No UMS support in radeon module

After upgrading my lubuntu to "Ubuntu 17.10 - 4.13.0-16-generic Kernel" I get a black screen after boot, probably for the following problem:

dmesg | egrep 'drm|radeon'

Result:

[ 2.493943] [drm] VGACON disable radeon kernel modesetting.
[ 2.494058] [drm:radeon_init [radeon]] *ERROR* No UMS support in radeon module!
[ 18.891836] [drm] VGACON disable radeon kernel modesetting.
[ 18.891896] [drm:radeon_init [radeon]] *ERROR* No UMS support in radeon module!
[ 27.041720] [drm] VGACON disable radeon kernel modesetting.
[ 27.041818] [drm:radeon_init [radeon]] *ERROR* No UMS support in radeon module!

If I run the following command:

lspci -nn | grep VGA

I get the following result:
VGA compatible controller [0300]: Advanced Micro Devices, Inc. [AMD/ATI] RV370/M22 [Mobility Radeon X300] [1002:5460]

NB: my system actually runs only in recovery mode

Any suggestions?