kvm vcpu run
https://luohao-brian.gitbooks.io/interrupt-virtualization/content/kvm-run-processzhi-qemu-he-xin-liu-cheng.html
kvm_cpu_thread
void *kvm_cpu_thread(void *data) { struct kvm *kvm = (struct kvm *)data; int ret = 0; kvm_reset_vcpu(kvm->vcpus); while (1) { printf("KVM start run\n"); ret = ioctl(kvm->vcpus->vcpu_fd, KVM_RUN, 0); if (ret < 0) { fprintf(stderr, "KVM_RUN failed\n"); exit(1); } switch (kvm->vcpus->kvm_run->exit_reason) { case KVM_EXIT_UNKNOWN: printf("KVM_EXIT_UNKNOWN\n"); break; case KVM_EXIT_DEBUG: printf("KVM_EXIT_DEBUG\n"); break; case KVM_EXIT_IO: printf("KVM_EXIT_IO\n"); printf("out port: %d, data: %d\n", kvm->vcpus->kvm_run->io.port, *(int *)((char *)(kvm->vcpus->kvm_run) + kvm->vcpus->kvm_run->io.data_offset) ); sleep(1); break; case KVM_EXIT_MMIO: printf("KVM_EXIT_MMIO\n"); break; case KVM_EXIT_INTR: printf("KVM_EXIT_INTR\n"); break; case KVM_EXIT_SHUTDOWN: printf("KVM_EXIT_SHUTDOWN\n"); goto exit_kvm; break; default: printf("KVM PANIC\n"); goto exit_kvm; } } exit_kvm: return 0; }
kvm->vcpus = kvm_init_vcpu(kvm, 0, kvm_cpu_thread);
struct vcpu *kvm_init_vcpu(struct kvm *kvm, int vcpu_id, void *(*fn)(void *)) { struct vcpu *vcpu = malloc(sizeof(struct vcpu)); vcpu->vcpu_id = 0; vcpu->vcpu_fd = ioctl(kvm->vm_fd, KVM_CREATE_VCPU, vcpu->vcpu_id); if (vcpu->vcpu_fd < 0) { perror("can not create vcpu"); return NULL; } vcpu->kvm_run_mmap_size = ioctl(kvm->dev_fd, KVM_GET_VCPU_MMAP_SIZE, 0); if (vcpu->kvm_run_mmap_size < 0) { perror("can not get vcpu mmsize"); return NULL; } printf("%d\n", vcpu->kvm_run_mmap_size); vcpu->kvm_run = mmap(NULL, vcpu->kvm_run_mmap_size, PROT_READ | PROT_WRITE, MAP_SHARED, vcpu->vcpu_fd, 0); if (vcpu->kvm_run == MAP_FAILED) { perror("can not mmap kvm_run"); return NULL; } vcpu->vcpu_thread_func = fn; return vcpu; }
void kvm_run_vm(struct kvm *kvm) { int i = 0; for (i = 0; i < kvm->vcpu_number; i++) { if (pthread_create(&(kvm->vcpus->vcpu_thread), (const pthread_attr_t *)NULL, kvm->vcpus[i].vcpu_thread_func, kvm) != 0) { perror("can not create kvm thread"); exit(1); } } pthread_join(kvm->vcpus->vcpu_thread, NULL); }
Qemu核心流程
阶段一：参数解析
这里使用qemu版本为qemu-kvm-1.2.0,使用Qemu工具使能虚拟机运行的命令为：
$sudo /usr/local/kvm/bin/qemu-system-x86_64 -hda vdisk_linux.img -m 1024
这时候会启动qemu-system-x86_64应用程序，该程序入口为
int main(int argc, char **argv, char **envp) <------file: vl.c,line: 2345
在main函数中第一阶段主要对命令传入的参数进行parser，包括如下几个方面：
QEMU_OPTION_M 机器类型及体系架构相关
QEMU_OPTION_hda
/mtdblock/
pflash 存储介质相关
QEMU_OPTION_numa numa系统相关
QEMU_OPTION_kernel 内核镜像相关
QEMU_OPTION_initrd initramdisk相关
QEMU_OPTION_append 启动参数相关
QEMU_OPTION_net/netdev 网络相关
QEMU_OPTION_smp smp相关
阶段二：VM的创建
通过configure_accelerator()->kvm_init() file: kvm-all.c, line: 1281;
首先打开/dev/kvm，获得三大描述符之一kvmfd， 其次通过KVM_GET_API_VERSION进行版本验证，最后通过KVM_CREATE_VM创建了一个VM对象，返回了三大描述符之二: VM描述符/vmfd。
s->fd = qemu_open("/dev/kvm", O_RDWR); kvm_init()/line: 1309
ret = kvm_ioctl(s, KVM_GET_API_VERSION, 0); kmv_init()/line: 1316
s->vmfd = kvm_ioctl(s, KVM_CREATE_VM, 0); kvm_init()/line: 1339
阶段三：VM的初始化
通过加载命令的参数的解析和相关系统的初始化，找到对应的machine类型进行第三阶段的初始化：
machine->init(ram_size, boot_devices, kernel_filename, kernel_cmdline, initrd_filename, cpu_model);
file: vl.c, line: 3651
其中的参数包括从命令行传入解析后得到的，ram的大小，内核镜像文件名，内核启动参数，initramdisk文件名，cpu模式等。
我们使用系统默认类型的machine，则init函数为pc_init_pci(),通过一系列的调用：
pc_init_pci() file: pc_piix.c, line: 294
--->pc_init1() file: pc_piix.c, line: 123
--->pc_cpus_init() file: pc.c, line: 941
在命令行启动时配置的smp参数在这里启作用了，qemu根据配置的cpu个数，进行n次的cpu初始化，相当于n个核的执行体。
void pc_cpus_init(const char *cpu_model)
{
int i;
/* init CPUs */
for(i = 0; i < smp_cpus; i++) {
pc_new_cpu(cpu_model);
}
}
继续cpu的初始化：
pc_new_cpu() file: hw/pc.c, line: 915
--->cpu_x86_init() file: target-i386/helper.c, line: 1150
--->x86_cpu_realize() file: target-i386/cpu.c, line: 1767
--->qemu_init_vcpu() file: cpus.c, line: 1039
--->qemu_kvm_start_vcpu() file: cpus.c, line: 1011
qemu_kvm_start_vcpu是一个比较重要的函数，我们在这里可以看到VM真正的执行体是什么。
阶段四：VM RUN
static void qemu_kvm_start_vcpu(CPUArchState *env) <--------file: cpus.c, line: 1011
{
CPUState *cpu = ENV_GET_CPU(env);
......
qemu_cond_init(env->halt_cond);
qemu_thread_create(cpu->thread, qemu_kvm_cpu_thread_fn, env, QEMU_THREAD_JOINABLE);
......
}
void qemu_thread_create(QemuThread *thread,
void *(*start_routine)(void*),
void *arg, int mode) <--------file: qemu-thread-posix.c, line: 118
{
......
err = pthread_attr_init(&attr);
......
err = pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
......
pthread_sigmask(SIG_SETMASK, &set, &oldset);
......
pthread_create(&thread->thread, &attr, start_routine, arg);
......
pthread_attr_destroy(&attr);
}
可以看到VM真正的执行体是QEMU进程创建的一系列POSIX线程，而线程执行函数为qemu_kvm_cpu_thread_fn。
kvm_init_vcpu()通过KVM_CREATE_VCPU创建了三大描述符之三：vcpu描述符/vcpufd。
并进入了while(1)的循环循环，反复调用kvm_cpu_exec()。
static void *qemu_kvm_cpu_thread_fn(void *arg) file: cpus.c, line: 732
{
......
r = kvm_init_vcpu(env); <--------file: kvm-all.c, line: 213
......
qemu_kvm_init_cpu_signals(env);
/* signal CPU creation */
env->created = 1;
qemu_cond_signal(&qemu_cpu_cond);
while (1) {
if (cpu_can_run(env)) {
r = kvm_cpu_exec(env); <--------file: kvm-all.c, line: 1550
if (r == EXCP_DEBUG) {
cpu_handle_guest_debug(env);
}
}
qemu_kvm_wait_io_event(env);
}
return NULL;
}
我们可以看到kvm_cpu_exec()中又是一个do()while(ret == 0)的循环体，该循环体中主要通过KVM_RUN启动VM的运行，从此处进入了kvm的内核处理阶段，并等待返回结果，同时根据返回的原因进行相关的处理，最后将处理结果返回。因为整个执行体在上述函数中也是在循环中，所以后续又会进入到该函数的处理中，而整个VM的cpu的处理就是在这个循环中不断的进行。
int kvm_cpu_exec(CPUArchState *env)
{
do {
run_ret = kvm_vcpu_ioctl(env, KVM_RUN, 0); ---------调kvm，进入内核kvm
//退出kvm,进入qemu
switch (run->exit_reason) {
case KVM_EXIT_IO:
kvm_handle_io();
......
case KVM_EXIT_MMIO:
cpu_physical_memory_rw();
......
case KVM_EXIT_IRQ_WINDOW_OPEN:
ret = EXCP_INTERRUPT;
......
case KVM_EXIT_SHUTDOWN:
ret = EXCP_INTERRUPT;
......
case KVM_EXIT_UNKNOWN:
ret = -1
......
case KVM_EXIT_INTERNAL_ERROR:
ret = kvm_handle_internal_error(env, run);
......
default:
ret = kvm_arch_handle_exit(env, run);
......
}
} while (ret == 0);
env->exit_request = 0;
return ret;
}
Conclusion
总结下kvm run在Qemu中的核心流程：
- 解析参数;
- 创建三大描述符：kvmfd/vmfd/vcpufd，及相关的初始化，为VM的运行创造必要的条件；
- 根据cpu的配置数目，启动n个POSIX线程运行VM实体，所以vm的执行环境追根溯源是在Qemu创建的线程环境中开始的。
- 通过 KVM_RUN 调用KVM提供的API发起KVM的启动，从这里进入到了内核空间运行，等待运行返回；
- 重复循环进入run阶段。
KVM核心流程
qemu通过调用kvm提供的一系列接口来启动kvm. qemu的入口为vl.c中的main函数, main函数通过调用kvm_init 和 machine->init来初始化kvm. 其中, machine->init会创建vcpu, 用一个线程去模拟vcpu, 该线程执行的函数为qemu_kvm_cpu_thread_fn, 并且该线程最终调用kvm_cpu_exec, 该函数调用kvm_vcpu_ioctl切换到kvm中,下次从kvm中返回时,会接着执行kvm_vcpu_ioctl之后的代码,判断exit_reason,然后进行相应处理.
int kvm_cpu_exec(CPUState *cpu) --> run_ret = kvm_vcpu_ioctl(cpu, KVM_RUN, 0);
当传入参数为KVM_RUN时,会进入到KVM中，会执行__vcpu_run函数，最终会调用到vcpu_enter_guest函数, vcpu_enter_guest函数中调用了kvm_x86_ops->run(vcpu), 在intel处理器架构中该函数对应的实现为vmx_vcpu_run, vmx_vcpu_run设置好寄存器状态之后调用VM_LAUNCH或者VM_RESUME进入guest vm, 一旦发生vm exit则从此处继续执行下去.
static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
{
/*vmx_vcpu_run设置好寄存器状态之后调用VM_LAUNCH或者VM_RESUME
进入guest vm, 一旦发生vm exit则从此处继续执行下去*/
asm(
/* Enter guest mode */
"jne .Llaunched \n\t"
__ex(ASM_VMX_VMLAUNCH) "\n\t"
"jmp .Lkvm_vmx_return \n\t"
".Llaunched: " __ex(ASM_VMX_VMRESUME) "\n\t"
".Lkvm_vmx_return: "
vmx->launched = 1;
/*当Guest Vm进行IO操作需要访问设备时,
就会触发vm exit 返回到vmx_vcpu_run*/
vmx_complete_interrupts(vmx);
}
static int vcpu_run(struct kvm_vcpu *vcpu) { int r; struct kvm *kvm = vcpu->kvm; vcpu->srcu_idx = srcu_read_lock(&kvm->srcu); for (;;) { if (kvm_vcpu_running(vcpu)) r = vcpu_enter_guest(vcpu);//进入虚拟机 else r = vcpu_block(kvm, vcpu); if (r <= 0) break; clear_bit(KVM_REQ_PENDING_TIMER, &vcpu->requests); if (kvm_cpu_has_pending_timer(vcpu)) kvm_inject_pending_timer_irqs(vcpu); if (dm_request_for_irq_injection(vcpu) && kvm_vcpu_ready_for_interrupt_injection(vcpu)) { r = 0; vcpu->run->exit_reason = KVM_EXIT_IRQ_WINDOW_OPEN; ++vcpu->stat.request_irq_exits; break; } kvm_check_async_pf_completion(vcpu); if (signal_pending(current)) { r = -EINTR; vcpu->run->exit_reason = KVM_EXIT_INTR; ++vcpu->stat.signal_exits; break; } if (need_resched()) { srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx); cond_resched(); vcpu->srcu_idx = srcu_read_lock(&kvm->srcu); } } srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx); return r; }
当Guest VM进行IO操作需要访问设备时,就会触发VM Exit 返回到vmx_vcpu_run, vmx保存好vmcs并且记录下VM_EXIT_REASON后返回到调用该函数的vcpu_enter_guest
vmx_complete_interrupts --> vmx->exit_reason = vmcs_read32(VM_EXIT_REASON);
回到vcpu_enter_guest中，在vcpu_enter_guest函数末尾调用了r = kvm_x86_ops->handle_exit(vcpu)，该函数对应于vmx_handle_exit函数。
static int vmx_handle_exit(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
u32 exit_reason = vmx->exit_reason;
u32 vectoring_info = vmx->idt_vectoring_info;
...
if (exit_reason < kvm_vmx_max_exit_handlers
&& kvm_vmx_exit_handlers[exit_reason])
return kvm_vmx_exit_handlers[exit_reason](vcpu);
else {
vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
vcpu->run->hw.hardware_exit_reason = exit_reason;
}
return 0;
}
vmx_handle_exit 调用kvm_vmx_exit_handlers[exit_reason](vcpu),该语句根据exit_reason调用不同的函数,该数据结构定义如下:
static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_EXCEPTION_NMI] = handle_exception,
[EXIT_REASON_EXTERNAL_INTERRUPT] = handle_external_interrupt,
[EXIT_REASON_TRIPLE_FAULT] = handle_triple_fault,
[EXIT_REASON_NMI_WINDOW] = handle_nmi_window,
[EXIT_REASON_IO_INSTRUCTION] = handle_io,
[EXIT_REASON_CR_ACCESS] = handle_cr,
[EXIT_REASON_DR_ACCESS] = handle_dr,
[EXIT_REASON_CPUID] = handle_cpuid,
[EXIT_REASON_MSR_READ] = handle_rdmsr,
[EXIT_REASON_MSR_WRITE] = handle_wrmsr,
[EXIT_REASON_PENDING_INTERRUPT] = handle_interrupt_window,
[EXIT_REASON_HLT] = handle_halt,
[EXIT_REASON_INVD] = handle_invd,
[EXIT_REASON_INVLPG] = handle_invlpg,
[EXIT_REASON_RDPMC] = handle_rdpmc,
[EXIT_REASON_VMCALL] = handle_vmcall,
[EXIT_REASON_VMCLEAR] = handle_vmclear,
[EXIT_REASON_VMLAUNCH] = handle_vmlaunch,
[EXIT_REASON_VMPTRLD] = handle_vmptrld,
[EXIT_REASON_VMPTRST] = handle_vmptrst,
[EXIT_REASON_VMREAD] = handle_vmread,
[EXIT_REASON_VMRESUME] = handle_vmresume,
[EXIT_REASON_VMWRITE] = handle_vmwrite,
[EXIT_REASON_VMOFF] = handle_vmoff,
[EXIT_REASON_VMON] = handle_vmon,
[EXIT_REASON_TPR_BELOW_THRESHOLD] = handle_tpr_below_threshold,
[EXIT_REASON_APIC_ACCESS] = handle_apic_access,
[EXIT_REASON_WBINVD] = handle_wbinvd,
[EXIT_REASON_XSETBV] = handle_xsetbv,
[EXIT_REASON_TASK_SWITCH] = handle_task_switch,
[EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation,
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
[EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
[EXIT_REASON_MWAIT_INSTRUCTION] = handle_invalid_op,
[EXIT_REASON_MONITOR_INSTRUCTION] = handle_invalid_op,
};
如果是因为IO原因导致的vm exit,则调用的处理函数为handle_io.
static int handle_io(struct kvm_vcpu *vcpu)
{
unsigned long exit_qualification;
int size, in, string;
unsigned port;
++vcpu->stat.io_exits;
exit_qualification = vmcs_readl(EXIT_QUALIFICATION); //获取exit qualification
string = (exit_qualification & 16) != 0; //判断是否为string io (ins, outs)
if (string) {
if (emulate_instruction(vcpu, 0) == EMULATE_DO_MMIO)
return 0;
return 1;
}
size = (exit_qualification & 7) + 1; //大小
in = (exit_qualification & 8) != 0; //判断io方向，是in 还是out
port = exit_qualification >> 16; //得到端口号
skip_emulated_instruction(vcpu);
return kvm_emulate_pio(vcpu, in, size, port);
}
这里我们可以看到，根据io的方向，以及是否为string io，处理方式是不同的.
int kvm_emulate_pio(struct kvm_vcpu *vcpu, int in, int size, unsigned port)
{
unsigned long val;
trace_kvm_pio(!in, port, size, 1);
vcpu->run->exit_reason = KVM_EXIT_IO;
vcpu->run->io.direction = in ? KVM_EXIT_IO_IN : KVM_EXIT_IO_OUT;
vcpu->run->io.size = vcpu->arch.pio.size = size;
vcpu->run->io.data_offset = KVM_PIO_PAGE_OFFSET * PAGE_SIZE;
vcpu->run->io.count = vcpu->arch.pio.count = vcpu->arch.pio.cur_count = 1;
vcpu->run->io.port = vcpu->arch.pio.port = port;
vcpu->arch.pio.in = in;
vcpu->arch.pio.string = 0;
vcpu->arch.pio.down = 0;
vcpu->arch.pio.rep = 0;
val = kvm_register_read(vcpu, VCPU_REGS_RAX);
memcpy(vcpu->arch.pio_data, &val, 4);
/* 如果在kmod中能完成io的话，就完成处理，不需要再返回qemu了 */
if (!kernel_pio(vcpu, vcpu->arch.pio_data)) {
complete_pio(vcpu);
return 1;
}
return 0;
}
返回qemu之后，继续kvm_cpu_exec的执行：
int kvm_cpu_exec(CPUArchState *env)
{
struct kvm_run *run = env->kvm_run;
int ret, run_ret;
…
switch (run->exit_reason) {
//根据kvm_run中存放的退出原因来选择处理方式
case KVM_EXIT_IO:
DPRINTF("handle_io\n");
kvm_handle_io(run->io.port,
(uint8_t *)run + run->io.data_offset,
run->io.direction,
run->io.size,
run->io.count);
//这里可以看到，qemu会根据kvm_run中存放的数据来进行处理了
ret = 0;
break;
…
}
static void kvm_handle_io(uint16_t port, void *data, int direction, int size, uint32_t count)
{
//在这个函数中，我们就可以看到，最终是调用了
//cpu_inb、cpu_outb这些函数和具体的设备进行交互。
int i;
uint8_t *ptr = data;
for (i = 0; i < count; i++) {
if (direction == KVM_EXIT_IO_IN) {
switch (size) {
case 1:
stb_p(ptr, cpu_inb(port));
break;
...
}
} else {
switch (size) {
case 1:
cpu_outb(port, ldub_p(ptr));
break;
...
}
ptr += size;
}
}
这样，kvm就完成了一次对guest执行out指令的虚拟。
当qemu完成IO操作后,会在kvm_cpu_exec函数的循环中,调用kvm_vcpu_ioctl重新进入kvm。
[<ffffffffb66a4d89>] schedule+0x39/0x80 [<ffffffffc0606a06>] ? kvm_irq_delivery_to_apic+0x56/0x220 [kvm] [<ffffffffb66a7447>] rwsem_down_read_failed+0xc7/0x120 [<ffffffffb63cb594>] call_rwsem_down_read_failed+0x14/0x30 [<ffffffffb66a6af7>] ? down_read+0x17/0x20 [<ffffffffc05d1480>] kvm_host_page_size+0x60/0xa0 [kvm] [<ffffffffc05ea9bc>] mapping_level+0x5c/0x130 [kvm] [<ffffffffc05f1b1b>] tdp_page_fault+0x9b/0x260 [kvm] [<ffffffffc05eba21>] kvm_mmu_page_fault+0x31/0x120 [kvm] [<ffffffffc0678db4>] handle_ept_violation+0xa4/0x170 [kvm_intel] [<ffffffffc067fd07>] vmx_handle_exit+0x257/0x490 [kvm_intel] [<ffffffffb60b2081>] ? __vtime_account_system+0x31/0x40 [<ffffffffc05e662f>] vcpu_enter_guest+0x6af/0xff0 [kvm] [<ffffffffc06034ad>] ? kvm_apic_local_deliver+0x5d/0x60 [kvm] [<ffffffffc05e8564>] kvm_arch_vcpu_ioctl_run+0xc4/0x3c0 [kvm] [<ffffffffc05cf844>] kvm_vcpu_ioctl+0x324/0x5d0 [kvm] [<ffffffffb611a4cc>] ? acct_account_cputime+0x1c/0x20 [<ffffffffb60b1f23>] ? account_user_time+0x73/0x80 [<ffffffffb61da203>] do_vfs_ioctl+0x83/0x4e0 [<ffffffffb600261f>] ? enter_from_user_mode+0x1f/0x50 [<ffffffffb6002711>] ? syscall_trace_enter_phase1+0xc1/0x110 [<ffffffffb61da6ac>] SyS_ioctl+0x4c/0x80 [<ffffffffb66a892e>] entry_SYSCALL_64_fastpath+0x12/0x7
KVM RUN的准备
当Qemu使用kvm_vcpu_ioctl(env, KVM_RUN, 0);发起KVM_RUN命令时，ioctl会陷入内核，到达kvm_vcpu_ioctl()；
kvm_vcpu_ioctl() file: virt/kvm/kvm_main.c, line: 1958
--->kvm_arch_vcpu_ioctl_run() file: arch/x86/kvm, line: 6305
--->__vcpu_run() file: arch/x86/kvm/x86.c, line: 6156
在__vcpu_run()中也出现了一个while(){}主循环；
static int __vcpu_run(struct kvm_vcpu *vcpu)
{
......
r = 1;
while (r > 0) {
if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE && !vcpu->arch.apf.halted)
r = vcpu_enter_guest(vcpu);
else {
......
}
}
if (r <= 0) <--------当r小于0时会跳出循环体,回到qemu
break;
......
}
return r;
}
我们看到当KVM通过__vcpu_run()进入主循环后，调用vcpu_enter_guest(),从名字上看可以知道这是进入guest模式的入口；
当r大于0时KVM内核代码会一直调用vcpu_enter_guest()，重复进入guest模式；
当r小于等于0时则会跳出循环体，此时会一步一步退到当初的入口kvm_vcpu_ioctl(),乃至于退回到用户态空间Qemu进程中（退出kvm,回到qemu）,具体的地方可以参看上一篇文章，这里也给出相关的代码片段：
int kvm_cpu_exec(CPUArchState *env)
{
do {
run_ret = kvm_vcpu_ioctl(env, KVM_RUN, 0);
switch (run->exit_reason) { <----------Qemu根据退出的原因进行处理，主要是IO相关方面的操作
case KVM_EXIT_IO:
kvm_handle_io(); -------------不同于handle_io
......
case KVM_EXIT_MMIO:
cpu_physical_memory_rw();
......
case KVM_EXIT_IRQ_WINDOW_OPEN:
ret = EXCP_INTERRUPT;
......
case KVM_EXIT_SHUTDOWN:
ret = EXCP_INTERRUPT;
......
case KVM_EXIT_UNKNOWN:
ret = -1
......
case KVM_EXIT_INTERNAL_ERROR:
ret = kvm_handle_internal_error(env, run);
......
default:
ret = kvm_arch_handle_exit(env, run);
......
}
} while (ret == 0);
env->exit_request = 0;
return ret;
}
Qemu根据退出的原因进行处理，主要是IO相关方面的操作，当然处理完后又会调用kvm_vcpu_ioctl(env, KVM_RUN, 0)再次RUN KMV。
我们再次拉回到内核空间，走到了static int vcpu_enter_guest(struct kvm_vcpu *vcpu)函数,其中有几个重要的初始化准备工作：
static int vcpu_enter_guest(struct kvm_vcpu *vcpu) file: arch/x86/kvm/x86.c, line: 5944
{
......
kvm_check_request(); <-------查看是否有guest退出的相关请求
......
kvm_mmu_reload(vcpu); <-------Guest的MMU初始化，为内存虚拟化做准备
......
preempt_disable(); <-------内核抢占关闭
......
kvm_x86_ops->run(vcpu); <-------体系架构相关的run操作
...... <-------到这里表明guest模式已退出
kvm_x86_ops->handle_external_intr(vcpu); <-------host处理外部中断
......
preempt_enable(); <-------内核抢占使能
......
r = kvm_x86_ops->handle_exit(vcpu); <------根据具体的退出原因进行处理
return r;
......
}
Guest的进入
kvm_x86_ops是一个x86体系相关的函数集，定义位于file: arch/x86/kvm/vmx.c, line: 8693
static struct kvm_x86_ops vmx_x86_ops = {
......
.run = vmx_vcpu_run,
.handle_exit = vmx_handle_exit,
......
}
vmx_vcpu_run()中一段核心的汇编函数的功能主要就是从ROOT模式切换至NO ROOT模式，主要进行了：
- Store host registers：主要将host状态上下文存入到VM对应的VMCS结构中；
- Load guest registers：主要讲guest状态进行加载；
- Enter guest mode: 通过ASM_VMX_VMLAUNCH指令进行VM的切换，从此进入另一个世界,即Guest OS中；
- Save guest registers, load host registers： 当发生VM Exit时，需要保持guest状态，同时加载HOST；
当第4步完成后，Guest即从NO ROOT模式退回到了ROOT模式中，又恢复了HOST的执行生涯。
Guest的退出处理
当然Guest的退出不会就这么算了，退出总是有原因的，为了保证Guest后续的顺利运行，KVM要根据退出原因进行处理，此时重要的函数为：vmx_handle_exit();
static int vmx_handle_exit(struct kvm_vcpu *vcpu) file: arch/x86/kvm/vmx.c, line: 6877
{
......
if (exit_reason < kvm_vmx_max_exit_handlers
&& kvm_vmx_exit_handlers[exit_reason])
return kvm_vmx_exit_handlers[exit_reason](vcpu); <-----根据reason调用对应的注册函数处理
else {
vcpu->run->exit_reason = KVM_EXIT_UNKNOWN;
vcpu->run->hw.hardware_exit_reason = exit_reason;
}
return 0; <--------若发生退出原因不在KVM预定义的handler范围内，则返回0
}
而众多的exit reason对应的handler如下：
static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
[EXIT_REASON_EXCEPTION_NMI] = handle_exception, <------异常
[EXIT_REASON_EXTERNAL_INTERRUPT] = handle_external_interrupt, <------外部中断
[EXIT_REASON_TRIPLE_FAULT] = handle_triple_fault,
[EXIT_REASON_NMI_WINDOW] = handle_nmi_window,
[EXIT_REASON_IO_INSTRUCTION] = handle_io, <------io指令操作
[EXIT_REASON_CR_ACCESS] = handle_cr,
[EXIT_REASON_DR_ACCESS] = handle_dr,
[EXIT_REASON_CPUID] = handle_cpuid,
[EXIT_REASON_MSR_READ] = handle_rdmsr,
[EXIT_REASON_MSR_WRITE] = handle_wrmsr,
[EXIT_REASON_PENDING_INTERRUPT] = handle_interrupt_window,
[EXIT_REASON_HLT] = handle_halt,
[EXIT_REASON_INVD] = handle_invd,
[EXIT_REASON_INVLPG] = handle_invlpg,
[EXIT_REASON_RDPMC] = handle_rdpmc,
[EXIT_REASON_VMCALL] = handle_vmcall, <-----VM相关操作指令
[EXIT_REASON_VMCLEAR] = handle_vmclear,
[EXIT_REASON_VMLAUNCH] = handle_vmlaunch,
[EXIT_REASON_VMPTRLD] = handle_vmptrld,
[EXIT_REASON_VMPTRST] = handle_vmptrst,
[EXIT_REASON_VMREAD] = handle_vmread,
[EXIT_REASON_VMRESUME] = handle_vmresume,
[EXIT_REASON_VMWRITE] = handle_vmwrite,
[EXIT_REASON_VMOFF] = handle_vmoff,
[EXIT_REASON_VMON] = handle_vmon,
[EXIT_REASON_TPR_BELOW_THRESHOLD] = handle_tpr_below_threshold,
[EXIT_REASON_APIC_ACCESS] = handle_apic_access,
[EXIT_REASON_APIC_WRITE] = handle_apic_write,
[EXIT_REASON_EOI_INDUCED] = handle_apic_eoi_induced,
[EXIT_REASON_WBINVD] = handle_wbinvd,
[EXIT_REASON_XSETBV] = handle_xsetbv,
[EXIT_REASON_TASK_SWITCH] = handle_task_switch, <----进程切换
[EXIT_REASON_MCE_DURING_VMENTRY] = handle_machine_check,
[EXIT_REASON_EPT_VIOLATION] = handle_ept_violation, <----EPT缺页异常
[EXIT_REASON_EPT_MISCONFIG] = handle_ept_misconfig,
[EXIT_REASON_PAUSE_INSTRUCTION] = handle_pause,
[EXIT_REASON_MWAIT_INSTRUCTION] = handle_invalid_op,
[EXIT_REASON_MONITOR_INSTRUCTION] = handle_invalid_op,
[EXIT_REASON_INVEPT] = handle_invept,
};
当该众多的handler处理成功后，会得到一个大于0的返回值，而处理失败则会返回一个小于0的数；则又回到__vcpu_run()中的主循环中；
vcpu_enter_guest() > 0时： 则继续循环，再次准备进入Guest模式；
vcpu_enter_guest() <= 0时： 则跳出循环，返回用户态空间，由Qemu根据退出原因进行处理。
handle_io
vmx_handle_eixt() { /* kvm_vmx_exit_handlers[exit_reason](vcpu); */ handle_io() { kvm_emulate_pio() { kernel_io() { if (read) { kvm_io_bus_read() { } } else { kvm_io_bus_write() { ioeventfd_write(); } } } } }
vmx_handle_exit-->kvm_vmx_exit_handlers[exit_reason]-->handle_io-->kvm_fast_pio_out-->emulator_pio_out_emulated-->emulator_pio_in_out-->kernel_pio-->kvm_io_bus_write-->kvm_iodevice_write(dev->ops->write)-->ioeventfd_write-->eventfd_signal
-->wake_up_locked_poll-->__wake_up_locked_key-->__wake_up_common-->vhost_poll_wakeup-->vhost_poll_queue-->vhost_work_queue-->wake_up_process
————————————————————
static int handle_io(struct kvm_vcpu *vcpu) { unsigned long exit_qualification; int size, in, string; unsigned port; exit_qualification = vmcs_readl(EXIT_QUALIFICATION); string = (exit_qualification & 16) != 0; in = (exit_qualification & 8) != 0; ++vcpu->stat.io_exits; if (string || in) return emulate_instruction(vcpu, 0) == EMULATE_DONE; port = exit_qualification >> 16; size = (exit_qualification & 7) + 1; skip_emulated_instruction(vcpu); return kvm_fast_pio_out(vcpu, size, port); }
kvm_handle_io
static void kvm_handle_io(uint16_t port, MemTxAttrs attrs, void *data, int direction, int size, uint32_t count) { int i; uint8_t *ptr = data; for (i = 0; i < count; i++) { address_space_rw(&address_space_io, port, attrs, ptr, size, direction == KVM_EXIT_IO_OUT); ptr += size; } }
#0 blk_aio_prwv (blk=0x555556a6fc60, offset=0x0, bytes=0x200, qiov=0x7ffff0059e70, co_entry=0x555555b58df1 <blk_aio_read_entry>, flags=0, cb=0x555555997813 <ide_buffered_readv_cb>, opaque=0x7ffff0059e50) at block/block-backend.c:995 #1 blk_aio_preadv (blk=0x555556a6fc60, offset=0x0, qiov=0x7ffff0059e70, flags=0, cb=0x555555997813 <ide_buffered_readv_cb>, opaque=0x7ffff0059e50) at block/block-backend.c:1100 #2 ide_buffered_readv (s=0x555557f66a68, sector_num=0x0, iov=0x555557f66d60, nb_sectors=0x1, cb=0x555555997b41 <ide_sector_read_cb>, opaque=0x555557f66a68) at hw/ide/core.c:637 #3 ide_sector_read (s=0x555557f66a68) at hw/ide/core.c:760 #4 cmd_read_pio (s=0x555557f66a68, cmd=0x20) at hw/ide/core.c:1452 #5 ide_exec_cmd (bus=0x555557f669f0, val=0x20) at hw/ide/core.c:2043 #6 ide_ioport_write (opaque=0x555557f669f0, addr=0x7, val=0x20) at hw/ide/core.c:1249 #7 portio_write (opaque=0x555558044e00, addr=0x7, data=0x20, size=0x1) at /home/jaycee/qemu-io_test/qemu-2.8.0/ioport.c:202 #8 memory_region_write_accessor (mr=0x555558044e00, addr=0x7, value=0x7ffff5f299b8, size=0x1, shift=0x0, mask=0xff, attrs=...) at /home/jaycee/qemu-io_test/qemu-2.8.0/memory.c:526 #9 access_with_adjusted_size (addr=0x7, value=0x7ffff5f299b8, size=0x1, access_size_min=0x1, access_size_max=0x4, access=0x5555557abd17 <memory_region_write_accessor>, mr=0x555558044e00, attrs=...) at /home/jaycee/qemu-io_test/qemu-2.8.0/memory.c:592 #10 memory_region_dispatch_write (mr=0x555558044e00, addr=0x7, data=0x20, size=0x1, attrs=...) at /home/jaycee/qemu-io_test/qemu-2.8.0/memory.c:1323 #11 address_space_write_continue (as=0x555556577d20 <address_space_io>, addr=0x1f7, attrs=..., buf=0x7ffff7fef000 " \237\006", len=0x1, addr1=0x7, l=0x1, mr=0x555558044e00) at /home/jaycee/qemu-io_test/qemu-2.8.0/exec.c:2608 #12 address_space_write (as=0x555556577d20 <address_space_io>, addr=0x1f7, attrs=..., buf=0x7ffff7fef000 " \237\006", len=0x1) at /home/jaycee/qemu-io_test/qemu-2.8.0/exec.c:2653 #13 address_space_rw (as=0x555556577d20 <address_space_io>, addr=0x1f7, attrs=..., buf=0x7ffff7fef000 " \237\006", len=0x1, is_write=0x1) at /home/jaycee/qemu-io_test/qemu-2.8.0/exec.c:2755 #14 kvm_handle_io (port=0x1f7, attrs=..., data=0x7ffff7fef000, direction=0x1, size=0x1, count=0x1) at /home/jaycee/qemu-io_test/qemu-2.8.0/kvm-all.c:1800 #15 kvm_cpu_exec (cpu=0x555556a802a0) at /home/jaycee/qemu-io_test/qemu-2.8.0/kvm-all.c:1958 #16 qemu_kvm_cpu_thread_fn (arg=0x555556a802a0) at /home/jaycee/qemu-io_test/qemu-2.8.0/cpus.c:998 #17 start_thread (arg=0x7ffff5f2a700) at pthread_create.c:333 #18 clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:109
2、kvm和qemu的交互
Qemu创建虚拟机进入kvm：main函数通过调用kvm_init 和 machine->init来初始化kvm. 其中, machine->init会创建vcpu, 用一个线程去模拟vcpu, 该线程执行的函数为qemu_kvm_cpu_thread_fn, 并且该线程最终kvm_cpu_exec,该函数调用kvm_vcpu_ioctl切换到kvm中。
Kvm运行并因io退出：在kvm中看到参数KVM_RUN，最后调用vcpu_enter_guest，然后 vmx_vcpu_run设置好寄存器状态之后调用VM_LAUNCH或者VM_RESUME进入guest vm。如果vm进行IO操作需要访问设备时,就会触发vm exit 返回到vmx_vcpu_run, vmx保存好vmcs并且记录下VM_EXIT_REASON后返回到调用该函数的vcpu_enter_guest, 在vcpu_enter_guest函数末尾调用了r = kvm_x86_ops->handle_exit(vcpu), 该函数对应于vmx_handle_exit函数, vmx_handle_exit 调用kvm_vmx_exit_handlers[exit_reason](vcpu),该语句根据exit_reason调用不同的函数。io操作则是handle_io把数据填充到vcpu->run，就一路return到kvm_vcpu_ioctl，就ioctl返回到qemu的kvm_cpu_exec中。
从kvm返回到qemu后的处理：Qemu在kvm_cpu_exec中会看kvm_run的run->exit_reason如果是KVM_EXIT_IO就进入kvm_handle_io里处理。 当qemu完成IO操作后,会在kvm_cpu_exec函数的循环中,调用kvm_vcpu_ioctl重新进入kvm。
kvm_run，这是用于vcpu和应用层的程序（典型如qemu)通信的一个结构，user space的 程序通过KVM__VCPU_MMAP_SIZE这个ioctl得到大小，然后映射到用户空间。
3、kvm的io处理流程
static int handle_io(struct kvm_vcpu *vcpu)
{
unsigned long exit_qualification;
int size, in, string;
unsigned port;
exit_qualification = vmcs_readl(EXIT_QUALIFICATION); //获取exit qualification
string = (exit_qualification & 16) != 0; //判断是否为string io (ins, outs)
in = (exit_qualification & 8) != 0; //判断io方向，是in 还是out
++vcpu->stat.io_exits;
if (string || in) //如果是输入类的指令，或者是string io，就进入emulator处理
return emulate_instruction(vcpu, 0) == EMULATE_DONE;
port = exit_qualification >> 16; //得到端口号
size = (exit_qualification & 7) + 1; //大小
skip_emulated_instruction(vcpu); //跳过这个指令
return kvm_fast_pio_out(vcpu, size, port); //进行out操作
}Guest执行io指令 -> 发生vmexit-> 返回qemu -> 处理io
1、out指令虚拟：虚拟单个out指令，在KVM中可以直接把out的数据返回给qemu，qemu完成out操作。
流程：KVM的handle_io->kvm_fast_pio_out->emulator_pio_out_emulated后面是vcpu->arch.pio.count = 0函数中非string类型的 out操作可以一步完成，所以从qemu处理完返回kvm后不需要再进入emulator。在emulator_pio_out_emulated中，将IO数据memcpy到kvm和qemu共享buffer中，然后emulator_pio_in_out，将相应数据保存到kvm_run中就返回到qemu的kvm_cpu_exec的switch看run->exit_reason，如果是KVM_EXIT_IO则进入kvm_handle_io中和设备交互。
2、String或in指令虚拟：如果是in指令，qemu只能把得到的数据写到kvm_run中，kvm必须在下一次vmentry的时候，将qemu得到的数据放到相应的位置，所以，在handle_io中，如果是in或者string指令，没有调用skip_emulated_instruction，这样，在qemu完成in或者一次out之后，还会在同样的地方发生vmexit，这样再由emulator完成相应的处理，针对string类型的指令，emulator会进行解码等操作，确认io的次数和源操作数、目的操作数等。
流程：handle_io->emulate_instruction->x86_emulate_instruction对指令的decode，在过程中会调用到em_in和em_out（这两个函数最后调用的emulator_pio_in_emulated中先通过和上面PIO一样的函数emulator_pio_in_out，正确返回表明qemu已经将模拟出的数据返回到参数val了，则可直接memcpy完成具体的将从qemu中得到的数据写到正确位置vcpu->arch.pio_data），设置如果是out，下次到KVM时直接进入emulator，如果是in，注册vcpu->arch.complete_userspace_io = complete_emulated_pio;需要在下次qemu进入kvm的时候，完成io，实际上就是将qemu得到的数据写到正确的位置。下次进入kvm，如果要完成in指令，会在函数kvm_arch_vcpu_ioctl_run中调用注册的complete_emulated_pio会再次调用emulate_instruction将数据写到正确位置（这次不用解码，而是直接em_in）。
- 在guest中，virtio-blk的初始化或者说是在探测virtio-blk之前
virtio_dev_probe
|-->add_status
|-->dev->config->set_status[vp_set_status]
|-->iowrite8(status, vp_dev->ioaddr + VIRTIO_PCI_STATUS)
这里就产生VM exit到Qemu中了，而在Qemu中有如下的处理：-
Qemu中建立ioeventfd的处理流程：
virtio_pci_config_write
|-->virtio_ioport_write
|-->virtio_pci_start_ioeventfd
|-->virtio_pci_set_host_notifier_internal
|-->virtio_queue_set_host_notifier_fd_handler
|-->memory_region_add_eventfd
|-->memory_region_transaction_commit
|-->address_space_update_ioeventfds
|-->address_space_add_del_ioeventfds
|-->eventfd_add[kvm_mem_ioeventfd_add]
|-->kvm_set_ioeventfd_mmio
|-->kvm_vm_ioctl(...,KVM_IOEVENTFD,...)
最后这一步就切换到kvm内核模块中来通过KVM_IOEVENT来建立ioeventfd：
kvm内核模块中建立ioeventfd：
kvm_ioeventfd
|-->kvm_assign_ioeventfd在这个流程中为某段区域建立了一个ioeventfd，这样的话guest在操作这块区域的时候就会触发ioeventfd（这是fs的eventfd机制），从而通知到Qemu，Qemu的main loop原先是阻塞的，现在有ioevent发生之后就可以得到运行了，也就可以做对virtio-blk相应的处理了。
KVm 使用ioeventfd
那么当guest对该块区域内存区域进行写的时候，势必会先exit到kvm内核模块中，kvm内核模块又是怎么知道这块区域是注册了event的呢？是怎么个流程呢？
只使用EPT的情况下，guest对一块属于MMIO的区域进行读写操作引起的exit在kvm中对应的处理函数是handle_ept_misconfig，下面就看下具体的流程：
handle_ept_misconfig
|-->x86_emulate_instruction
|-->x86_emulate_insn
|-->writeback
|-->segmented_write
|-->write_emulated[emulator_write_emulated]
|-->emulator_read_write
|-->emulator_read_write_onepage
|-->ops->read_write_mmio[write_mmio]
|-->vcpu_mmio_write
|-->kvm_io_bus_write
|-->__kvm_io_bus_write
|-->kvm_iodevice_write
|-->ops->write[ioeventfd_write]
在ioeventfd_write函数中会调用文件系统eventfd机制的eventfd_signal函数来触发相应的事件。
上述就是整个ioeventfd从创建到触发的流程！！！！
Conclusion
至此，KVM内核代码部分的核心调用流程的分析到此结束，从上述流程中可以看出，KVM内核代码的主要工作如下：
- Guest进入前的准备工作；
- Guest的进入；
- 根据Guest的退出原因进行处理，若kvm自身能够处理的则自行处理；若KVM无法处理，则返回到用户态空间的Qemu进程中进行处理；
总而言之，KVM与Qemu的工作是为了确保Guest的正常运行，通过各种异常的处理，使Guest无需感知其运行的虚拟环境。
