recovering GRUB bootloader on windows/ubuntu dual boot machine

I installed both windows and ubuntu on my laptop. It's easy to dual boot because I installed ubuntu after windows. But for some reasons, I have to reinstall windows.
And after windows is installed, dual boot no longer work because windows installer overwrited the mbr. I didn't want to install ubuntu again, and luckily, I found this: Dual Boot Ubuntu and Windows.
In short, we can fix the grub with following steps:

1. Boot with ubuntu live cd
2. Mount the ubuntu installation file system
3. Reinstall grub with "grub-setup -d ubuntu_installation_path/boot/grub" command