -
> -    return s->pm.cpu_hotplug_legacy;
> -}
> -
> -static void ich9_pm_set_cpu_hotplug_legacy(Object *obj, bool value,
> -                                           Error **errp)
> -{
> -    ICH9LPCState *s = ICH9_LPC_DEVICE(obj);
> -
> -    assert(!value);
> -    if (s->pm.cpu_hotplug_legacy && value == false) {
> -        acpi_switch_to_modern_cphp(&s->pm.gpe_cpu, &s->pm.cpuhp_state,
> -                                   ICH9_CPU_HOTPLUG_IO_BASE);
> -    }
> -    s->pm.cpu_hotplug_legacy = value;
> -}
> -
>  static bool ich9_pm_get_enable_tco(Object *obj, Error **errp)
>  {
>      ICH9LPCState *s = ICH9_LPC_DEVICE(obj);
> @@ -403,7 +383,6 @@ void ich9_pm_add_properties(Object *obj, ICH9LPCPMRegs *pm)
>  {
>      static const uint32_t gpe0_len = ICH9_PMIO_GPE0_LEN;
>      pm->acpi_memory_hotplug.is_enabled = true;
> -    pm->cpu_hotplug_legacy = false;
>      pm->disable_s3 = 0;
>      pm->disable_s4 = 0;
>      pm->s4_val = 2;
> @@ -422,9 +401,6 @@ void ich9_pm_add_properties(Object *obj, ICH9LPCPMRegs *pm)
>                          NULL, NULL, pm);
>      object_property_add_uint32_ptr(obj, ACPI_PM_PROP_GPE0_BLK_LEN,
>                                     &gpe0_len, OBJ_PROP_FLAG_READ);
> -    object_property_add_bool(obj, "cpu-hotplug-legacy",
> -                             ich9_pm_get_cpu_hotplug_legacy,
> -                             ich9_pm_set_cpu_hotplug_legacy);
>      object_property_add_uint8_ptr(obj, ACPI_PM_PROP_S3_DISABLED,
>                                    &pm->disable_s3, OBJ_PROP_FLAG_READWRITE);
>      object_property_add_uint8_ptr(obj, ACPI_PM_PROP_S4_DISABLED,
> @@ -477,11 +453,7 @@ void ich9_pm_device_plug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
>                                  dev, errp);
>          }
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> -        if (lpc->pm.cpu_hotplug_legacy) {
> -            legacy_acpi_cpu_plug_cb(hotplug_dev, &lpc->pm.gpe_cpu, dev, errp);
> -        } else {
> -            acpi_cpu_plug_cb(hotplug_dev, &lpc->pm.cpuhp_state, dev, errp);
> -        }
> +        acpi_cpu_plug_cb(hotplug_dev, &lpc->pm.cpuhp_state, dev, errp);
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
>          acpi_pcihp_device_plug_cb(hotplug_dev, &lpc->pm.acpi_pci_hotplug,
>                                    dev, errp);
> @@ -500,8 +472,7 @@ void ich9_pm_device_unplug_request_cb(HotplugHandler *hotplug_dev,
>          acpi_memory_unplug_request_cb(hotplug_dev,
>                                        &lpc->pm.acpi_memory_hotplug, dev,
>                                        errp);
> -    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) &&
> -               !lpc->pm.cpu_hotplug_legacy) {
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
>          uint64_t negotiated = lpc->smi_negotiated_features;
>  
>          if (negotiated & BIT_ULL(ICH9_LPC_SMI_F_BROADCAST_BIT) &&
> @@ -533,8 +504,7 @@ void ich9_pm_device_unplug_cb(HotplugHandler *hotplug_dev, DeviceState *dev,
>  
>      if (object_dynamic_cast(OBJECT(dev), TYPE_PC_DIMM)) {
>          acpi_memory_unplug_cb(&lpc->pm.acpi_memory_hotplug, dev, errp);
> -    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) &&
> -               !lpc->pm.cpu_hotplug_legacy) {
> +    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
>          acpi_cpu_unplug_cb(&lpc->pm.cpuhp_state, dev, errp);
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
>          acpi_pcihp_device_unplug_cb(hotplug_dev, &lpc->pm.acpi_pci_hotplug,
> @@ -556,7 +526,5 @@ void ich9_pm_ospm_status(AcpiDeviceIf *adev, ACPIOSTInfoList ***list)
>      ICH9LPCState *s = ICH9_LPC_DEVICE(adev);
>  
>      acpi_memory_ospm_status(&s->pm.acpi_memory_hotplug, list);
> -    if (!s->pm.cpu_hotplug_legacy) {
> -        acpi_cpu_ospm_status(&s->pm.cpuhp_state, list);
> -    }
> +    acpi_cpu_ospm_status(&s->pm.cpuhp_state, list);
>  }
> diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
> index a7a29b0d09a9..6ad5f1d1c19d 100644
> --- a/hw/acpi/piix4.c
> +++ b/hw/acpi/piix4.c
> @@ -336,11 +336,7 @@ static void piix4_device_plug_cb(HotplugHandler *hotplug_dev,
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
>          acpi_pcihp_device_plug_cb(hotplug_dev, &s->acpi_pci_hotplug, dev, errp);
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU)) {
> -        if (s->cpu_hotplug_legacy) {
> -            legacy_acpi_cpu_plug_cb(hotplug_dev, &s->gpe_cpu, dev, errp);
> -        } else {
> -            acpi_cpu_plug_cb(hotplug_dev, &s->cpuhp_state, dev, errp);
> -        }
> +        acpi_cpu_plug_cb(hotplug_dev, &s->cpuhp_state, dev, errp);
>      } else {
>          g_assert_not_reached();
>      }
> @@ -358,8 +354,7 @@ static void piix4_device_unplug_request_cb(HotplugHandler *hotplug_dev,
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
>          acpi_pcihp_device_unplug_request_cb(hotplug_dev, &s->acpi_pci_hotplug,
>                                              dev, errp);
> -    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) &&
> -               !s->cpu_hotplug_legacy) {
> +    } 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 not supported device"
> @@ -378,8 +373,7 @@ static void piix4_device_unplug_cb(HotplugHandler *hotplug_dev,
>      } else if (object_dynamic_cast(OBJECT(dev), TYPE_PCI_DEVICE)) {
>          acpi_pcihp_device_unplug_cb(hotplug_dev, &s->acpi_pci_hotplug, dev,
>                                      errp);
> -    } else if (object_dynamic_cast(OBJECT(dev), TYPE_CPU) &&
> -               !s->cpu_hotplug_legacy) {
> +    } 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 not supported device"
> @@ -523,26 +517,6 @@ static const MemoryRegionOps piix4_gpe_ops = {
>      .endianness = DEVICE_LITTLE_ENDIAN,
>  };
>  
> -
> -static bool piix4_get_cpu_hotplug_legacy(Object *obj, Error **errp)
> -{
> -    PIIX4PMState *s = PIIX4_PM(obj);
> -
> -    return s->cpu_hotplug_legacy;
> -}
> -
> -static void piix4_set_cpu_hotplug_legacy(Object *obj, bool value, Error **errp)
> -{
> -    PIIX4PMState *s = PIIX4_PM(obj);
> -
> -    assert(!value);
> -    if (s->cpu_hotplug_legacy && value == false) {
> -        acpi_switch_to_modern_cphp(&s->gpe_cpu, &s->cpuhp_state,
> -                                   PIIX4_CPU_HOTPLUG_IO_BASE);
> -    }
> -    s->cpu_hotplug_legacy = value;
> -}
> -
>  static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
>                                             PCIBus *bus, PIIX4PMState *s)
>  {
> @@ -558,10 +532,6 @@ static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
>          qbus_set_hotplug_handler(BUS(pci_get_bus(PCI_DEVICE(s))), OBJECT(s));
>      }
>  
> -    s->cpu_hotplug_legacy = false;
> -    object_property_add_bool(OBJECT(s), "cpu-hotplug-legacy",
> -                             piix4_get_cpu_hotplug_legacy,
> -                             piix4_set_cpu_hotplug_legacy);
>      cpu_hotplug_hw_init(parent, OBJECT(s), &s->cpuhp_state,
>                          PIIX4_CPU_HOTPLUG_IO_BASE);
>  
> @@ -576,9 +546,7 @@ static void piix4_ospm_status(AcpiDeviceIf *adev, ACPIOSTInfoList ***list)
>      PIIX4PMState *s = PIIX4_PM(adev);
>  
>      acpi_memory_ospm_status(&s->acpi_memory_hotplug, list);
> -    if (!s->cpu_hotplug_legacy) {
> -        acpi_cpu_ospm_status(&s->cpuhp_state, list);
> -    }
> +    acpi_cpu_ospm_status(&s->cpuhp_state, list);
>  }
>  
>  static void piix4_send_gpe(AcpiDeviceIf *adev, AcpiEventStatusBits ev)
> diff --git a/hw/i386/acpi-build.c b/hw/i386/acpi-build.c
> index 23147ddc25e7..bf7ed2e50837 100644
> --- a/hw/i386/acpi-build.c
> +++ b/hw/i386/acpi-build.c
> @@ -960,9 +960,7 @@ build_dsdt(GArray *table_data, BIOSLinker *linker,
>      }
>      aml_append(dsdt, scope);
>  
> -    if (pcmc->legacy_cpu_hotplug) {
> -        build_legacy_cpu_hotplug_aml(dsdt, machine, pm->cpu_hp_io_base);
> -    } else {
> +    {
>          CPUHotplugFeatures opts = {
>              .acpi_1_compatible = true,
>              .smi_path = pm->smi_on_cpuhp ? "\\_SB.PCI0.SMI0.SMIC" : NULL,
> diff --git a/include/hw/acpi/ich9.h b/include/hw/acpi/ich9.h
> index 245fe08dc245..6a21472eb32e 100644
> --- a/include/hw/acpi/ich9.h
> +++ b/include/hw/acpi/ich9.h
> @@ -53,8 +53,6 @@ typedef struct ICH9LPCPMRegs {
>      uint32_t pm_io_base;
>      Notifier powerdown_notifier;
>  
> -    bool cpu_hotplug_legacy;
> -    AcpiCpuHotplug gpe_cpu;
>      CPUHotplugState cpuhp_state;
>  
>      bool keep_pci_slot_hpc;
> diff --git a/include/hw/acpi/piix4.h b/include/hw/acpi/piix4.h
> index eb1c122d8069..e075f0cbeaf1 100644
> --- a/include/hw/acpi/piix4.h
> +++ b/include/hw/acpi/piix4.h
> @@ -63,8 +63,6 @@ struct PIIX4PMState {
>      uint8_t disable_s4;
>      uint8_t s4_val;
>  
> -    bool cpu_hotplug_legacy;
> -    AcpiCpuHotplug gpe_cpu;
>      CPUHotplugState cpuhp_state;
>  
>      MemHotplugState acpi_memory_hotplug;
> diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
> index e83157ab358f..698e3fb84af0 100644
> --- a/include/hw/i386/pc.h
> +++ b/include/hw/i386/pc.h
> @@ -110,9 +110,6 @@ struct PCMachineClass {
>      bool enforce_amd_1tb_hole;
>      bool isa_bios_alias;
>  
> -    /* generate legacy CPU hotplug AML */
> -    bool legacy_cpu_hotplug;
> -
>      /* use PVH to load kernels that support this feature */
>      bool pvh_enabled;
>