When working with KVM virtualization through virt-manager, many users encounter a frustrating behavior where the guest OS permanently captures mouse focus, requiring the Ctrl_L+Alt_L combination to release control. This occurs across multiple Linux distributions:

OS            virt-manager       libvirt       Focus Capture
-----------------------------------------------
Fedora 14     0.8.7-2            0.8.3-10      Yes
CentOS 5      0.6.1-16           0.8.2-25      Yes
CentOS 6      0.9.0-14           0.9.10-21     Yes

The issue stems from virt-manager's default input device configuration. The standard mouse emulation lacks proper focus release capabilities, particularly noticeable with Windows guests (though not exclusive to them).

Adding a virtual tablet device provides proper absolute pointer positioning and seamless focus transition:

<input type='tablet' bus='usb'/>

To implement this:

1. Shut down the guest VM
2. Edit the VM's XML configuration:

virsh edit vm_name

Add this section within the <devices> tag:

<input type='tablet' bus='usb'>
  <address type='usb' bus='0' port='1'/>
</input>

For users who prefer scripted solutions:

#!/bin/bash
# Add tablet device to all running VMs
for vm in $(virsh list --name --state-running); do
  virsh attach-device $vm <(cat <<EOF
<input type='tablet' bus='usb'>
  <address type='usb' bus='0' port='1'/>
</input>
EOF
) --config --live
done

After implementation, verify the input devices:

virsh dumpxml vm_name | grep -A5 '<input'

For enhanced functionality, consider combining with these QEMU options:

<graphics type='spice'>
  <clipboard copypaste='yes'/>
  <mouse mode='client'/>
</graphics>

The tablet input method adds minimal overhead (typically <1% CPU usage on modern systems). For environments with many simultaneous users, batch configuration is recommended:

for vm in $(virsh list --all --name); do
  virsh attach-device $vm tablet.xml --config
done

Where tablet.xml contains the input device configuration.

---

Working with Windows Server 2008 R2 (or other OSes) as KVM guests through virt-manager presents a common pain point: the forced mouse capture requiring Ctrl_L+Alt_L to release. This behavior persists across multiple distros:

OS            virt-manager       libvirt    
Fedora 14     0.8.7-2            0.8.3-10     
CentOS 5      0.6.1-16           0.8.2-25     
CentOS 6      0.9.0-14           0.9.10-21

The core issue stems from the default PS/2 mouse emulation in QEMU/KVM. When virt-manager initializes a VM, it typically creates input devices like:

<input type='mouse' bus='ps2'/>
<input type='keyboard' bus='ps2'/>

PS/2 devices require explicit focus capture/release because they can't handle absolute pointer positioning.

The most effective workaround involves adding a virtual tablet device to your VM configuration. This provides absolute pointer positioning similar to physical tablets.

For existing VMs, edit the XML configuration:

virsh edit vm_name
<!-- Add this under devices -->
<input type='tablet' bus='usb'/>

For new VMs using virt-manager GUI:

1. Open VM hardware details
2. Click "Add Hardware"
3. Select "Input" → "EvTouch USB Graphics Tablet"

If tablet devices aren't viable, consider these methods:

# 1. SPICE protocol with agent
<graphics type='spice'>
  <clipboard copypaste='yes'/>
</graphics>
<channel type='spicevmc'>
  <target type='virtio' name='com.redhat.spice.0'/>
</channel>

# 2. Xorg configuration tweak (host side)
Section "ServerFlags"
    Option "AutoAddDevices" "false"
    Option "AllowEmptyInput" "false"
EndSection

After implementing changes, verify with:

# Check active input devices
virsh dumpxml vm_name | grep -A5 "input device"

# Monitor input events
evtest /dev/input/eventX

Performance impact is typically negligible (<1% CPU overhead for tablet devices).

This behavior originates from early virtualization implementations where complete input device emulation was resource-prohibitive. Modern solutions leverage:

• VirtIO-input (kernel 3.8+)
• Multi-touch protocol extensions
• SPICE/QXL drivers