KVM虚拟化原理-创建KVM

kvm这个结构体包含了vCPU，内存，APIC，IRQ，MMU，Event事件管理等信息。该结构体中的信息主要在kvm虚拟机内部使用，用于跟踪虚拟机的状态。
对于一个kvm，就对应一个线程。
Kvm完全利用了硬件虚拟化技术，通过cat /proc/cpuinfo 查看信息，如果是intel处理器，那么就加载kvm-intel.ko
用户态创建一个虚拟机就是通过ioctl向/dev/kvm字符设备进行设置和管理kvm的。

struct kvm {
    spinlock_t mmu_lock;
    spinlock_t requests_lock;
    struct rw_semaphore slots_lock;
    struct mm_struct *mm; /* userspace tied to this vm */
    int nmemslots;
    struct kvm_memory_slot memslots[KVM_MEMORY_SLOTS +
                    KVM_PRIVATE_MEM_SLOTS];
#ifdef CONFIG_KVM_APIC_ARCHITECTURE
    u32 bsp_vcpu_id;
    struct kvm_vcpu *bsp_vcpu;
#endif
    struct kvm_vcpu *vcpus[KVM_MAX_VCPUS];
    atomic_t online_vcpus;
    struct list_head vm_list;
    struct mutex lock;
    struct kvm_io_bus mmio_bus;
    struct kvm_io_bus pio_bus;
#ifdef CONFIG_HAVE_KVM_EVENTFD
    struct {
        spinlock_t        lock;
        struct list_head  items;
    } irqfds;
    struct list_head ioeventfds;
#endif
    struct kvm_vm_stat stat;
    struct kvm_arch arch;
    atomic_t users_count;
#ifdef KVM_COALESCED_MMIO_PAGE_OFFSET
    struct kvm_coalesced_mmio_dev *coalesced_mmio_dev;
    struct kvm_coalesced_mmio_ring *coalesced_mmio_ring;
#endif

    struct mutex irq_lock;
#ifdef CONFIG_HAVE_KVM_IRQCHIP
    struct list_head irq_routing; /* of kvm_kernel_irq_routing_entry */
    struct hlist_head mask_notifier_list;
#endif

#ifdef KVM_ARCH_WANT_MMU_NOTIFIER
    struct mmu_notifier mmu_notifier;
    unsigned long mmu_notifier_seq;
    long mmu_notifier_count;
#endif
};

struct kvm_vm_stat stat;就是KVM虚拟机中的页表、MMU等运行时状态信息。
kvm_x86_ops 结构体中的所有成员都是函数指针，在kvm-intel.ko 和 kvm-amd.ko这两个不同的模块中，针对各自体系做不同的函数。KVM子系统代码将通过该结构体函数进行实际的硬件操作。

针对kvm的fd，通过KVM_CREATE_VCPU指令字可以创建KVM的vCPU，并且获得该vcpu_fd,vcpu_fd的操作主要包含在kvm_vcpu_fops中，kvm_vcpu_fops的实现方法如下：

static struct file_operations kvm_vcpu_fops = {
    .release = kvm_vcpu_release,
    .unlocked_ioctl = kvm_vcpu_ioctl,
    .compat_ioctl = kvm_vcpu_ioctl,
    .mmap = kvm_vcpu_mmap,
};