No evdev mouse passthrough with virtio-vga or kvm

This bug has been copied automatically from: https://bugs.launchpad.net/qemu/+bug/1818398
Reported by 'gatestallman' on 2019-03-03 :

Hi,

Using qemu version 3.1.0-1 on a host with the latest Archlinux 64-bit
distribution, and running the same OS as guest, the mouse doesn't work
when using both evdev passthrough and virtio-vga, or when using both evdev
passthrough and kvm.

The following command line runs a machine that does not receive any mouse
event:
qemu-system-x86_64 -machine type=q35,accel=kvm -cpu host -accel kvm -boot
order=dc,menu=on -m size=2048 -net nic -device virtio-vga -device intel-
hda -name Linux -drive file=/mnt/data/nobody/linux/arch.img,if=virtio
-display sdl,gl=on -full-screen -net user -D /dev/null -rtc
base=utc,clock=host,driftfix=slew -nodefaults -object input-
linux,id=kbd1,evdev=/dev/input/event6,grab_all=on,repeat=on -object input-
linux,id=mouse1,evdev=/dev/input/event7

But with this command line, removing virtio-vga and kvm, the mouse works
as expected:
qemu-system-x86_64 -machine type=q35 -boot order=dc,menu=on -m size=2048
-net nic -device cirrus-vga -device intel-hda -name Linux -drive
file=/mnt/data/nobody/linux/arch.img,if=virtio -display sdl,gl=on -full-
screen -net user -D /dev/null -rtc base=utc,clock=host,driftfix=slew
-nodefaults -object input-
linux,id=kbd1,evdev=/dev/input/event6,grab_all=on,repeat=on -object input-
linux,id=mouse1,evdev=/dev/input/event7

Note: Passing a keyboard by evdev in the same way always works, the
problem is mouse specific.

Thanks in advance for the analysis,
gatestallman