hw/i386: Move save_tsc_khz from PCMachineClass to X86MachineClass

Attempting to migrate a VM using the microvm machine class results in the source
QEMU aborting with the following message/backtrace:

target/i386/machine.c:955:tsc_khz_needed: Object 0x555556608fa0 is not an
instance of type generic-pc-machine

abort()
object_class_dynamic_cast_assert()
vmstate_save_state_v()
vmstate_save_state()
vmstate_save()
qemu_savevm_state_complete_precopy()
migration_thread()
migration_thread()
migration_thread()
qemu_thread_start()
start_thread()
clone()

The access to the machine class returned by MACHINE_GET_CLASS() in
tsc_khz_needed() is crashing as it is trying to dereference a different
type of machine class object (TYPE_PC_MACHINE) to that of this microVM.

This can be resolved by extending the changes in the following commit
f0bb276bf8d5 ("hw/i386: split PCMachineState deriving X86MachineState from it")
and moving the save_tsc_khz field in PCMachineClass to X86MachineClass.

Fixes: f0bb276bf8d5 ("hw/i386: split PCMachineState deriving X86MachineState from it")
Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Message-Id: <1574075605-25215-1-git-send-email-liam.merwick@oracle.com>
Reviewed-by: Sergio Lopez <slp@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

hw/i386/pc.c

@@ -2195,7 +2195,6 @@ static void pc_machine_class_init(ObjectClass *oc, void *data)
     /* BIOS ACPI tables: 128K. Other BIOS datastructures: less than 4K reported
      * to be used at the moment, 32K should be enough for a while.  */
     pcmc->acpi_data_size = 0x20000 + 0x8000;
-    pcmc->save_tsc_khz = true;
     pcmc->linuxboot_dma_enabled = true;
     pcmc->pvh_enabled = true;
     assert(!mc->get_hotplug_handler);

hw/i386/pc_piix.c

@@ -567,10 +567,10 @@ DEFINE_I440FX_MACHINE(v2_6, "pc-i440fx-2.6", NULL,
 
 static void pc_i440fx_2_5_machine_options(MachineClass *m)
 {
-    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+    X86MachineClass *x86mc = X86_MACHINE_CLASS(m);
 
     pc_i440fx_2_6_machine_options(m);
-    pcmc->save_tsc_khz = false;
+    x86mc->save_tsc_khz = false;
     m->legacy_fw_cfg_order = 1;
     compat_props_add(m->compat_props, hw_compat_2_5, hw_compat_2_5_len);
     compat_props_add(m->compat_props, pc_compat_2_5, pc_compat_2_5_len);

hw/i386/pc_q35.c

@@ -508,10 +508,10 @@ DEFINE_Q35_MACHINE(v2_6, "pc-q35-2.6", NULL,
 
 static void pc_q35_2_5_machine_options(MachineClass *m)
 {
-    PCMachineClass *pcmc = PC_MACHINE_CLASS(m);
+    X86MachineClass *x86mc = X86_MACHINE_CLASS(m);
 
     pc_q35_2_6_machine_options(m);
-    pcmc->save_tsc_khz = false;
+    x86mc->save_tsc_khz = false;
     m->legacy_fw_cfg_order = 1;
     compat_props_add(m->compat_props, hw_compat_2_5, hw_compat_2_5_len);
     compat_props_add(m->compat_props, pc_compat_2_5, pc_compat_2_5_len);

hw/i386/x86.c

@@ -763,6 +763,7 @@ static void x86_machine_class_init(ObjectClass *oc, void *data)
     mc->get_default_cpu_node_id = x86_get_default_cpu_node_id;
     mc->possible_cpu_arch_ids = x86_possible_cpu_arch_ids;
     x86mc->compat_apic_id_mode = false;
+    x86mc->save_tsc_khz = true;
     nc->nmi_monitor_handler = x86_nmi;
 
     object_class_property_add(oc, X86_MACHINE_MAX_RAM_BELOW_4G, "size",

include/hw/i386/pc.h

@@ -116,8 +116,6 @@ typedef struct PCMachineClass {
     bool enforce_aligned_dimm;
     bool broken_reserved_end;
 
-    /* TSC rate migration: */
-    bool save_tsc_khz;
     /* generate legacy CPU hotplug AML */
     bool legacy_cpu_hotplug;
 

include/hw/i386/x86.h

@@ -30,6 +30,8 @@ typedef struct {
 
     /*< public >*/
 
+    /* TSC rate migration: */
+    bool save_tsc_khz;
     /* Enables contiguous-apic-ID mode */
     bool compat_apic_id_mode;
 } X86MachineClass;

target/i386/machine.c

@@ -988,8 +988,8 @@ static bool tsc_khz_needed(void *opaque)
     X86CPU *cpu = opaque;
     CPUX86State *env = &cpu->env;
     MachineClass *mc = MACHINE_GET_CLASS(qdev_get_machine());
-    PCMachineClass *pcmc = PC_MACHINE_CLASS(mc);
-    return env->tsc_khz && pcmc->save_tsc_khz;
+    X86MachineClass *x86mc = X86_MACHINE_CLASS(mc);
+    return env->tsc_khz && x86mc->save_tsc_khz;
 }
 
 static const VMStateDescription vmstate_tsc_khz = {