How to enable nested KVM in ubuntu 16.04

1. Check whether the nested KVM is enabled?
   cat /sys/module/kvm_intel/parameters/nested
   N
2. Upgrade the kernel to at least 3.18
   You can check you kernel version by #uname -a
3. Edit /etc/default/grub
   sudo vim /etc/default/grub
   append kvm-intel.nested=1 to the value of GRUB_CMDLINE_LINUX
4. #update-grub
5. Reboot your system.
   Reference
   http://www.linuxidc.com/Linux/2015-05/117026.htm
   http://www.rdoxenham.com/?p=275
   http://www.cnblogs.com/saptechnique/archive/2012/04/05/2433643.html