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Looking Glass B7 with IVSHMEM

The action in this article has been conducted under the following conditions:

Property Value
Date September 2026
Kernel 6.8.0-139-generic
Distribution Linux Mint 22.3
QEMU 8.2.2
libvirt 10.0.0
Looking Glass B7 (27fe47cb, 2025-03-06)
kvmfr 0.0.9 (DKMS)

Official docs: libvirt/QEMU, kvmfr, Windows host, Linux client. Related: Windows 11 Gaming VM with GPU pass-thru.

Problem

A VFIO Windows guest paints on the passed-through GPU. The host cannot see that framebuffer through Spice or virt-manager. Looking Glass copies frames over IVSHMEM so the Linux desktop can display the guest with low latency.

The Ubuntu / Mint looking-glass-client package is B6. The Windows host installer and the Linux client must be the same stable version. B7 is current stable.

Do not run two domains against the same IVSHMEM file (or the same GPU) at once.

Rust virtiofsd 1.10 (Ubuntu / Mint 22) dies with Illegal seek / vhost_set_mem_table failed if the domain also maps /dev/kvmfr0. That char device is not seekable, so the daemon exits and the guest share disappears. Use standard /dev/shm IVSHMEM on any guest that also has virtiofs. Keep kvmfr for domains that do not use virtiofs.

Host: shared memory

A 32 MiB file is enough for 1080p SDR. Use 64 MiB for 1440p SDR.

# /etc/tmpfiles.d/10-looking-glass.conf
f /dev/shm/looking-glass 0660 <user> kvm -

sudo systemd-tmpfiles --create /etc/tmpfiles.d/10-looking-glass.conf

If AppArmor is enforcing, allow /dev/shm/looking-glass rw, in /etc/apparmor.d/local/abstractions/libvirt-qemu.

Domain XML

Keep Spice for input and clipboard, drop the emulated QXL head (passthrough GPU is the only display), drop the USB tablet, and add virtio keyboard/mouse. Use libvirt <shmem>, not a qemu:commandline kvmfr backend.

<domain type="kvm">
  <!-- … -->
  <channel type="spicevmc">
    <target type="virtio" name="com.redhat.spice.0"/>
  </channel>
  <input type="mouse" bus="ps2"/>
  <input type="keyboard" bus="ps2"/>
  <input type="mouse" bus="virtio"/>
  <input type="keyboard" bus="virtio"/>
  <graphics type="spice" autoport="yes">
    <listen type="address"/>
    <image compression="off"/>
    <gl enable="no"/>
  </graphics>
  <sound model="ich9">
    <audio id="1"/>
  </sound>
  <audio id="1" type="spice"/>
  <video>
    <model type="none"/>
  </video>
  <shmem name="looking-glass">
    <model type="ivshmem-plain"/>
    <size unit="M">32</size>
  </shmem>
  <memballoon model="none"/>
</domain>

virsh define the inactive XML. virt-manager’s console will be blank after video none; that is expected.

Linux client (B7 from source)

Download the stable source artifact from looking-glass.io/downloads, not apt install looking-glass-client.

mkdir -p client/build
cmake -S client -B client/build -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX="$HOME/.local"
cmake --build client/build -j"$(nproc)"
cmake --install client/build
looking-glass-client --help   # banner: Looking Glass (B7)

B7 defaults app:shmFile to /dev/kvmfr0. Point it at the shm file instead. The client does not save the last window position; win:position is only the startup coordinate (center or <left>x<top>).

# ~/.config/looking-glass/client.ini
[app]
shmFile=/dev/shm/looking-glass

[win]
size=1920x1080
position=2112x180
autoResize=no
fullScreen=no
maximize=no
borderless=no

[input]
grabKeyboardOnFocus=yes
ignoreWindowsKeys=no

win:position is <left>x<top> in the combined desktop. 0x0 plus 1920x1080 fills a 1080p output and the window manager treats that as fullscreen. The values above park a 1080p window on a 2560×1440 display at +1920+0. win:autoResize=yes follows the guest framebuffer, not a fixed 1080p.

input:grabKeyboardOnFocus sends host combos such as Win+R into the guest as soon as the Looking Glass window has keyboard focus (no Scroll Lock). ignoreWindowsKeys=no is the default and must stay off. Hover alone is not enough on a click-to-focus desktop; enable sloppy/mouse focus in the window manager if the pointer entering the window should grab keys. Leave input:captureOnFocus off unless the mouse should lock into the window on focus.

Windows host (B7)

  1. Start the domain so the new IVSHMEM device is present.
  2. Copy looking-glass-host-setup.exe from the B7 Windows Host artifact into the guest (virtiofs or ISO).
  3. Run the installer as Administrator. Since B6 the installer ships the IVSHMEM driver.
  4. Install the virtio input driver (vioinput) from virtio-win if Device Manager shows unknown keyboard/mouse devices.
  5. Optional clipboard: Spice guest tools, with the com.redhat.spice.0 channel above.

Host log on failure: %ProgramData%\Looking Glass (host)\looking-glass-host.txt.

Guest needs a display sink (AMD)

Post-GCN AMD GPUs power down the display block when nothing is plugged in. DXGI then has no desktop to capture, so the Linux client stays on the splash / blank even though both Looking Glass processes are running.

video none plus GPU passthrough does not count as a monitor. Attach a real display to the guest GPU, or a DisplayPort/HDMI dummy plug. After the sink appears, restart the Looking Glass host service (or reboot the guest) and reopen the client.

Stable B7 has no Indirect Display Driver. Bleeding-edge builds ship a Windows IDD if you want a virtual sink later.

Run

looking-glass-client

If the client says it is waiting for the host, the Windows service is not running or IVSHMEM is missing. If both ends are running but the picture is still empty, check the guest GPU has a sink. If the picture is cropped at the bottom, the IVSHMEM size is too small for that resolution.

If virtiofs dies with Illegal seek / vhost_set_mem_table failed, the domain is still mapping /dev/kvmfr0. Remove the kvmfr qemu:commandline block.