[SOLVED] Linux 4.0 is in unstable, warning: nvidia-kernel-dkms won't build properly

So if you rely on the non-free nvidia drivers, don't uninstall your 3.16 kernel for a while. The module build fails due to:

error: implicit declaration of function ‘read_cr4’ [-Werror=implicit-function-declaration]      *cr4 = read_cr4();

leading to a dkpg error code. Searching for this shows nvidia already know about it, may even be fixed in newer driver versions, so we'll have to wait a bit for the fix to trickle into unstable.

There was an update to the driver, which now builds properly. Crisis averted!

I just updated to 4.0.0 nvidia driver 340.65-2 didn't build, but 340.76-2 does.