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1、基本原理
KVM虚拟机通过字符设备/dev/kvm的ioctl接口创建和运行，相关原理见之前的文章说明。
虚拟机的运行通过/dev/kvm设备ioctl VCPU接口的KVM_RUN指令实现，在VM和VCPU创建好并完成初始化后，就可以调度该虚拟机运行了，通常，一个VCPU对应于一个线程，虚拟机运行的本质为调度该虚拟机相关的VCPU所在线程运行。虚拟机(VCPU)的运行主要任务是要进行上下文切换，上下文主要包括相关寄存器、APIC状态、TLB等，通常上下文切换的过程如下：
1、 保存当前的上下文。
2、 使用kvm_vcpu结构体中的上下文信息，加载到物理CPU中。
3、 执行kvm_x86_ops中的run_vcpu函数，调用硬件相关的指令(如VMLAUNCH)，进入虚拟机运行环境中。
虚拟机运行于qemu-kvm的进程上下文中，从硬件的角度看，虚拟机的运行过程，实质为相关指令的执行过程，虚拟机编译后的也就是相应的CPU指令序列，而虚拟机的指令跟Host机的指令执行过程并没有太多的差别，最关键的差别为“敏感指令”(通常为IO、内存等关键操作)的执行，这也是虚拟化实现的本质所在，当在虚拟机中(Guest模式)执行“敏感指令”时，会触发（由硬件触发）VM-exit，使当前CPU从Guest模式(non-root模式)切换到root模式，当前CPU的控制权随之转交给VMM(Hypervisor，KVM中即Host)，由VMM进行相应的处理，处理完成后再次通过应该硬件指令(如VMLAUNCH)，重新进入到Guest模式，从而进入虚拟机运行环境中继续运行。
本文简单解释及分析在3.10版本内核代码中的相关流程，用户态qemu-kvm部分暂不包括。
2、大致流程：
Qemu-kvm可以通过ioctl(KVM_RUN…)使虚拟机运行，最终进入内核态，由KVM相关内核流程处理，在内核态执行的大致过程如下：
kvm_vcpu_ioctl -->
kvm_arch_vcpu_ioctl_run
具体由内核函数kvm_arch_vcpu_ioctl_run完成相关工作。主要流程如下：
1、 Sigprocmask()屏蔽信号，防止在此过程中受到信号的干扰。
2、 设置当前VCPU状态为KVM_MP_STATE_UNINITIALIZED
3、 配置APIC和mmio相关信息
4、 将VCPU中保存的上下文信息写入指定位置
5、 然后的工作交由__vcpu_run完成
6、 __vcpu_run最终调用vcpu_enter_guest，该函数实现了进入Guest，并执行Guest OS具体指令的操作。
7、 vcpu_enter_guest最终调用kvm_x86_ops中的run函数运行。对应于Intel平台，该函数为vmx_vcpu_run(设置Guest CR3和其他寄存器、EPT/影子页表相关设置、汇编代码VMLAUNCH切换到非根模式，执行Guest目标代码)。
8、 Guest代码执行到敏感指令或因其他原因(比如中断/异常)，VM-Exit退出非根模式，返回到vcpu_enter_guest函数继续执行。
9、 vcpu_enter_guest函数中会判断VM-Exit原因，并进行相应处理。
10、处理完成后VM-Entry到Guest重新执行Guest代码，或重新等待下次调度。
3、代码分析
kvm_vcpu_ioctl():
- /*
- * kvm ioctl VCPU指令的入口，传入的fd为KVM_CREATE_VCPU中返回的fd。
- * 主要针对具体的VCPU进行参数设置。如：相关寄存器的读
- * 写、中断控制等
- */
- static long kvm_vcpu_ioctl(struct file *filp,
- unsigned int ioctl, unsigned long arg)
- {
- struct kvm_vcpu *vcpu = filp->private_data;
- void __user *argp = (void __user *)arg;
- int r;
- struct kvm_fpu *fpu = NULL;
- struct kvm_sregs *kvm_sregs = NULL;
- if (vcpu->kvm->mm != current->mm)
- return -EIO;
- #if defined(CONFIG_S390) || defined(CONFIG_PPC) || defined(CONFIG_MIPS)
- /*
- * Special cases: vcpu ioctls that are asynchronous to vcpu execution,
- * so vcpu_load() would break it.
- */
- if (ioctl == KVM_S390_INTERRUPT || ioctl == KVM_INTERRUPT)
- return kvm_arch_vcpu_ioctl(filp, ioctl, arg);
- #endif
- // KVM虚拟机VCPU数据结构载入物理CPU
- r = vcpu_load(vcpu);
- if (r)
- return r;
- switch (ioctl) {
- /*
- * 运行虚拟机，最终通过执行VMLAUNCH指令进入non root模式，
- * 进入虚拟机运行。当虚拟机内部执行敏感指令时，由硬
- * 件触发VM-exit，返回到root模式
- */
- case KVM_RUN:
- r = -EINVAL;
- // 不能带参数。
- if (arg)
- goto out;
- // 运行VCPU(即运行虚拟机)的入口函数
- r = kvm_arch_vcpu_ioctl_run(vcpu, vcpu->run);
- trace_kvm_userspace_exit(vcpu->run->exit_reason, r);
- break;
- ...
kvm_vcpu_ioctl()-->kvm_arch_vcpu_ioctl_run()-->__vcpu_run():
- static int __vcpu_run(struct kvm_vcpu *vcpu)
- {
- int r;
- struct kvm *kvm = vcpu->kvm;
- vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
- /*设置vcpu->arch.apic->vapic_page*/
- r = vapic_enter(vcpu);
- if (r) {
- srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
- return r;
- }
- r = 1;
- while (r > 0) {
- /*检查状态*/
- if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
- !vcpu->arch.apf.halted)
- /* 进入Guest模式，最终通过VMLAUNCH指令实现*/
- r = vcpu_enter_guest(vcpu);
- else {/*什么情况下会走到这里?*/
- srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
- /*阻塞VCPU，其实就是schddule()调度出去，但在有特殊情况时(比如有挂起的定时器或信号时)，不进行调度而直接退出*/
- kvm_vcpu_block(vcpu);
- vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
- if (kvm_check_request(KVM_REQ_UNHALT, vcpu)) {
- kvm_apic_accept_events(vcpu);
- switch(vcpu->arch.mp_state) {
- case KVM_MP_STATE_HALTED:
- vcpu->arch.pv.pv_unhalted = false;
- vcpu->arch.mp_state =
- KVM_MP_STATE_RUNNABLE;
- case KVM_MP_STATE_RUNNABLE:
- vcpu->arch.apf.halted = false;
- break;
- case KVM_MP_STATE_INIT_RECEIVED:
- break;
- default:
- r = -EINTR;
- break;
- }
- }
- }
- if (r requests);
- if (kvm_cpu_has_pending_timer(vcpu))
- kvm_inject_pending_timer_irqs(vcpu);
- if (dm_request_for_irq_injection(vcpu)) {
- r = -EINTR;
- vcpu->run->exit_reason = KVM_EXIT_INTR;
- ++vcpu->stat.request_irq_exits;
- }
- kvm_check_async_pf_completion(vcpu);
- if (signal_pending(current)) {
- r = -EINTR;
- vcpu->run->exit_reason = KVM_EXIT_INTR;
- ++vcpu->stat.signal_exits;
- }
- /*这是kvm中的一个调度时机点，即选择新VCPU运行的时机点*/
- if (need_resched()) {
- srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
- kvm_resched(vcpu);
- vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
- }
- }
- srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
- vapic_exit(vcpu);
- return r;
- }
kvm_vcpu_ioctl()-->kvm_arch_vcpu_ioctl_run()-->__vcpu_run()-->vcpu_enter_guest():
- /* 进入Guest模式，最终通过VMLAUNCH指令实现*/
- static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
- {
- int r;
- bool req_int_win = !irqchip_in_kernel(vcpu->kvm) &&
- vcpu->run->request_interrupt_window;
- bool req_immediate_exit = false;
- /*进入Guest模式前先处理相关挂起的请求*/
- if (vcpu->requests) {
- /*卸载MMU*/
- if (kvm_check_request(KVM_REQ_MMU_RELOAD, vcpu))
- kvm_mmu_unload(vcpu);
- /*定时器迁移*/
- if (kvm_check_request(KVM_REQ_MIGRATE_TIMER, vcpu))
- __kvm_migrate_timers(vcpu);
- /*主时钟更新*/
- if (kvm_check_request(KVM_REQ_MASTERCLOCK_UPDATE, vcpu))
- kvm_gen_update_masterclock(vcpu->kvm);
- /*全局时钟更新*/
- if (kvm_check_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu))
- kvm_gen_kvmclock_update(vcpu);
- /*虚拟机时钟更新*/
- if (kvm_check_request(KVM_REQ_CLOCK_UPDATE, vcpu)) {
- r = kvm_guest_time_update(vcpu);
- if (unlikely(r))
- goto out;
- }
- /*更新mmu*/
- if (kvm_check_request(KVM_REQ_MMU_SYNC, vcpu))
- kvm_mmu_sync_roots(vcpu);
- /*刷新TLB*/
- if (kvm_check_request(KVM_REQ_TLB_FLUSH, vcpu))
- kvm_x86_ops->tlb_flush(vcpu);
- if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
- vcpu->run->exit_reason = KVM_EXIT_TPR_ACCESS;
- r = 0;
- goto out;
- }
- if (kvm_check_request(KVM_REQ_TRIPLE_FAULT, vcpu)) {
- vcpu->run->exit_reason = KVM_EXIT_SHUTDOWN;
- r = 0;
- goto out;
- }
- if (kvm_check_request(KVM_REQ_DEACTIVATE_FPU, vcpu)) {
- vcpu->fpu_active = 0;
- kvm_x86_ops->fpu_deactivate(vcpu);
- }
- if (kvm_check_request(KVM_REQ_APF_HALT, vcpu)) {
- /* Page is swapped out. Do synthetic halt */
- vcpu->arch.apf.halted = true;
- r = 1;
- goto out;
- }
- if (kvm_check_request(KVM_REQ_STEAL_UPDATE, vcpu))
- record_steal_time(vcpu);
- if (kvm_check_request(KVM_REQ_NMI, vcpu))
- process_nmi(vcpu);
- if (kvm_check_request(KVM_REQ_PMU, vcpu))
- kvm_handle_pmu_event(vcpu);
- if (kvm_check_request(KVM_REQ_PMI, vcpu))
- kvm_deliver_pmi(vcpu);
- if (kvm_check_request(KVM_REQ_SCAN_IOAPIC, vcpu))
- vcpu_scan_ioapic(vcpu);
- }
- // 检查是否有事件请求
- if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
- kvm_apic_accept_events(vcpu);
- if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
- r = 1;
- goto out;
- }
- // 注入阻塞的事件，中断，异常和nmi等
- inject_pending_event(vcpu);
- /* enable NMI/IRQ window open exits if needed */
- /*
- * 使能NMI/IRQ window，参见Intel64 System Programming Guide 25.3节
- * 当使能了interrupt-window exiting或NMI-window exiting(由VMCS中相关字段控制)，
- * 表示在刚进入虚拟机后，就会立刻因为有pending或注入的中断导致VM-exit
- */
- if (vcpu->arch.nmi_pending)
- req_immediate_exit =
- kvm_x86_ops->enable_nmi_window(vcpu) != 0;
- else if (kvm_cpu_has_injectable_intr(vcpu) || req_int_win)
- req_immediate_exit =
- kvm_x86_ops->enable_irq_window(vcpu) != 0;
- if (kvm_lapic_enabled(vcpu)) {
- /*
- * Update architecture specific hints for APIC
- * virtual interrupt delivery.
- */
- if (kvm_x86_ops->hwapic_irr_update)
- kvm_x86_ops->hwapic_irr_update(vcpu,
- kvm_lapic_find_highest_irr(vcpu));
- update_cr8_intercept(vcpu);
- kvm_lapic_sync_to_vapic(vcpu);
- }
- }
- // 装载MMU，待深入分析
- r = kvm_mmu_reload(vcpu);
- if (unlikely(r)) {
- goto cancel_injection;
- }
- preempt_disable();
- // 进入Guest前期准备，架构相关
- kvm_x86_ops->prepare_guest_switch(vcpu);
- if (vcpu->fpu_active)
- kvm_load_guest_fpu(vcpu);
- kvm_load_guest_xcr0(vcpu);
- vcpu->mode = IN_GUEST_MODE;
- /* We should set ->mode before check ->requests,
- * see the comment in make_all_cpus_request.
- */
- smp_mb();
- local_irq_disable();
- /*
- * 如果VCPU处于EXITING_GUEST_MODE或者vcpu->requests(?)或者需要调度或者
- * 有挂起的信号，则放弃
- */
- if (vcpu->mode == EXITING_GUEST_MODE || vcpu->requests
- || need_resched() || signal_pending(current)) {
- vcpu->mode = OUTSIDE_GUEST_MODE;
- smp_wmb();
- local_irq_enable();
- preempt_enable();
- r = 1;
- goto cancel_injection;
- }
- srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
- // req_immediate_exit在前面使能NMI/IRQ window失败时设置，此时需要立即退出，触发重新调度
- if (req_immediate_exit)
- smp_send_reschedule(vcpu->cpu);
- // 计算虚拟机的enter时间
- kvm_guest_enter();
- // 调试相关
- if (unlikely(vcpu->arch.switch_db_regs)) {
- set_debugreg(0, 7);
- set_debugreg(vcpu->arch.eff_db[0], 0);
- set_debugreg(vcpu->arch.eff_db[1], 1);
- set_debugreg(vcpu->arch.eff_db[2], 2);
- set_debugreg(vcpu->arch.eff_db[3], 3);
- }
- trace_kvm_entry(vcpu->vcpu_id);
- // 调用架构相关的run接口(vmx_vcpu_run)，进入Guest模式
- kvm_x86_ops->run(vcpu);
-
- // 此处开始，说明已经发生了VM-exit，退出了Guest模式
- /*
- * If the guest has used debug registers, at least dr7
- * will be disabled while returning to the host.
- * If we don't have active breakpoints in the host, we don't
- * care about the messed up debug address registers. But if
- * we have some of them active, restore the old state.
- */
- if (hw_breakpoint_active())
- hw_breakpoint_restore();
- /*记录Guest退出前的TSC时钟*/
- vcpu->arch.last_guest_tsc = kvm_x86_ops->read_l1_tsc(vcpu,
- native_read_tsc());
- // 设置模式
- vcpu->mode = OUTSIDE_GUEST_MODE;
- smp_wmb();
- /* Interrupt is enabled by handle_external_intr() */
- kvm_x86_ops->handle_external_intr(vcpu);
- ++vcpu->stat.exits;
- /*
- * We must have an instruction between local_irq_enable() and
- * kvm_guest_exit(), so the timer interrupt isn't delayed by
- * the interrupt shadow. The stat.exits increment will do nicely.
- * But we need to prevent reordering, hence this barrier():
- */
- barrier();
- // 计算虚拟机的退出时间，其中还开中断了?
- kvm_guest_exit();
-
- preempt_enable();
- vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
- /*
- * Profile KVM exit RIPs:
- */
- // Profile(采样计数，用于性能分析和调优)相关
- if (unlikely(prof_on == KVM_PROFILING)) {
- unsigned long rip = kvm_rip_read(vcpu);
- profile_hit(KVM_PROFILING, (void *)rip);
- }
- if (unlikely(vcpu->arch.tsc_always_catchup))
- kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
- if (vcpu->arch.apic_attention)
- kvm_lapic_sync_from_vapic(vcpu);
- /*
- * 调用vmx_handle_exit()处理虚拟机异常，异常原因及其它关键信息
- * 已经在之前获取。
- */
- r = kvm_x86_ops->handle_exit(vcpu);
- return r;
- cancel_injection:
- kvm_x86_ops->cancel_injection(vcpu);
- if (unlikely(vcpu->arch.apic_attention))
- kvm_lapic_sync_from_vapic(vcpu);
- out:
- return r;
- }
kvm_vcpu_ioctl()-->kvm_arch_vcpu_ioctl_run()-->__vcpu_run()-->vcpu_enter_guest()-->vmx_vcpu_run():
/*
* 运行虚拟机，进入Guest模式，即non root模式
*/
static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
unsigned long debugctlmsr;
/* Record the guest's net vcpu time for enforced NMI injections. */
// nmi注入?跟nmi_watchdog相关?
if (unlikely(!cpu_has_virtual_nmis() && vmx->soft_vnmi_blocked))
vmx->entry_time = ktime_get();
/* Don't enter VMX if guest state is invalid, let the exit handler
start emulation until we arrive back to a valid state */
if (vmx->emulation_required)
return;
if (vmx->nested.sync_shadow_vmcs) {
copy_vmcs12_to_shadow(vmx);
vmx->nested.sync_shadow_vmcs = false;
}
// 写入Guest的RSP寄存器信息至VMCS相关位置中
if (test_bit(VCPU_REGS_RSP, (unsigned long *)&vcpu->arch.regs_dirty))
vmcs_writel(GUEST_RSP, vcpu->arch.regs[VCPU_REGS_RSP]);
// 写入Guest的RIP寄存器信息至VMCS相关位置中
if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty))
vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
/* When single-stepping over STI and MOV SS, we must clear the
* corresponding interruptibility bits in the guest state. Otherwise
* vmentry fails as it then expects bit 14 (BS) in pending debug
* exceptions being set, but that's not correct for the guest debugging
* case. */
// 单步调试时，需要禁用Guest中断
if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
vmx_set_interrupt_shadow(vcpu, 0);
atomic_switch_perf_msrs(vmx);
debugctlmsr = get_debugctlmsr();
// vmx->__launched用于判断当前VCPU是否已经VMLAUNCH了
vmx->__launched = vmx->loaded_vmcs->launched;
// 执行VMLAUNCH指令进入Guest模式，虚拟机开始运行
asm(
/* Store host registers */
/*将相关寄存器压栈*/
"push %%" _ASM_DX "; push %%" _ASM_BP ";"/*BP压栈*/
/*为guest的rcx寄存器保留个位置，所以这里压两次栈*/
"push %%" _ASM_CX " \n\t" /* placeholder for guest rcx */
"push %%" _ASM_CX " \n\t"
/*
* %c表示用来表示使用立即数替换，但不使用立即数的语法，at&t汇编中表示立即数的语法前面有一个$，而用了%c后，就去掉了这个$。
* 主要是用在间接寻址的情况，这种情况下如果直接使用$立即数的方式的话，会报语法错误。
* [host_rsp]是后面输入部分定义的tag，使用%tag方式可以直接引用，%0是后面输入输出部分中的第一个操作数，即vmx，这里是间接寻址
* %c[host_rsp](%0)整体来看就是vmx(以寄存器ecx传入)中的host_rsp成员。
* 所以，如下语句的整体含义就是比较当前SP寄存器和vmx->host_rsp的值。
*/
/*如果当前RSP和vmx->rsp相等，那就不用mov了，否则将当前RSP保存到vmx中*/
"cmp %%" _ASM_SP ", %c[host_rsp](%0) \n\t"
"je 1f \n\t"
"mov %%" _ASM_SP ", %c[host_rsp](%0) \n\t"
/*执行ASM_VMX_VMWRITE_RSP_RDX指令，当出现异常时直接重启，由__ex()实现*/
__ex(ASM_VMX_VMWRITE_RSP_RDX) "\n\t"
"1: \n\t"
/* Reload cr2 if changed */
/*比较当前CR2寄存器和vmx中保存的CR2寄存器内容，如果不相等，就从vmx中重新CR2内容到当前CR2寄存器中*/
"mov %c[cr2](%0), %%" _ASM_AX " \n\t"
"mov %%cr2, %%" _ASM_DX " \n\t"
"cmp %%" _ASM_AX ", %%" _ASM_DX " \n\t"
"je 2f \n\t"
"mov %%" _ASM_AX", %%cr2 \n\t"
"2: \n\t"
/* Check if vmlaunch of vmresume is needed */
/*判断vcpu_vmx->__launched，确认是否需要执行VMLAUNCH*/
"cmpl $0, %c[launched](%0) \n\t"
/* Load guest registers. Don't clobber flags. */
/*加载guest寄存器，其实就是从vmx中加载*/
"mov %c[rax](%0), %%" _ASM_AX " \n\t"
"mov %c[rbx](%0), %%" _ASM_BX " \n\t"
"mov %c[rdx](%0), %%" _ASM_DX " \n\t"
"mov %c[rsi](%0), %%" _ASM_SI " \n\t"
"mov %c[rdi](%0), %%" _ASM_DI " \n\t"
"mov %c[rbp](%0), %%" _ASM_BP " \n\t"
#ifdef CONFIG_X86_64
"mov %c[r8](%0), %%r8 \n\t"
"mov %c[r9](%0), %%r9 \n\t"
"mov %c[r10](%0), %%r10 \n\t"
"mov %c[r11](%0), %%r11 \n\t"
"mov %c[r12](%0), %%r12 \n\t"
"mov %c[r13](%0), %%r13 \n\t"
"mov %c[r14](%0), %%r14 \n\t"
"mov %c[r15](%0), %%r15 \n\t"
#endif
"mov %c[rcx](%0), %%" _ASM_CX " \n\t" /* kills %0 (ecx) */
/* Enter guest mode */
"jne 1f \n\t"
/* 执行VMLAUNCH指令，进入Guest模式*/
__ex(ASM_VMX_VMLAUNCH) "\n\t"
"jmp 2f \n\t"
/* 执行VMRESUME指令，从Guest模式恢复到root模式*/
"1: " __ex(ASM_VMX_VMRESUME) "\n\t"
"2: "
/* Save guest registers, load host registers, keep flags */
"mov %0, %c[wordsize](%%" _ASM_SP ") \n\t"
"pop %0 \n\t"
"mov %%" _ASM_AX ", %c[rax](%0) \n\t"
"mov %%" _ASM_BX ", %c[rbx](%0) \n\t"
__ASM_SIZE(pop) " %c[rcx](%0) \n\t"
"mov %%" _ASM_DX ", %c[rdx](%0) \n\t"
"mov %%" _ASM_SI ", %c[rsi](%0) \n\t"
"mov %%" _ASM_DI ", %c[rdi](%0) \n\t"
"mov %%" _ASM_BP ", %c[rbp](%0) \n\t"
#ifdef CONFIG_X86_64
"mov %%r8, %c[r8](%0) \n\t"
"mov %%r9, %c[r9](%0) \n\t"
"mov %%r10, %c[r10](%0) \n\t"
"mov %%r11, %c[r11](%0) \n\t"
"mov %%r12, %c[r12](%0) \n\t"
"mov %%r13, %c[r13](%0) \n\t"
"mov %%r14, %c[r14](%0) \n\t"
"mov %%r15, %c[r15](%0) \n\t"
#endif
"mov %%cr2, %%" _ASM_AX " \n\t"
"mov %%" _ASM_AX ", %c[cr2](%0) \n\t"
"pop %%" _ASM_BP "; pop %%" _ASM_DX " \n\t"
"setbe %c[fail](%0) \n\t"
".pushsection .rodata \n\t"
".global vmx_return \n\t"
"vmx_return: " _ASM_PTR " 2b \n\t"
".popsection"
: : "c"(vmx), "d"((unsigned long)HOST_RSP),
[launched]"i"(offsetof(struct vcpu_vmx, __launched)),
[fail]"i"(offsetof(struct vcpu_vmx, fail)),
/*[host_rsp]是tag，可以在前面以%[host_rsp]方式引用*/
[host_rsp]"i"(offsetof(struct vcpu_vmx, host_rsp)),
[rax]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RAX])),
[rbx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBX])),
[rcx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RCX])),
[rdx]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RDX])),
[rsi]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RSI])),
[rdi]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RDI])),
[rbp]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_RBP])),
#ifdef CONFIG_X86_64
[r8]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R8])),
[r9]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R9])),
[r10]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R10])),
[r11]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R11])),
[r12]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R12])),
[r13]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R13])),
[r14]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R14])),
[r15]"i"(offsetof(struct vcpu_vmx, vcpu.arch.regs[VCPU_REGS_R15])),
#endif
[cr2]"i"(offsetof(struct vcpu_vmx, vcpu.arch.cr2)),
[wordsize]"i"(sizeof(ulong))
: "cc", "memory"/*clobber list，cc表示寄存器，memory表示内存*/
#ifdef CONFIG_X86_64
, "rax", "rbx", "rdi", "rsi"
, "r8", "r9", "r10", "r11", "r12", "r13", "r14", "r15"
#else
, "eax", "ebx", "edi", "esi"
#endif
);
// 运行到这里，说明已经发生了VM-exit，返回到了root模式
/* MSR_IA32_DEBUGCTLMSR is zeroed on vmexit. Restore it if needed */
if (debugctlmsr)
update_debugctlmsr(debugctlmsr);
#ifndef CONFIG_X86_64
/*
* The sysexit path does not restore ds/es, so we must set them to
* a reasonable value ourselves.
*
* We can't defer this to vmx_load_host_state() since that function
* may be executed in interrupt context, which saves and restore segments
* around it, nullifying its effect.
*/
/*重新加载ds/es段寄存器，因为VM-exit不会自动加载他们*/
loadsegment(ds, __USER_DS);
loadsegment(es, __USER_DS);
#endif
vcpu->arch.regs_avail = ~((1 |
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