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tiny_qemu模拟qemu虚拟化原理

news 2025/8/15 13:19:31

一、模仿一个x86平台虚机

cpu虚拟化原理来源于Linux虚拟化KVM-Qemu分析（四）之CPU虚拟化（2）

笔者就实现了下相关操作。看汇编是在x86平台下操作的，其中两个文件分别是

1.tiny_kernel.S

start:
/* Hello */
mov     $0x48, %al
outb    %al, $0xf1
mov     $0x65, %al
outb    %al, $0xf1
mov     $0x6c, %al
outb    %al, $0xf1
mov     $0x6c, %al
outb    %al, $0xf1
mov     $0x6f, %al
outb    %al, $0xf1
mov     $0x2c, %al
outb    %al, $0xf1/* world */
mov     $0x77, %al
outb    %al, $0xf1
mov     $0x6f, %al
outb    %al, $0xf1
mov     $0x72, %al
outb    %al, $0xf1
mov     $0x6c, %al
outb    %al, $0xf1
mov     $0x64, %al
outb    %al, $0xf1mov     $0x0a, %al
outb    %al, $0xf1hlt

2.tiny_qemu.c （这个用例程序写得很经典）

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/kvm.h>
#include <sys/mman.h>#define KVM_DEV     "/dev/kvm"
#define TINY_KERNEL_FILE    "./tiny_kernel.bin"
#define PAGE_SIZE  0x1000int main(void)
{int kvm_fd;int vm_fd;int vcpu_fd;int tiny_kernel_fd;int ret;int mmap_size;struct kvm_sregs sregs;struct kvm_regs regs;struct kvm_userspace_memory_region mem;struct kvm_run *kvm_run;void *userspace_addr;/* open kvm device */kvm_fd = open(KVM_DEV, O_RDWR);assert(kvm_fd > 0);/* create VM */vm_fd = ioctl(kvm_fd, KVM_CREATE_VM, 0);assert(vm_fd >= 0);/* create VCPU */vcpu_fd = ioctl(vm_fd, KVM_CREATE_VCPU, 0);assert(vcpu_fd >= 0);/* open tiny_kernel binary file */tiny_kernel_fd = open(TINY_KERNEL_FILE, O_RDONLY);assert(tiny_kernel_fd > 0);/* map 4K into memory */userspace_addr = mmap(NULL, PAGE_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANONYMOUS, -1, 0);assert(userspace_addr > 0);/* read tiny_kernel binary into the memory */ret = read(tiny_kernel_fd, userspace_addr, PAGE_SIZE);assert(ret >= 0);/* set user memory region */mem.slot = 0;mem.flags = 0;mem.guest_phys_addr = 0;mem.memory_size = PAGE_SIZE;mem.userspace_addr = (unsigned long)userspace_addr;ret = ioctl(vm_fd, KVM_SET_USER_MEMORY_REGION, &mem);assert(ret >= 0);/* get kvm_run */mmap_size = ioctl(kvm_fd, KVM_GET_VCPU_MMAP_SIZE, NULL);assert(mmap_size >= 0);kvm_run = (struct kvm_run *)mmap(NULL, mmap_size, PROT_READ | PROT_WRITE, MAP_SHARED, vcpu_fd, 0);assert(kvm_run >= 0);/* set cpu registers */ret = ioctl(vcpu_fd, KVM_GET_SREGS, &sregs);assert(ret >= 0);sregs.cs.base = 0;sregs.cs.selector = 0;ret = ioctl(vcpu_fd, KVM_SET_SREGS, &sregs);memset(&regs, 0, sizeof(struct kvm_regs));regs.rip = 0;ret = ioctl(vcpu_fd, KVM_SET_REGS, &regs);assert(ret >= 0);/* vcpu run */while (1) {ret = ioctl(vcpu_fd, KVM_RUN, NULL);assert(ret >= 0);switch(kvm_run->exit_reason) {case KVM_EXIT_HLT:printf("----KVM EXIT HLT----\n");close(kvm_fd);close(tiny_kernel_fd);return 0;case KVM_EXIT_IO:putchar(*(((char *)kvm_run) + kvm_run->io.data_offset));break;default:printf("Unknow exit reason: %d\n", kvm_run->exit_reason);break;}}return 0;
}

程序原理很简单，就是模仿kvm-qemu那一套。