1.主線程初始化

• qemu層kvm初始化類

//KVM初始化的入口的類
static const TypeInfo kvm_accel_type = {
    .name = TYPE_KVM_ACCEL,
    .parent = TYPE_ACCEL,
    .instance_init = kvm_accel_instance_init,
    .class_init = kvm_accel_class_init,
    .instance_size = sizeof(KVMState),
};
說明：
1.QOM模型，先執行class_init初始化函數，類似C++中構造函數，在new對象的時候調用
2.QOM模型，instance_finalize實例化函數，本類的具體實現

• 主線程kvm初始化

|-qemu_init
	|-module_call_init(MODULE_INIT_QOM); //vl.c
		|-kvm_type_init                //初始化注冊kvm類類型
	|-configure_accelerators           //vl.c
		|-do_configure_accelerator     //設置為kvm加速，比如有hax、hvf、tcg、kvm、xen、whpx不同加速等
		|-accel_init_machine
			|-acc->init_machine(ms);   //調用kvm_init接口，這個是kvm真正初始化的入口
				|-kvm_init             //kvm-all.c
	|-machine_run_board_init           //主板初始化，此時運行狀態即將設置為running或者prelaunch
		|-machine_class->init
			|-pc_init1                 //i386/pc_piix.c 進行CPU、Memory、VGA、NIC、PCI等的初始化
				|-x86_cpus_init        //x86的CPU初始化---cpu虛擬化
				|-pc_guest_info_init   //guest信息初始化
				|-smbios_set_defaults  //bios設置
				|-pc_memory_init       //分配內存和加載rom和bios --內存虛擬化
				|-pc_gsi_create        //中斷控制器
				|-i440fx_init          //初始化pci總線
				|-piix3_create         //初始化isa總線
				|-pc_i8259_create      //中斷控制器初始化
				|-pc_vga_init          //顯卡初始化
				|-pc_basic_device_init //基本硬件初始化
				|-pc_nic_init          //網卡初始化
				|-pci_create_simple    //創建pci主橋
關注的兩個熱點：
1.x86_cpus_init        //cpu虛擬化
2.pc_memory_init       //內存虛擬化

• 調用堆棧

(gdb) bt
 #0  pc_init1 (machine=0x555556e39800, pci_type=0x555556164c06 "i440FX", host_type=0x555556163b61 "i440FX-pcihost") at /home/cloud/qemu/qemu-5.0.0/hw/i386/pc_piix.c:74
 #1  0x0000555555a4362b in machine_run_board_init (machine=0x555556e39800) at hw/core/machine.c:1140
 #2  0x00005555559749ca in qemu_init (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at /home/cloud/qemu/qemu-5.0.0/softmmu/vl.c:4897
 #3  0x000055555585cd19 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at /home/cloud/qemu/qemu-5.0.0/softmmu/main.c:48

2.Qemu層vcpu初始化

• x86_vcpu初始化類

static const TypeInfo x86_cpu_type_info = {
    .name = TYPE_X86_CPU,
    .parent = TYPE_CPU,
    .instance_size = sizeof(X86CPU),
    .instance_init = x86_cpu_initfn,
    .abstract = true,
    .class_size = sizeof(X86CPUClass),
    .class_init = x86_cpu_common_class_init,
};
x86_cpu類型注冊：
|-type_init                                       //初始化的時候注冊，main函數運行前
	|-x86_cpu_register_types
		|-x86_cpu_type_info                       //class_init類似構造函數
			|-x86_cpu_common_class_init
				|-device_class_set_parent_realize //設置cpu初始化函數realize=x86_cpu_realizefn
					|-qemu_init_vcpu              //開始初始化vcpu

• vcpu初始化邏輯

|-x86_cpus_init
	|-x86_cpu_new                           //CPUState *cs = CPU(dev);
		|-object_new
			|-object_new_with_type
				|-type_initialize
				|-object_initialize_with_type
					|-type_initialize
						|-class_init        //調用x86_cpu_type_info的x86_cpu_common_class_init初始化x86_cpu
		|-object_property_set_bool
			|-object_property_set_qobject
				|-property_set_bool
					|-device_set_realized
						|-x86_cpu_realizefn   //vcpu初始化的實現，先初始化struct X86CPU再初始化struct CPUState 
							|-qemu_init_vcpu  //struct CPUState
								|-qemu_kvm_start_vcpu
									|-qemu_kvm_cpu_thread_fn
										|-kvm_init_vcpu
											|-kvm_get_vcpu        //通知kvm創建一個vcpu，返回一個kvm_fd
											|-kvm_ioctl           //從kvm獲取映射mmap_size
											|-mmap                //對kvm_fd進行以一個mmap_size大小映射
											|-kvm_arch_init_vcpu  //前面vcpu創建成功之后現在來真正的初始化
												|-kvm_arch_set_tsc_khz      //時鐘設置
												|-kvm_vcpu_ioctl            //KVM_GET_TSC_KHZ時鐘可以用戶設置和從kvm獲取，這里從KVM獲取再保存下來
												|-hyperv_handle_properties  //設置cpuids
												|-cpu_x86_cpuid             //獲取所有的CPUID信息，填充結構體，設置到寄存器中
												|-kvm_vcpu_ioctl            //前面構造KVM需要的cpuid_data數據，再通過KVM_SET_CPUID2給kvm設置cpuid
												|-kvm_init_msrs             //通知kvm設置msr寄存器
												|-hyperv_init_vcpu          //Hyper-V初始化vcpu保存一些信息在后續遷移時候恢復使用
										|-kvm_init_cpu_signals
										|-kvm_cpu_exec //每個vcpu對應一個線程，該線程循環執行

x86_cpu類繼承關系：子類->父類
struct X86CPU      -> struct CPUState -> struct DeviceState
struct X86CPUClass -> struct CPUClass
struct CPUX86State -> (struct X86CPU env)
DeviceClass 可以通過DeviceState獲取得到DEVICE_GET_CLASS(dev)。
說明：
1.這里x86_cpu_new調用比較抽象，涉及QOM
2.這里cpu虛擬的具體流程還要結合kvm的實現才能分析透徹
3.先初始化父類再初始化子類，先初始化Class，再初始化Device,再初始化State如先初始化x86CPU數據結構，再去針對CPUState進行初始化，CPUState初始化結合KVM完成。CPUState記錄的是和kvm交互的狀態信息，CPUX86State記錄的是一些寄存器、cpu狀態之類信息。

• 調用堆棧

(gdb) bt
 #0  x86_cpu_realizefn (dev=0x5555572bb6c0, errp=0x7fffffffca30) at /home/cloud/qemu/qemu-5.0.0/target/i386/cpu.c:6528
 #1  0x0000555555a3ab11 in device_set_realized (obj=<optimized out>, value=<optimized out>, errp=0x7fffffffcb20) at hw/core/qdev.c:891
 #2  0x0000555555bd744e in property_set_bool (obj=0x5555572bb6c0, v=<optimized out>, name=<optimized out>, opaque=0x555556c71020, errp=0x7fffffffcb20) at qom/object.c:2243
 #3  0x0000555555bdc10f in object_property_set_qobject (obj=obj@entry=0x5555572bb6c0, value=value@entry=0x5555572d68d0, name=name@entry=0x55555619ea48 "realized", errp=errp@entry=0x7fffffffcb20) at qom/qom-qobject.c:26
 #4  0x0000555555bd98d5 in object_property_set_bool (obj=0x5555572bb6c0, value=<optimized out>, name=0x55555619ea48 "realized", errp=0x7fffffffcb20) at qom/object.c:1395
 #5  0x0000555555944ebf in x86_cpu_new (x86ms=x86ms@entry=0x555556e39850, apic_id=0, errp=0x555556b7e6b0 <error_fatal>) at /home/cloud/qemu/qemu-5.0.0/hw/i386/x86.c:129
 #6  0x0000555555944ff9 in x86_cpus_init (x86ms=0x555556e39850, default_cpu_version=<optimized out>) at /home/cloud/qemu/qemu-5.0.0/hw/i386/x86.c:168
 #7  0x000055555594c2b9 in pc_init1 (machine=0x555556e39850, pci_type=0x555556164c06 "i440FX", host_type=0x555556163b61 "i440FX-pcihost") at /home/cloud/qemu/qemu-5.0.0/hw/i386/pc_piix.c:156
 #8  0x0000555555a4362b in machine_run_board_init (machine=0x555556e39850) at hw/core/machine.c:1140
 #9  0x00005555559749ca in qemu_init (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at /home/cloud/qemu/qemu-5.0.0/softmmu/vl.c:4897
 #10 0x000055555585cd19 in main (argc=<optimized out>, argv=<optimized out>, envp=<optimized out>) at /home/cloud/qemu/qemu-5.0.0/softmmu/main.c:48

3.VCPU運行

由于虛擬機涉及VM-Entey和VM-exit，這里從Qemu和KVM角度來分析vcpu運行主要機制。

• Qemu

|-kvm_cpu_exec
	|-kvm_arch_process_async_events
	|—cpu_exec_start
	|-kvm_arch_pre_run
	|-kvm_vcpu_ioctl            //ioctl下發KVM_RUN給KVM，進入了VM-Entry模式
	|-kvm_arch_post_run
	|-switch (run->exit_reason) //處理VM-Exit事件
		|-kvm_handle_io
		|-kvm_handle_cpuid
		|-kvm_arch_handle_exit
		|-......
		|-kvm_arch_handle_exit
	|-cpu_exec_end

1.kvm_cpu_exec中能看到一個循環，在循環中kvm_vcpu_ioctl(KVM_RUN)運行這個虛擬機，這個時候CPU進入VM-Entry即進入客戶機模式。
2.如果一直是客戶機的操作系統占用這個CPU，則會一直停留在這一行運行，一旦這個調用返回了，就說明CPU進入VM-Exit退出客戶機模式。
3.退出客戶機模式之后將CPU交還給宿主機。在循環中會對退出的原因exit_reason進行分析處理，是因為有了I/O、還是有了中斷等，并做相應的處理。處理完畢之后再次循環，再次通過VM-Entry進入客戶機模式，如此循環直到虛擬機正常或者異常退出。

• KVM

KVM: //virt/kvm/kvm_main.c
|-kvm_vcpu_ioctl                 
	|-kvm_arch_vcpu_ioctl_run    //arch/x86/kvm/x86.c
		|-vcpu_run
			|-vcpu_enter_guest
				|- 判斷是否需要退出，如果退出則設置退出的reason
				|-kvm_x86_ops->prepare_guest_switch
				|-kvm_x86_ops->run                    //進入guest模式
				|-kvm_x86_ops->handle_exit            //處理eixt，可能要退出guest模式

vcpu運行函數：
static int vcpu_run(struct kvm_vcpu *vcpu)
{
	int r;
	struct kvm *kvm = vcpu->kvm;
    ...
	for (;;) {
		if (kvm_vcpu_running(vcpu)) {
			r = vcpu_enter_guest(vcpu);
		} else {
			r = vcpu_block(kvm, vcpu);
		}
		...
	}
}

x86架構操作函數集：//arch/x86/kvm/vmx/vmx.c
static struct kvm_x86_ops vmx_x86_ops __ro_after_init = {
    ...
	.run = vmx_vcpu_run,
	.handle_exit = vmx_handle_exit,
	...
}

1.首先是Store host registers，要從宿主機模式變為客戶機模式了，所以原來宿主機運行時候的寄存器要保存下來。
2.接下來是Load guest registers，將原來客戶機運行時的寄存器加載進來。
3.接下來是Enter guest mode，調用ASM_VMX_VMLAUNCH進入客戶機模型運行，或者ASM_VMX_VMRESUME恢復客戶機模型運行。
4.如果客戶機因為某種原因退出，Save guest registers, load host registers，即保存客戶機運行的時候的寄存器，就加載宿主機運行的時候的寄存器。

4.參考資料

各種虛擬化：https://blog.csdn.net/qq_33588730/article/details/105397879