pc: use new CPU hotplug interface since 2.7 machine type

For compatibility reasons PC/Q35 will start with legacy
CPU hotplug interface by default but with new CPU hotplug
AML code since 2.7 machine type. That way legacy firmware
that doesn't use QEMU generated ACPI tables will be
able to continue using legacy CPU hotplug interface.

While new machine type, with firmware supporting QEMU
provided ACPI tables, will generate new CPU hotplug AML,
which will switch to new CPU hotplug interface when
guest OS executes its _INI method on ACPI tables
loading.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

4 files changed, 94 insertions, 1 deletions

diff --git a/hw/acpi/cpu.c b/hw/acpi/cpu.c
index 401ac0dab2..c13b65c2c9 100644
--- a/hw/acpi/cpu.c
+++ b/hw/acpi/cpu.c
@@ -373,6 +373,15 @@ void build_cpus_aml(Aml *table, MachineState *machine, CPUHotplugFeatures opts,
         aml_append(field, aml_named_field(CPU_DATA, 32));
         aml_append(cpu_ctrl_dev, field);
 
+        if (opts.has_legacy_cphp) {
+            method = aml_method("_INI", 0, AML_SERIALIZED);
+            /* switch off legacy CPU hotplug HW and use new one,
+             * on reboot system is in new mode and writing 0
+             * in CPU_SELECTOR selects BSP, which is NOP at
+             * the time _INI is called */
+            aml_append(method, aml_store(zero, aml_name(CPU_SELECTOR)));
+            aml_append(cpu_ctrl_dev, method);
+        }
     }
     aml_append(sb_scope, cpu_ctrl_dev);
 
diff --git a/hw/acpi/cpu_hotplug.c b/hw/acpi/cpu_hotplug.c
index fe75bd9ac9..e19d902063 100644
--- a/hw/acpi/cpu_hotplug.c
+++ b/hw/acpi/cpu_hotplug.c
@@ -34,7 +34,15 @@ static uint64_t cpu_status_read(void *opaque, hwaddr addr, unsigned int size)
 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 */
+    /* firmware never used to write in CPU present bitmap so use
+       this fact as means to switch QEMU into modern CPU hotplug
+       mode by writing 0 at the beginning of legacy CPU bitmap
+     */
+    if (addr == 0 && data == 0) {
+        AcpiCpuHotplug *cpus = opaque;
+        object_property_set_bool(cpus->device, false, "cpu-hotplug-legacy",
+                                 &error_abort);
+    }
 }
 
 static const MemoryRegionOps AcpiCpuHotplug_ops = {
@@ -83,6 +91,17 @@ void legacy_acpi_cpu_hotplug_init(MemoryRegion *parent, Object *owner,
     memory_region_init_io(&gpe_cpu->io, owner, &AcpiCpuHotplug_ops,
                           gpe_cpu, "acpi-cpu-hotplug", ACPI_GPE_PROC_LEN);
     memory_region_add_subregion(parent, base, &gpe_cpu->io);
+    gpe_cpu->device = owner;
+}
+
+void acpi_switch_to_modern_cphp(AcpiCpuHotplug *gpe_cpu,
+                                CPUHotplugState *cpuhp_state,
+                                uint16_t io_port)
+{
+    MemoryRegion *parent = pci_address_space_io(PCI_DEVICE(gpe_cpu->device));
+
+    memory_region_del_subregion(parent, &gpe_cpu->io);
+    cpu_hotplug_hw_init(parent, gpe_cpu->device, cpuhp_state, io_port);
 }
 
 void build_legacy_cpu_hotplug_aml(Aml *ctx, MachineState *machine,
diff --git a/hw/acpi/ich9.c b/hw/acpi/ich9.c
index d12cc62381..e5a3c18e52 100644
--- a/hw/acpi/ich9.c
+++ b/hw/acpi/ich9.c
@@ -189,6 +189,33 @@ static const VMStateDescription vmstate_tco_io_state = {
     }
 };
 
+static bool vmstate_test_use_cpuhp(void *opaque)
+{
+    ICH9LPCPMRegs *s = opaque;
+    return !s->cpu_hotplug_legacy;
+}
+
+static int vmstate_cpuhp_pre_load(void *opaque)
+{
+    ICH9LPCPMRegs *s = opaque;
+    Object *obj = OBJECT(s->gpe_cpu.device);
+    object_property_set_bool(obj, false, "cpu-hotplug-legacy", &error_abort);
+    return 0;
+}
+
+static const VMStateDescription vmstate_cpuhp_state = {
+    .name = "ich9_pm/cpuhp",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .needed = vmstate_test_use_cpuhp,
+    .pre_load = vmstate_cpuhp_pre_load,
+    .fields      = (VMStateField[]) {
+        VMSTATE_CPU_HOTPLUG(cpuhp_state, ICH9LPCPMRegs),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 const VMStateDescription vmstate_ich9_pm = {
     .name = "ich9_pm",
     .version_id = 1,
@@ -209,6 +236,7 @@ const VMStateDescription vmstate_ich9_pm = {
     .subsections = (const VMStateDescription*[]) {
         &vmstate_memhp_state,
         &vmstate_tco_io_state,
+        &vmstate_cpuhp_state,
         NULL
     }
 };
@@ -318,6 +346,11 @@ static void ich9_pm_set_cpu_hotplug_legacy(Object *obj, bool value,
 {
     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;
 }
 
diff --git a/hw/acpi/piix4.c b/hw/acpi/piix4.c
index 858244a661..2adc246b00 100644
--- a/hw/acpi/piix4.c
+++ b/hw/acpi/piix4.c
@@ -276,6 +276,32 @@ static const VMStateDescription vmstate_memhp_state = {
     }
 };
 
+static bool vmstate_test_use_cpuhp(void *opaque)
+{
+    PIIX4PMState *s = opaque;
+    return !s->cpu_hotplug_legacy;
+}
+
+static int vmstate_cpuhp_pre_load(void *opaque)
+{
+    Object *obj = OBJECT(opaque);
+    object_property_set_bool(obj, false, "cpu-hotplug-legacy", &error_abort);
+    return 0;
+}
+
+static const VMStateDescription vmstate_cpuhp_state = {
+    .name = "piix4_pm/cpuhp",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .minimum_version_id_old = 1,
+    .needed = vmstate_test_use_cpuhp,
+    .pre_load = vmstate_cpuhp_pre_load,
+    .fields      = (VMStateField[]) {
+        VMSTATE_CPU_HOTPLUG(cpuhp_state, PIIX4PMState),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 /* 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
@@ -310,6 +336,7 @@ static const VMStateDescription vmstate_acpi = {
     },
     .subsections = (const VMStateDescription*[]) {
          &vmstate_memhp_state,
+         &vmstate_cpuhp_state,
          NULL
     }
 };
@@ -585,6 +612,11 @@ 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;
 }