Package: qemu-system-gui Version: 1:3.1+dfsg-2 After upgrading from Debian Stretch to Buster, thus changing the qemu version on host, "-display gtk" has to be used instead of "sdl" as the later is not available with Buster any more.
Since that switch the mouse behaviour changed, making guest machines (also Debian Buster) very hard to use. I do not know the old Stretch behaviour with "gtk" interface as I never used it. Reproduce: Run a qemu instance with "-vga virtio" and "-display gtk". Maybe the window manager is relevant also, using fvwm2 with an EdgeScroll configuration on host/guest shows the problematic behaviour. There are no specific guest additions installed in the guest nor acceleration in place. Following options exist for still using the mouse/vm: a) Using "Grab input" and "fullscreen", the mouse position is correct, but one cannot see any guest mouse pointer. Only changes in hilighting or menu popups (when clicking) indicate the current mouse position. b) Using "fullscreen" and then "grab input" does show the mouse pointer but mouse position near the screen edge is not submitted to the guest, those events seem to be consumed on host before that. Thus those mouse positions cannot be reached in the guest window. c) Not using fullscreen: fonts are harder to read due to scaling on quite small mobile display (that's why the fullscreen preference to avoid pixel-rot). The mouse pointer is shown and edge detection would work theoretically, but it usually should happen in some undistinguishable area where the guest-screen-background color changes to the same color gtk-window-background, thus it is very hard to hit it with the pointer. So essentially one can decide beween working mouse cursor display or working mouse pointer position, but you cannot have both. The current workaround is to switch between a) and b) requiring 8 multi-key strokes and one mouse gesture instead of having just to move the mouse pointer to the edge of the screen (old behaviour with sdl).
