Patchwork [13/22] acpi_piix4: add infrastructure to send CPU hot-plug GPE to guest

login
register
mail settings
Submitter Igor Mammedov
Date April 5, 2013, 2:37 p.m.
Message ID <1365172636-28628-14-git-send-email-imammedo@redhat.com>
Download mbox | patch
Permalink /patch/234172/
State New
Headers show

Comments

Igor Mammedov - April 5, 2013, 2:37 p.m.
* introduce processor status bitmask visible to guest at 0xaf00 addr,
  where Seabios expects it
* set bit corresponding to APIC ID in processor status bitmask on
  receiving CPU hot-plug notification
* trigger CPU hot-plug SCI, expected by Seabios on receiving CPU
  hot-plug notification

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
---
v2:
  * use CPUClass.get_firmware_id() to make code target independent
  * bump up vmstate_acpi version
---
 hw/acpi_piix4.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 111 insertions(+), 3 deletions(-)
liguang - April 8, 2013, 2:24 a.m.
在 2013-04-05五的 16:37 +0200,Igor Mammedov写道:
> * introduce processor status bitmask visible to guest at 0xaf00 addr,
>   where Seabios expects it
> * set bit corresponding to APIC ID in processor status bitmask on
>   receiving CPU hot-plug notification
> * trigger CPU hot-plug SCI, expected by Seabios on receiving CPU
>   hot-plug notification

expected by seabios?
IMHO, seems you are saying ACPI's asl code which
just wrapped in seabios.

> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> v2:
>   * use CPUClass.get_firmware_id() to make code target independent
>   * bump up vmstate_acpi version
> ---
>  hw/acpi_piix4.c | 114 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 111 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
> index 48a32b5..ccfc028 100644
> --- a/hw/acpi_piix4.c
> +++ b/hw/acpi_piix4.c
> @@ -48,19 +48,28 @@
>  #define PCI_EJ_BASE 0xae08
>  #define PCI_RMV_BASE 0xae0c
>  
> +#define PROC_BASE 0xaf00
> +#define PROC_LEN 32
> +
>  #define PIIX4_PCI_HOTPLUG_STATUS 2
> +#define PIIX4_CPU_HOTPLUG_STATUS 4
>  
>  struct pci_status {
>      uint32_t up; /* deprecated, maintained for migration compatibility */
>      uint32_t down;
>  };
>  
> +struct cpu_status {
> +    uint8_t sts[PROC_LEN];
> +};
> +
>  typedef struct PIIX4PMState {
>      PCIDevice dev;
>  
>      MemoryRegion io;
>      MemoryRegion io_gpe;
>      MemoryRegion io_pci;
> +    MemoryRegion io_cpu;
>      ACPIREGS ar;
>  
>      APMState apm;
> @@ -82,6 +91,9 @@ typedef struct PIIX4PMState {
>      uint8_t disable_s3;
>      uint8_t disable_s4;
>      uint8_t s4_val;
> +
> +    struct cpu_status gpe_cpu;
> +    Notifier cpu_add_notifier;

seems you named cpu_added_notifier at [PATCH 10/22],
should the notifer's name be unified?

>  } PIIX4PMState;
>  
>  static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
> @@ -100,8 +112,8 @@ static void pm_update_sci(PIIX4PMState *s)
>                     ACPI_BITMASK_POWER_BUTTON_ENABLE |
>                     ACPI_BITMASK_GLOBAL_LOCK_ENABLE |
>                     ACPI_BITMASK_TIMER_ENABLE)) != 0) ||
> -        (((s->ar.gpe.sts[0] & s->ar.gpe.en[0])
> -          & PIIX4_PCI_HOTPLUG_STATUS) != 0);
> +        (((s->ar.gpe.sts[0] & s->ar.gpe.en[0]) &
> +          (PIIX4_PCI_HOTPLUG_STATUS | PIIX4_CPU_HOTPLUG_STATUS)) != 0);
>  
>      qemu_set_irq(s->irq, sci_level);
>      /* schedule a timer interruption if needed */
> @@ -257,6 +269,17 @@ static int acpi_load_old(QEMUFile *f, void *opaque, int version_id)
>      return ret;
>  }
>  
> +#define VMSTATE_CPU_STATUS_ARRAY(_field, _state)                             \
> + {                                                                           \
> +     .name       = (stringify(_field)),                                      \
> +     .version_id = 0,                                                        \
> +     .num        = PROC_LEN,                                                 \
> +     .info       = &vmstate_info_uint8,                                      \
> +     .size       = sizeof(uint8_t),                                          \
> +     .flags      = VMS_ARRAY,                                                \
> +     .offset     = vmstate_offset_array(_state, _field, uint8_t, PROC_LEN),  \
> + }
> +
>  /* qemu-kvm 1.2 uses version 3 but advertised as 2
>   * To support incoming qemu-kvm 1.2 migration, change version_id
>   * and minimum_version_id to 2 below (which breaks migration from
> @@ -265,7 +288,7 @@ static int acpi_load_old(QEMUFile *f, void *opaque, int version_id)
>   */
>  static const VMStateDescription vmstate_acpi = {
>      .name = "piix4_pm",
> -    .version_id = 3,
> +    .version_id = 4,
>      .minimum_version_id = 3,
>      .minimum_version_id_old = 1,
>      .load_state_old = acpi_load_old,
> @@ -281,6 +304,7 @@ static const VMStateDescription vmstate_acpi = {
>          VMSTATE_STRUCT(ar.gpe, PIIX4PMState, 2, vmstate_gpe, ACPIGPE),
>          VMSTATE_STRUCT(pci0_status, PIIX4PMState, 2, vmstate_pci_status,
>                         struct pci_status),
> +        VMSTATE_CPU_STATUS_ARRAY(gpe_cpu.sts, PIIX4PMState),
>          VMSTATE_END_OF_LIST()
>      }
>  };
> @@ -585,6 +609,83 @@ static const MemoryRegionOps piix4_pci_ops = {
>      },
>  };
>  
> +static uint64_t cpu_status_read(void *opaque, hwaddr addr, unsigned width)
> +{
> +    PIIX4PMState *s = opaque;
> +    struct cpu_status *cpus = &s->gpe_cpu;
> +    uint64_t val = cpus->sts[addr];
> +    return val;
> +}
> +
> +static void cpu_status_write(void *opaque, hwaddr addr, uint64_t data,
> +                             unsigned int size)
> +{
> +    /* TODO: implement VCPU removal on guest signal that CPU can be removed */
> +}
> +
> +static const MemoryRegionOps cpu_hotplug_ops = {
> +    .read = cpu_status_read,
> +    .write = cpu_status_write,
> +    .endianness = DEVICE_LITTLE_ENDIAN,
> +    .valid = {
> +        .min_access_size = 1,
> +        .max_access_size = 1,
> +    },
> +};
> +
> +typedef enum {
> +    PLUG,
> +    UNPLUG,
> +} HotplugEventType;
> +
> +static void piix4_cpu_hotplug_req(PIIX4PMState *s, CPUState *cpu,
> +                                  HotplugEventType action)
> +{
> +    struct cpu_status *g = &s->gpe_cpu;
> +    ACPIGPE *gpe = &s->ar.gpe;
> +    CPUClass *k = CPU_GET_CLASS(cpu);
> +    int64_t cpu_id;
> +
> +    assert(s != NULL);
> +
> +    *gpe->sts = *gpe->sts | PIIX4_CPU_HOTPLUG_STATUS;
> +    cpu_id = k->get_firmware_id(CPU(cpu));
> +    if (action == PLUG) {
> +        g->sts[cpu_id / 8] |= (1 << (cpu_id % 8));
> +    } else {
> +        g->sts[cpu_id / 8] &= ~(1 << (cpu_id % 8));
> +    }
> +    pm_update_sci(s);
> +}
> +
> +static void piix4_cpu_add_req(Notifier *n, void *opaque)
> +{
> +    PIIX4PMState *s = container_of(n, PIIX4PMState, cpu_add_notifier);
> +    piix4_cpu_hotplug_req(s, CPU(opaque), PLUG);
> +}
> +
> +static int piix4_init_cpu_status(Object *obj, void *opaque)
> +{
> +    struct cpu_status *g = (struct cpu_status *)opaque;
> +    Object *cpu_obj = object_dynamic_cast(obj, TYPE_CPU);
> +
> +    if (cpu_obj) {
> +        struct Error *error = NULL;
> +        CPUClass *k = CPU_GET_CLASS(cpu_obj);
> +        int64_t id = k->get_firmware_id(CPU(cpu_obj));
> +
> +        if (error) {
> +            fprintf(stderr, "failed to initilize CPU status for ACPI: %s\n",
> +                    error_get_pretty(error));
> +            error_free(error);
> +            abort();
> +        }
> +        g_assert((id / 8) < PROC_LEN);
> +        g->sts[id / 8] |= (1 << (id % 8));
> +    }
> +    return object_child_foreach(obj, piix4_init_cpu_status, opaque);
> +}
> +
>  static int piix4_device_hotplug(DeviceState *qdev, PCIDevice *dev,
>                                  PCIHotplugState state);
>  
> @@ -600,6 +701,13 @@ static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
>      memory_region_add_subregion(parent, PCI_HOTPLUG_ADDR,
>                                  &s->io_pci);
>      pci_bus_hotplug(bus, piix4_device_hotplug, &s->dev.qdev);
> +
> +    piix4_init_cpu_status(qdev_get_machine(), &s->gpe_cpu);
> +    memory_region_init_io(&s->io_cpu, &cpu_hotplug_ops, s, "apci-cpu-hotplug",
> +                          PROC_LEN);
> +    memory_region_add_subregion(parent, PROC_BASE, &s->io_cpu);
> +    s->cpu_add_notifier.notify = piix4_cpu_add_req;
> +    qemu_register_cpu_added_notifier(&s->cpu_add_notifier);
>  }
>  
>  static void enable_device(PIIX4PMState *s, int slot)
Igor Mammedov - April 8, 2013, 11:47 a.m.
On Mon, 08 Apr 2013 10:24:50 +0800
li guang <lig.fnst@cn.fujitsu.com> wrote:

> 在 2013-04-05五的 16:37 +0200,Igor Mammedov写道:
> > * introduce processor status bitmask visible to guest at 0xaf00 addr,
> >   where Seabios expects it
> > * set bit corresponding to APIC ID in processor status bitmask on
> >   receiving CPU hot-plug notification
> > * trigger CPU hot-plug SCI, expected by Seabios on receiving CPU
> >   hot-plug notification
> 
> expected by seabios?
> IMHO, seems you are saying ACPI's asl code which
> just wrapped in seabios.
Yep, that's what ACPI asl code there expects. With current effort to move
ACPI tables into it might be better to s/Seabios/ACPI/ here.

> > 
> > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > ---
> > v2:
> >   * use CPUClass.get_firmware_id() to make code target independent
> >   * bump up vmstate_acpi version
> > ---
> >  hw/acpi_piix4.c | 114
> > ++++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed,
> > 111 insertions(+), 3 deletions(-)
> > 
> > diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
> > index 48a32b5..ccfc028 100644
> > --- a/hw/acpi_piix4.c
> > +++ b/hw/acpi_piix4.c
> > @@ -48,19 +48,28 @@
> >  #define PCI_EJ_BASE 0xae08
> >  #define PCI_RMV_BASE 0xae0c
> >  
> > +#define PROC_BASE 0xaf00
> > +#define PROC_LEN 32
> > +
> >  #define PIIX4_PCI_HOTPLUG_STATUS 2
> > +#define PIIX4_CPU_HOTPLUG_STATUS 4
> >  
> >  struct pci_status {
> >      uint32_t up; /* deprecated, maintained for migration compatibility */
> >      uint32_t down;
> >  };
> >  
> > +struct cpu_status {
> > +    uint8_t sts[PROC_LEN];
> > +};
> > +
> >  typedef struct PIIX4PMState {
> >      PCIDevice dev;
> >  
> >      MemoryRegion io;
> >      MemoryRegion io_gpe;
> >      MemoryRegion io_pci;
> > +    MemoryRegion io_cpu;
> >      ACPIREGS ar;
> >  
> >      APMState apm;
> > @@ -82,6 +91,9 @@ typedef struct PIIX4PMState {
> >      uint8_t disable_s3;
> >      uint8_t disable_s4;
> >      uint8_t s4_val;
> > +
> > +    struct cpu_status gpe_cpu;
> > +    Notifier cpu_add_notifier;
> 
> seems you named cpu_added_notifier at [PATCH 10/22],
> should the notifer's name be unified?
I'll fix it on next respin, thanks.

> 
> >  } PIIX4PMState;
> >  
> >  static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
> > @@ -100,8 +112,8 @@ static void pm_update_sci(PIIX4PMState *s)
> >                     ACPI_BITMASK_POWER_BUTTON_ENABLE |
> >                     ACPI_BITMASK_GLOBAL_LOCK_ENABLE |
> >                     ACPI_BITMASK_TIMER_ENABLE)) != 0) ||
> > -        (((s->ar.gpe.sts[0] & s->ar.gpe.en[0])
> > -          & PIIX4_PCI_HOTPLUG_STATUS) != 0);
> > +        (((s->ar.gpe.sts[0] & s->ar.gpe.en[0]) &
> > +          (PIIX4_PCI_HOTPLUG_STATUS | PIIX4_CPU_HOTPLUG_STATUS)) != 0);
> >  
> >      qemu_set_irq(s->irq, sci_level);
> >      /* schedule a timer interruption if needed */
> > @@ -257,6 +269,17 @@ static int acpi_load_old(QEMUFile *f, void *opaque,
> > int version_id) return ret;
> >  }
> >  
> > +#define VMSTATE_CPU_STATUS_ARRAY(_field,
> > _state)                             \
> > +
> > {                                                                           \
> > +     .name       =
> > (stringify(_field)),                                      \
> > +     .version_id =
> > 0,                                                        \
> > +     .num        =
> > PROC_LEN,                                                 \
> > +     .info       =
> > &vmstate_info_uint8,                                      \
> > +     .size       =
> > sizeof(uint8_t),                                          \
> > +     .flags      =
> > VMS_ARRAY,                                                \
> > +     .offset     = vmstate_offset_array(_state, _field, uint8_t,
> > PROC_LEN),  \
> > + }
> > +
> >  /* qemu-kvm 1.2 uses version 3 but advertised as 2
> >   * To support incoming qemu-kvm 1.2 migration, change version_id
> >   * and minimum_version_id to 2 below (which breaks migration from
> > @@ -265,7 +288,7 @@ static int acpi_load_old(QEMUFile *f, void *opaque,
> > int version_id) */
> >  static const VMStateDescription vmstate_acpi = {
> >      .name = "piix4_pm",
> > -    .version_id = 3,
> > +    .version_id = 4,
> >      .minimum_version_id = 3,
> >      .minimum_version_id_old = 1,
> >      .load_state_old = acpi_load_old,
> > @@ -281,6 +304,7 @@ static const VMStateDescription vmstate_acpi = {
> >          VMSTATE_STRUCT(ar.gpe, PIIX4PMState, 2, vmstate_gpe, ACPIGPE),
> >          VMSTATE_STRUCT(pci0_status, PIIX4PMState, 2, vmstate_pci_status,
> >                         struct pci_status),
> > +        VMSTATE_CPU_STATUS_ARRAY(gpe_cpu.sts, PIIX4PMState),
> >          VMSTATE_END_OF_LIST()
> >      }
> >  };
> > @@ -585,6 +609,83 @@ static const MemoryRegionOps piix4_pci_ops = {
> >      },
> >  };
> >  
> > +static uint64_t cpu_status_read(void *opaque, hwaddr addr, unsigned
> > width) +{
> > +    PIIX4PMState *s = opaque;
> > +    struct cpu_status *cpus = &s->gpe_cpu;
> > +    uint64_t val = cpus->sts[addr];
> > +    return val;
> > +}
> > +
> > +static void cpu_status_write(void *opaque, hwaddr addr, uint64_t data,
> > +                             unsigned int size)
> > +{
> > +    /* TODO: implement VCPU removal on guest signal that CPU can be
> > removed */ +}
> > +
> > +static const MemoryRegionOps cpu_hotplug_ops = {
> > +    .read = cpu_status_read,
> > +    .write = cpu_status_write,
> > +    .endianness = DEVICE_LITTLE_ENDIAN,
> > +    .valid = {
> > +        .min_access_size = 1,
> > +        .max_access_size = 1,
> > +    },
> > +};
> > +
> > +typedef enum {
> > +    PLUG,
> > +    UNPLUG,
> > +} HotplugEventType;
> > +
> > +static void piix4_cpu_hotplug_req(PIIX4PMState *s, CPUState *cpu,
> > +                                  HotplugEventType action)
> > +{
> > +    struct cpu_status *g = &s->gpe_cpu;
> > +    ACPIGPE *gpe = &s->ar.gpe;
> > +    CPUClass *k = CPU_GET_CLASS(cpu);
> > +    int64_t cpu_id;
> > +
> > +    assert(s != NULL);
> > +
> > +    *gpe->sts = *gpe->sts | PIIX4_CPU_HOTPLUG_STATUS;
> > +    cpu_id = k->get_firmware_id(CPU(cpu));
> > +    if (action == PLUG) {
> > +        g->sts[cpu_id / 8] |= (1 << (cpu_id % 8));
> > +    } else {
> > +        g->sts[cpu_id / 8] &= ~(1 << (cpu_id % 8));
> > +    }
> > +    pm_update_sci(s);
> > +}
> > +
> > +static void piix4_cpu_add_req(Notifier *n, void *opaque)
> > +{
> > +    PIIX4PMState *s = container_of(n, PIIX4PMState, cpu_add_notifier);
> > +    piix4_cpu_hotplug_req(s, CPU(opaque), PLUG);
> > +}
> > +
> > +static int piix4_init_cpu_status(Object *obj, void *opaque)
> > +{
> > +    struct cpu_status *g = (struct cpu_status *)opaque;
> > +    Object *cpu_obj = object_dynamic_cast(obj, TYPE_CPU);
> > +
> > +    if (cpu_obj) {
> > +        struct Error *error = NULL;
> > +        CPUClass *k = CPU_GET_CLASS(cpu_obj);
> > +        int64_t id = k->get_firmware_id(CPU(cpu_obj));
> > +
> > +        if (error) {
> > +            fprintf(stderr, "failed to initilize CPU status for ACPI:
> > %s\n",
> > +                    error_get_pretty(error));
> > +            error_free(error);
> > +            abort();
> > +        }
> > +        g_assert((id / 8) < PROC_LEN);
> > +        g->sts[id / 8] |= (1 << (id % 8));
> > +    }
> > +    return object_child_foreach(obj, piix4_init_cpu_status, opaque);
> > +}
> > +
> >  static int piix4_device_hotplug(DeviceState *qdev, PCIDevice *dev,
> >                                  PCIHotplugState state);
> >  
> > @@ -600,6 +701,13 @@ static void
> > piix4_acpi_system_hot_add_init(MemoryRegion *parent,
> > memory_region_add_subregion(parent, PCI_HOTPLUG_ADDR, &s->io_pci);
> >      pci_bus_hotplug(bus, piix4_device_hotplug, &s->dev.qdev);
> > +
> > +    piix4_init_cpu_status(qdev_get_machine(), &s->gpe_cpu);
> > +    memory_region_init_io(&s->io_cpu, &cpu_hotplug_ops, s,
> > "apci-cpu-hotplug",
> > +                          PROC_LEN);
> > +    memory_region_add_subregion(parent, PROC_BASE, &s->io_cpu);
> > +    s->cpu_add_notifier.notify = piix4_cpu_add_req;
> > +    qemu_register_cpu_added_notifier(&s->cpu_add_notifier);
> >  }
> >  
> >  static void enable_device(PIIX4PMState *s, int slot)
> 
>

Patch

diff --git a/hw/acpi_piix4.c b/hw/acpi_piix4.c
index 48a32b5..ccfc028 100644
--- a/hw/acpi_piix4.c
+++ b/hw/acpi_piix4.c
@@ -48,19 +48,28 @@ 
 #define PCI_EJ_BASE 0xae08
 #define PCI_RMV_BASE 0xae0c
 
+#define PROC_BASE 0xaf00
+#define PROC_LEN 32
+
 #define PIIX4_PCI_HOTPLUG_STATUS 2
+#define PIIX4_CPU_HOTPLUG_STATUS 4
 
 struct pci_status {
     uint32_t up; /* deprecated, maintained for migration compatibility */
     uint32_t down;
 };
 
+struct cpu_status {
+    uint8_t sts[PROC_LEN];
+};
+
 typedef struct PIIX4PMState {
     PCIDevice dev;
 
     MemoryRegion io;
     MemoryRegion io_gpe;
     MemoryRegion io_pci;
+    MemoryRegion io_cpu;
     ACPIREGS ar;
 
     APMState apm;
@@ -82,6 +91,9 @@  typedef struct PIIX4PMState {
     uint8_t disable_s3;
     uint8_t disable_s4;
     uint8_t s4_val;
+
+    struct cpu_status gpe_cpu;
+    Notifier cpu_add_notifier;
 } PIIX4PMState;
 
 static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
@@ -100,8 +112,8 @@  static void pm_update_sci(PIIX4PMState *s)
                    ACPI_BITMASK_POWER_BUTTON_ENABLE |
                    ACPI_BITMASK_GLOBAL_LOCK_ENABLE |
                    ACPI_BITMASK_TIMER_ENABLE)) != 0) ||
-        (((s->ar.gpe.sts[0] & s->ar.gpe.en[0])
-          & PIIX4_PCI_HOTPLUG_STATUS) != 0);
+        (((s->ar.gpe.sts[0] & s->ar.gpe.en[0]) &
+          (PIIX4_PCI_HOTPLUG_STATUS | PIIX4_CPU_HOTPLUG_STATUS)) != 0);
 
     qemu_set_irq(s->irq, sci_level);
     /* schedule a timer interruption if needed */
@@ -257,6 +269,17 @@  static int acpi_load_old(QEMUFile *f, void *opaque, int version_id)
     return ret;
 }
 
+#define VMSTATE_CPU_STATUS_ARRAY(_field, _state)                             \
+ {                                                                           \
+     .name       = (stringify(_field)),                                      \
+     .version_id = 0,                                                        \
+     .num        = PROC_LEN,                                                 \
+     .info       = &vmstate_info_uint8,                                      \
+     .size       = sizeof(uint8_t),                                          \
+     .flags      = VMS_ARRAY,                                                \
+     .offset     = vmstate_offset_array(_state, _field, uint8_t, PROC_LEN),  \
+ }
+
 /* qemu-kvm 1.2 uses version 3 but advertised as 2
  * To support incoming qemu-kvm 1.2 migration, change version_id
  * and minimum_version_id to 2 below (which breaks migration from
@@ -265,7 +288,7 @@  static int acpi_load_old(QEMUFile *f, void *opaque, int version_id)
  */
 static const VMStateDescription vmstate_acpi = {
     .name = "piix4_pm",
-    .version_id = 3,
+    .version_id = 4,
     .minimum_version_id = 3,
     .minimum_version_id_old = 1,
     .load_state_old = acpi_load_old,
@@ -281,6 +304,7 @@  static const VMStateDescription vmstate_acpi = {
         VMSTATE_STRUCT(ar.gpe, PIIX4PMState, 2, vmstate_gpe, ACPIGPE),
         VMSTATE_STRUCT(pci0_status, PIIX4PMState, 2, vmstate_pci_status,
                        struct pci_status),
+        VMSTATE_CPU_STATUS_ARRAY(gpe_cpu.sts, PIIX4PMState),
         VMSTATE_END_OF_LIST()
     }
 };
@@ -585,6 +609,83 @@  static const MemoryRegionOps piix4_pci_ops = {
     },
 };
 
+static uint64_t cpu_status_read(void *opaque, hwaddr addr, unsigned width)
+{
+    PIIX4PMState *s = opaque;
+    struct cpu_status *cpus = &s->gpe_cpu;
+    uint64_t val = cpus->sts[addr];
+    return val;
+}
+
+static void cpu_status_write(void *opaque, hwaddr addr, uint64_t data,
+                             unsigned int size)
+{
+    /* TODO: implement VCPU removal on guest signal that CPU can be removed */
+}
+
+static const MemoryRegionOps cpu_hotplug_ops = {
+    .read = cpu_status_read,
+    .write = cpu_status_write,
+    .endianness = DEVICE_LITTLE_ENDIAN,
+    .valid = {
+        .min_access_size = 1,
+        .max_access_size = 1,
+    },
+};
+
+typedef enum {
+    PLUG,
+    UNPLUG,
+} HotplugEventType;
+
+static void piix4_cpu_hotplug_req(PIIX4PMState *s, CPUState *cpu,
+                                  HotplugEventType action)
+{
+    struct cpu_status *g = &s->gpe_cpu;
+    ACPIGPE *gpe = &s->ar.gpe;
+    CPUClass *k = CPU_GET_CLASS(cpu);
+    int64_t cpu_id;
+
+    assert(s != NULL);
+
+    *gpe->sts = *gpe->sts | PIIX4_CPU_HOTPLUG_STATUS;
+    cpu_id = k->get_firmware_id(CPU(cpu));
+    if (action == PLUG) {
+        g->sts[cpu_id / 8] |= (1 << (cpu_id % 8));
+    } else {
+        g->sts[cpu_id / 8] &= ~(1 << (cpu_id % 8));
+    }
+    pm_update_sci(s);
+}
+
+static void piix4_cpu_add_req(Notifier *n, void *opaque)
+{
+    PIIX4PMState *s = container_of(n, PIIX4PMState, cpu_add_notifier);
+    piix4_cpu_hotplug_req(s, CPU(opaque), PLUG);
+}
+
+static int piix4_init_cpu_status(Object *obj, void *opaque)
+{
+    struct cpu_status *g = (struct cpu_status *)opaque;
+    Object *cpu_obj = object_dynamic_cast(obj, TYPE_CPU);
+
+    if (cpu_obj) {
+        struct Error *error = NULL;
+        CPUClass *k = CPU_GET_CLASS(cpu_obj);
+        int64_t id = k->get_firmware_id(CPU(cpu_obj));
+
+        if (error) {
+            fprintf(stderr, "failed to initilize CPU status for ACPI: %s\n",
+                    error_get_pretty(error));
+            error_free(error);
+            abort();
+        }
+        g_assert((id / 8) < PROC_LEN);
+        g->sts[id / 8] |= (1 << (id % 8));
+    }
+    return object_child_foreach(obj, piix4_init_cpu_status, opaque);
+}
+
 static int piix4_device_hotplug(DeviceState *qdev, PCIDevice *dev,
                                 PCIHotplugState state);
 
@@ -600,6 +701,13 @@  static void piix4_acpi_system_hot_add_init(MemoryRegion *parent,
     memory_region_add_subregion(parent, PCI_HOTPLUG_ADDR,
                                 &s->io_pci);
     pci_bus_hotplug(bus, piix4_device_hotplug, &s->dev.qdev);
+
+    piix4_init_cpu_status(qdev_get_machine(), &s->gpe_cpu);
+    memory_region_init_io(&s->io_cpu, &cpu_hotplug_ops, s, "apci-cpu-hotplug",
+                          PROC_LEN);
+    memory_region_add_subregion(parent, PROC_BASE, &s->io_cpu);
+    s->cpu_add_notifier.notify = piix4_cpu_add_req;
+    qemu_register_cpu_added_notifier(&s->cpu_add_notifier);
 }
 
 static void enable_device(PIIX4PMState *s, int slot)