qemu中KVM硬件虚拟化的初始化分析

1.传入-enable-kvm参数，启用KVM硬件虚拟化支持：
在文件qemu-options.hx中，有对参数-enable-kvm的定义，如下：
DEF("enable-kvm", 0, QEMU_OPTION_enable_kvm, \
    "-enable-kvm     enable KVM full virtualization support\n", QEMU_ARCH_ALL)
STEXI
@item -enable-kvm
@findex -enable-kvm
Enable KVM full virtualization support. This option is only available
if KVM support is enabled when compiling.
ETEXI


2.main函数中对应的参数解析


int main(int argc, char **argv, char **envp)
{
    /* second pass of option parsing */
    optind = 1;
    for(;;) {
    ......
        case QEMU_OPTION_enable_kvm:
        olist = qemu_find_opts("machine");
        qemu_opts_parse(olist, "accel=kvm", 0);
        break;
    ......
    ｝
    ......
    os_daemonize();
    ......
    configure_accelerator(machine);
    ......
}




(gdb) p *machine
$46 = {name = 0x555555a17666 "pc-i440fx-2.0", alias = 0x555555a17674 "pc", 
  desc = 0x555555a175d8 "Standard PC (i440FX + PIIX, 1996)", init = 0x5555558c2e2c , reset = 0, 
  hot_add_cpu = 0x5555558c1061 , kvm_type = 0, block_default_type = IF_IDE, max_cpus = 255, no_serial = 0, 
  no_parallel = 0, use_virtcon = 0, use_sclp = 0, no_floppy = 0, no_cdrom = 0, no_sdcard = 0, is_default = 1, 
  default_machine_opts = 0x555555a17677 "firmware=bios-256k.bin", default_boot_order = 0x555555a1768e "cad", compat_props = 0x0, 
  next = 0x0, hw_version = 0x0}


//qemu支持4种方式执行：tcg、xen、kvm、qtest
static struct {
    const char *opt_name;
    const char *name;
    int (*available)(void);
    int (*init)(QEMUMachine *);
    bool *allowed;
} accel_list[] = {
    { "tcg", "tcg", tcg_available, tcg_init, &tcg_allowed },
    { "xen", "Xen", xen_available, xen_init, &xen_allowed },
    { "kvm", "KVM", kvm_available, kvm_init, &kvm_allowed },
    { "qtest", "QTest", qtest_available, qtest_init_accel, &qtest_allowed },
};


//解析参数，并初始化相关模块
static int configure_accelerator(QEMUMachine *machine)
{
    const char *p;
    char buf[10];
    int i, ret;
    bool accel_initialised = false;
    bool init_failed = false;


    //在没有带-enable-kvm参数时，默认采用软件仿真的tcg
    p = qemu_opt_get(qemu_get_machine_opts(), "accel");
    if (p == NULL) {
        /* Use the default "accelerator", tcg */
        p = "tcg";
    }


    while (!accel_initialised && *p != '\0') {
        if (*p == ':') {
            p++;
        }
        p = get_opt_name(buf, sizeof (buf), p, ':');
        for (i = 0; i < ARRAY_SIZE(accel_list); i++) {
            if (strcmp(accel_list[i].opt_name, buf) == 0) {
                if (!accel_list[i].available()) {
                    printf("%s not supported for this target\n",
                           accel_list[i].name);
                    continue;
                }
                *(accel_list[i].allowed) = true;
                ret = accel_list[i].init(machine);
                if (ret < 0) {
                    init_failed = true;
                    fprintf(stderr, "failed to initialize %s: %s\n",
                            accel_list[i].name,
                            strerror(-ret));
                    *(accel_list[i].allowed) = false;
                } else {
                    accel_initialised = true;
                }
                break;
            }
        }
        if (i == ARRAY_SIZE(accel_list)) {
            fprintf(stderr, "\"%s\" accelerator does not exist.\n", buf);
        }
    }


    if (!accel_initialised) {
        if (!init_failed) {
            fprintf(stderr, "No accelerator found!\n");
        }
        exit(1);
    }


    if (init_failed) {
        fprintf(stderr, "Back to %s accelerator.\n", accel_list[i].name);
    }


    return !accel_initialised;
}




3.kvm_init


int kvm_init(QEMUMachine *machine)
{
......


s->fd = qemu_open("/dev/kvm", O_RDWR);
    if (s->fd == -1) {
        fprintf(stderr, "Could not access KVM kernel module: %m\n");
        ret = -errno;
        goto err;
    }
    //匹配kvm内核模块的版本，版本太旧或者太新都会不支持
    ret = kvm_ioctl(s, KVM_GET_API_VERSION, 0);
    if (ret < KVM_API_VERSION) {
        if (ret > 0) {
            ret = -EINVAL;
        }
        fprintf(stderr, "kvm version too old\n");
        goto err;
    }


    if (ret > KVM_API_VERSION) {
        ret = -EINVAL;
        fprintf(stderr, "kvm version not supported\n");
        goto err;
    }
    ......
    /* check the vcpu limits */
    soft_vcpus_limit = kvm_recommended_vcpus(s); //获取kvm内核推荐使用的vcpu个数
    hard_vcpus_limit = kvm_max_vcpus(s); //获取kvm内核最多可用的vcpu个数
    ......
    do {
        ret = kvm_ioctl(s, KVM_CREATE_VM, type); //创建一个VM
    } while (ret == -EINTR);


    ......
    ret = kvm_arch_init(s);
    if (ret < 0) {
        goto err;
    }


    ret = kvm_irqchip_create(s);
    if (ret < 0) {
        goto err;
    }


    kvm_state = s;
    memory_listener_register(&kvm_memory_listener, &address_space_memory);
    memory_listener_register(&kvm_io_listener, &address_space_io);


    s->many_ioeventfds = kvm_check_many_ioeventfds();


    cpu_interrupt_handler = kvm_handle_interrupt;


    return 0;
    ......
}