It happened several times to me that the installation of Tumbleweed just froze
at various stages of the installation when using virt-manager together with the
default QXL driver.

Symptoms: The UI will just freeze completely. Switching to other terminals is
not possible either.

However when starting an SSH daemon it's still possible to connect to the
machine.
When doing so no relevant output can be seen in dmesg. When attaching to the
Xorg process via strace nothing gets printed at all, getting the stack trace
(which won't change) of X shows the following:

1:install:~ # cat /proc/`pidof Xorg`/task/*/stack
[<0>] ttm_eu_reserve_buffers+0x1d9/0x2c0 [ttm]
[<0>] qxl_release_reserve_list+0x53/0x130 [qxl]
[<0>] qxl_cursor_atomic_update+0x17e/0x2a0 [qxl]
[<0>] drm_atomic_helper_commit_planes+0xae/0x210 [drm_kms_helper]
[<0>] drm_atomic_helper_commit_tail+0x26/0x60 [drm_kms_helper]
[<0>] commit_tail+0x58/0x70 [drm_kms_helper]
[<0>] drm_atomic_helper_commit+0x103/0x110 [drm_kms_helper]
[<0>] drm_atomic_helper_update_plane+0xf0/0x110 [drm_kms_helper]
[<0>] __setplane_internal+0x134/0x260 [drm]
[<0>] drm_mode_cursor_universal+0xdf/0x1c0 [drm]
[<0>] drm_mode_cursor_common+0x167/0x1d0 [drm]
[<0>] drm_ioctl_kernel+0x5b/0xb0 [drm]
[<0>] drm_ioctl+0x194/0x350 [drm]
[<0>] do_vfs_ioctl+0x90/0x5d0
[<0>] ksys_ioctl+0x60/0x90
[<0>] __x64_sys_ioctl+0x16/0x20
[<0>] do_syscall_64+0x60/0x110
[<0>] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[<0>] 0xffffffffffffffff