Crate kvm_ioctls[][src]

Expand description

A safe wrapper around the kernel’s KVM interface.

This crate offers safe wrappers for:

Platform support

  • x86_64
  • arm64 (experimental)

NOTE: The list of available ioctls is not extensive.

Example - Running a VM on x86_64

In this example we are creating a Virtual Machine (VM) with one vCPU. On the vCPU we are running machine specific code. This example is based on the LWN article on using the KVM API. The aarch64 example was modified accordingly.

To get code running on the vCPU we are going through the following steps:

  1. Instantiate KVM. This is used for running system specific ioctls.
  2. Use the KVM object to create a VM. The VM is used for running VM specific ioctls.
  3. Initialize the guest memory for the created VM. In this dummy example we are adding only one memory region and write the code in one memory page.
  4. Create a vCPU using the VM object. The vCPU is used for running vCPU specific ioctls.
  5. Setup architectural specific general purpose registers and special registers. For details about how and why these registers are set, please check the LWN article on which this example is built.
  6. Run the vCPU code in a loop and check the exit reasons.
extern crate kvm_ioctls;
extern crate kvm_bindings;

use kvm_ioctls::VcpuExit;
use kvm_ioctls::{Kvm, VcpuFd, VmFd};

fn main() {
    use std::io::Write;
    use std::ptr::null_mut;
    use std::slice;

    use kvm_bindings::kvm_userspace_memory_region;
    use kvm_bindings::KVM_MEM_LOG_DIRTY_PAGES;

    let mem_size = 0x4000;
    let guest_addr = 0x1000;
    let asm_code: &[u8];

    // Setting up architectural dependent values.
    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
        asm_code = &[
            0xba, 0xf8, 0x03, /* mov $0x3f8, %dx */
            0x00, 0xd8, /* add %bl, %al */
            0x04, b'0', /* add $'0', %al */
            0xee, /* out %al, %dx */
            0xec, /* in %dx, %al */
            0xc6, 0x06, 0x00, 0x80,
            0x00, /* movl $0, (0x8000); This generates a MMIO Write. */
            0x8a, 0x16, 0x00, 0x80, /* movl (0x8000), %dl; This generates a MMIO Read. */
            0xf4, /* hlt */
    #[cfg(target_arch = "aarch64")]
        asm_code = &[
            0x01, 0x00, 0x00, 0x10, /* adr x1, <this address> */
            0x22, 0x10, 0x00, 0xb9, /* str w2, [x1, #16]; write to this page */
            0x02, 0x00, 0x00, 0xb9, /* str w2, [x0]; This generates a MMIO Write. */
            0x00, 0x00, 0x00,
            0x14, /* b <this address>; shouldn't get here, but if so loop forever */

    // 1. Instantiate KVM.
    let kvm = Kvm::new().unwrap();

    // 2. Create a VM.
    let vm = kvm.create_vm().unwrap();

    // 3. Initialize Guest Memory.
    let load_addr: *mut u8 = unsafe {
            libc::PROT_READ | libc::PROT_WRITE,
            libc::MAP_ANONYMOUS | libc::MAP_SHARED | libc::MAP_NORESERVE,
        ) as *mut u8

    let slot = 0;
    // When initializing the guest memory slot specify the
    // `KVM_MEM_LOG_DIRTY_PAGES` to enable the dirty log.
    let mem_region = kvm_userspace_memory_region {
        guest_phys_addr: guest_addr,
        memory_size: mem_size as u64,
        userspace_addr: load_addr as u64,
        flags: KVM_MEM_LOG_DIRTY_PAGES,
    unsafe { vm.set_user_memory_region(mem_region).unwrap() };

    // Write the code in the guest memory. This will generate a dirty page.
    unsafe {
        let mut slice = slice::from_raw_parts_mut(load_addr, mem_size);

    // 4. Create one vCPU.
    let vcpu_fd = vm.create_vcpu(0).unwrap();

    // 5. Initialize general purpose and special registers.
    #[cfg(any(target_arch = "x86", target_arch = "x86_64"))]
        // x86_64 specific registry setup.
        let mut vcpu_sregs = vcpu_fd.get_sregs().unwrap();
        vcpu_sregs.cs.base = 0;
        vcpu_sregs.cs.selector = 0;

        let mut vcpu_regs = vcpu_fd.get_regs().unwrap(); = guest_addr;
        vcpu_regs.rax = 2;
        vcpu_regs.rbx = 3;
        vcpu_regs.rflags = 2;

    #[cfg(target_arch = "aarch64")]
        // aarch64 specific registry setup.
        let mut kvi = kvm_bindings::kvm_vcpu_init::default();
        vm.get_preferred_target(&mut kvi).unwrap();

        let core_reg_base: u64 = 0x6030_0000_0010_0000;
        let mmio_addr: u64 = guest_addr + mem_size as u64;
        vcpu_fd.set_one_reg(core_reg_base + 2 * 32, guest_addr); // set PC
        vcpu_fd.set_one_reg(core_reg_base + 2 * 0, mmio_addr); // set X0

    // 6. Run code on the vCPU.
    loop {
        match"run failed") {
            VcpuExit::IoIn(addr, data) => {
                    "Received an I/O in exit. Address: {:#x}. Data: {:#x}",
                    addr, data[0],
            VcpuExit::IoOut(addr, data) => {
                    "Received an I/O out exit. Address: {:#x}. Data: {:#x}",
                    addr, data[0],
            VcpuExit::MmioRead(addr, data) => {
                println!("Received an MMIO Read Request for the address {:#x}.", addr,);
            VcpuExit::MmioWrite(addr, data) => {
                println!("Received an MMIO Write Request to the address {:#x}.", addr,);
                // The code snippet dirties 1 page when it is loaded in memory
                let dirty_pages_bitmap = vm.get_dirty_log(slot, mem_size).unwrap();
                let dirty_pages = dirty_pages_bitmap
                    .map(|page| page.count_ones())
                    .fold(0, |dirty_page_count, i| dirty_page_count + i);
                assert_eq!(dirty_pages, 1);
                // Since on aarch64 there is not halt instruction,
                // we break immediately after the last known instruction
                // of the asm code example so that we avoid an infinite loop.
                #[cfg(target_arch = "aarch64")]
            VcpuExit::Hlt => {
            r => panic!("Unexpected exit reason: {:?}", r),


Wrapper over the file descriptor obtained when creating an emulated device in the kernel.

Wrapper over errno.

Wrapper over KVM system ioctls.

Safe wrapper over the kvm_run struct.

Helper structure for disabling datamatch.

Wrapper over KVM vCPU ioctls.

Wrapper over KVM VM ioctls.


Capabilities exposed by KVM.

An address either in programmable I/O space or in memory mapped I/O space.

Reasons for vCPU exits.