Host mouse pointer not aligned with guest mouse pointer in Qemu VNC

mouseqemuvirtual machinevnc

When I run Tiny Core Linux in a Qemu virtual machine, the guest mouse pointer is severely misaligned with the host mouse pointer. In the screenshot below, the guest mouse pointer is the one in the image. The red dot marks the location of the host mouse pointer.

I create the Qemu disk image with this command:

qemu-img create disk.img 500M -f qcow2

and launch the virtual machine with this command:

qemu-system-x86_64 -m 1024 -boot d -enable-kvm -smp 3 -net nic -net user -hda disk.img -cdrom TinyCore-current.iso

That starts a VNC session running on ::1:5900, which I access with Remmina by specifying localhost:5900 as the server.

I'm using Remmina 1.3.3, Qemu 1.3.1, and Debian 10 ("Buster"). How do I correctly align these mouse pointers? The guest machine is difficult to use when they're misaligned.

EDIT: This issue also shows up in TigerVNC Viewer 64-bit v1.9.0, so it seems like it isn't a Remmina problem, but rather a Qemu problem.

EDIT: To clarify, in my version of qemu , I get the error qemu-system-x86_64: -usbdevice tablet: '-usbdevice' is deprecated, please use '-device usb-...' instead, but when I use the -device usb-tablet option I get the error qemu-system-x86_64: -device usb-tablet: No 'usb-bus' bus found for device 'usb-tablet'. I've seen this suggestion on this site and elsewhere, but it doesn't seem like it's a proper, compatible solution to my problem.

Best Answer

it's because generic mouse hardwares only send movement events, ie. relative positioning device. so when qemu gets the absolute mouse position on its vnc interface, it can not do the same by the emulated mouse, it only sends the relative movement, because this is what generic hw mice do.

however you can emulate absolute positioning device by -usbdevice tablet option. if you're lucky the guest OS also supports it.

Related Solutions

Qemu 2.0 Windows guest – mouse stops working (vnc) when using usb-passthrough

I finally found a fix for this bug/problem! It is in fact a bug, but I don't know whether it is a Windows bug or a Qemu/VNC-bug. After connecting a massive storage device to the Windows 8.1 guest, the mouse stops working because it goes into a sleep-state.

This bug can be fixed by going to WIN + X, Control Panel, Devices and Printers. There you can see the QEMU USB Tablet which is a tablet/mouse device used for the VNC-mouse to work on the guest. Right click it and select Properties. Next click on the tab Hardware. Normally you should see two devices (based on what hardware you assigned to the guest), HID-compliant mouse and USB Input Device.

Now select the USB Input Device and click Properties at the bottom. This will open a new window with the device's properties. Next click on Change settings (you'll need Admin.-powers for this) and go to the Power Management tab on the newly opened window. There you should see an option ticked with the following explanation: Allow the computer to turn off this device to save power.

Unchecking that option and pressing OK solves the problem. This whole route can be done with keyboard-only (as the keyboard still works). Press ENTER to open things, use TAB to move to different menus and press SPACE to simulate a single mouse-click (for unchecking the checkbox).

I still can't find any related topics of people having the same issues as I did, but it is a bug and should be fixed. I have no idea if it is Windows or Qemu related and I hope that the Qemu-team can further inspect this.

Qemu USB passthrough (windows guest)

I finally got help on the other forum. The issue seems to be with the USB bus implementation in I440FX chipset that is emulated by qemu by default (details here). The workaround is emulating the ICH9 chipset instead. This is done by adding -M q35 parameter. I also changed the way the USB devices are specified and the final command line looks like this:

qemu-system-x86_64 \
    -enable-kvm \
    -M q35 \
    -m 2G \
    -usb -usbdevice host:16b2:1001 \
    -usb -usbdevice host:0529:0001 \
    -usbdevice tablet \
    -net nic \
    -net bridge,br=br0 \
    -vga qxl \
    -spice port=5930,disable-ticketing \
    -device virtio-serial-pci \
    -device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 \
    -chardev spicevmc,id=spicechannel0,name=vdagent \
    -drive file=/mnt/data/win-patch.img,if=virtio

Everything works perfectly now.

Update for 2019: the usb-device option was deprecated; you can achieve the same by replacing it with -usb -device and specifying product and vendor id in hexadecimal numbers, likewise:

qemu-system-x86_64 \
    -enable-kvm \
    -M q35 \
    -m 2G \
    -usb -device usb-host:productid=0x16b2,vendorid=0x1001 \
    -usb -device usb-host:productid=0x0529,vendorid=0x0001 \
    -usbdevice tablet \
    -net nic \
    -net bridge,br=br0 \
    -vga qxl \
    -spice port=5930,disable-ticketing \
    -device virtio-serial-pci \
    -device virtserialport,chardev=spicechannel0,name=com.redhat.spice.0 \
    -chardev spicevmc,id=spicechannel0,name=vdagent \
    -drive file=/mnt/data/win-patch.img,if=virtio

reference: https://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/usb2.txt;hb=HEAD

Best Answer

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