简单介绍 Linux 内核的 KVM 模块，以 MIPS 体系结构为例，内核源码版本为 5.10.42。
KVM (Kernel-based Virtual Machine)#
KVM 是一个完整的虚拟化解决方案，允许用户在特定机器上用虚拟机直接运行未经修改的 Linux 内核。
KVM 通常和 QEMU 结合使用，见 QEMU 简介。
KVM 的 API 接口可以参考内核文档。
KVM 模块有体系结构相关和无关的两部分，简单起见，体系结构相关的部分只考虑 MIPS 的代码，选用内核源码版本为 5.10.42。
模块初始化#
arch/mips/kvm/mips.c：
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| static int __init kvm_mips_init(void)
{
int ret;
if (cpu_has_mmid) {
pr_warn("KVM does not yet support MMIDs. KVM Disabled\n");
return -EOPNOTSUPP;
}
ret = kvm_mips_entry_setup();
if (ret)
return ret;
ret = kvm_init(NULL, sizeof(struct kvm_vcpu), 0, THIS_MODULE);
if (ret)
return ret;
if (boot_cpu_type() == CPU_LOONGSON64)
kvm_priority_to_irq = kvm_loongson3_priority_to_irq;
register_die_notifier(&kvm_mips_csr_die_notifier);
return 0;
}
module_init(kvm_mips_init);
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kvm_mips_init() 函数会调用体系结构无关的初始化函数 kvm_init()。
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| int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
struct module *module)
{
struct kvm_cpu_compat_check c;
int r;
int cpu;
r = kvm_arch_init(opaque);
if (r)
goto out_fail;
/*
* kvm_arch_init makes sure there's at most one caller
* for architectures that support multiple implementations,
* like intel and amd on x86.
* kvm_arch_init must be called before kvm_irqfd_init to avoid creating
* conflicts in case kvm is already setup for another implementation.
*/
r = kvm_irqfd_init();
if (r)
goto out_irqfd;
if (!zalloc_cpumask_var(&cpus_hardware_enabled, GFP_KERNEL)) {
r = -ENOMEM;
goto out_free_0;
}
r = kvm_arch_hardware_setup(opaque);
if (r < 0)
goto out_free_1;
c.ret = &r;
c.opaque = opaque;
for_each_online_cpu(cpu) {
smp_call_function_single(cpu, check_processor_compat, &c, 1);
if (r < 0)
goto out_free_2;
}
r = cpuhp_setup_state_nocalls(CPUHP_AP_KVM_STARTING, "kvm/cpu:starting",
kvm_starting_cpu, kvm_dying_cpu);
if (r)
goto out_free_2;
register_reboot_notifier(&kvm_reboot_notifier);
/* A kmem cache lets us meet the alignment requirements of fx_save. */
if (!vcpu_align)
vcpu_align = __alignof__(struct kvm_vcpu);
kvm_vcpu_cache =
kmem_cache_create_usercopy("kvm_vcpu", vcpu_size, vcpu_align,
SLAB_ACCOUNT,
offsetof(struct kvm_vcpu, arch),
sizeof_field(struct kvm_vcpu, arch),
NULL);
if (!kvm_vcpu_cache) {
r = -ENOMEM;
goto out_free_3;
}
r = kvm_async_pf_init();
if (r)
goto out_free;
kvm_chardev_ops.owner = module;
kvm_vm_fops.owner = module;
kvm_vcpu_fops.owner = module;
r = misc_register(&kvm_dev);
if (r) {
pr_err("kvm: misc device register failed\n");
goto out_unreg;
}
register_syscore_ops(&kvm_syscore_ops);
kvm_preempt_ops.sched_in = kvm_sched_in;
kvm_preempt_ops.sched_out = kvm_sched_out;
kvm_init_debug();
r = kvm_vfio_ops_init();
WARN_ON(r);
return 0;
out_unreg:
kvm_async_pf_deinit();
out_free:
kmem_cache_destroy(kvm_vcpu_cache);
out_free_3:
unregister_reboot_notifier(&kvm_reboot_notifier);
cpuhp_remove_state_nocalls(CPUHP_AP_KVM_STARTING);
out_free_2:
kvm_arch_hardware_unsetup();
out_free_1:
free_cpumask_var(cpus_hardware_enabled);
out_free_0:
kvm_irqfd_exit();
out_irqfd:
kvm_arch_exit();
out_fail:
return r;
}
EXPORT_SYMBOL_GPL(kvm_init);
|
可以看到，kvm_init() 会调用 misc_register() 函数来注册块设备 /dev/kvm。
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| static long kvm_dev_ioctl(struct file *filp,
unsigned int ioctl, unsigned long arg)
{
long r = -EINVAL;
switch (ioctl) {
case KVM_GET_API_VERSION:
if (arg)
goto out;
r = KVM_API_VERSION;
break;
case KVM_CREATE_VM:
r = kvm_dev_ioctl_create_vm(arg);
break;
case KVM_CHECK_EXTENSION:
r = kvm_vm_ioctl_check_extension_generic(NULL, arg);
break;
case KVM_GET_VCPU_MMAP_SIZE:
if (arg)
goto out;
r = PAGE_SIZE; /* struct kvm_run */
#ifdef CONFIG_X86
r += PAGE_SIZE; /* pio data page */
#endif
#ifdef CONFIG_KVM_MMIO
r += PAGE_SIZE; /* coalesced mmio ring page */
#endif
break;
case KVM_TRACE_ENABLE:
case KVM_TRACE_PAUSE:
case KVM_TRACE_DISABLE:
r = -EOPNOTSUPP;
break;
default:
return kvm_arch_dev_ioctl(filp, ioctl, arg);
}
out:
return r;
}
static struct file_operations kvm_chardev_ops = {
.unlocked_ioctl = kvm_dev_ioctl,
.llseek = noop_llseek,
KVM_COMPAT(kvm_dev_ioctl),
};
static struct miscdevice kvm_dev = {
KVM_MINOR,
"kvm",
&kvm_chardev_ops,
};
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创建虚拟机#
TODO