I have an Ubuntu 13.10 and Windows 8 dual-boot working properly, and upgrading to Windows 8.1 breaks grub2 as expected. However, this time boot-repair was not able to bring grub back for me. My laptop jumps right into windows.
I double checked that Windows 8.1 re-enabled fast startup, so I've disabled it. And in my BIOS, UEIF is used for boot and secure-boot is disabled.
I have a 500GB GPT partition, in which, sda1 is the efi partion, sda2 is the /boot, sda3 is the / for ubuntu, and sda7 is the swap area. For Windows, sda4 is the msft reserve, sda5 is c://, and sda6 is Windows recovery. Those are (at least) my original setup.
Here's the boot info: http://paste.ubuntu.com/7051548/
I also tried mount my hard drive from a live ubuntu session, then re-install grub on /dev/sda, which didn't work either.
Is there any other thing I could try to bring my Ubuntu back?