Here's the issue: The newer kernels have the retpoline Spectre mitigation. You're going to need to rebuild your nvidia.ko kernel module with a patched version of the stock distribution gcc.
Here is the bug: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1750937 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1754551 Title: Kernel 3.13.0-143 breaks multi-monitor support To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1754551/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs