Initial support for the 64-bit ARM architecture was merged in Linux 3.7 and since then with each succeeding update we have seen support improvements. It's still not expected to see any ARM64 devices on the market until next year, but the Linux support has been materializing quick due to the large role Linux plays in the ARM world.
New to the Linux 3.10 kernel for ARM's 64-bit architecture is support for the 64-bit version of their Versatile Express SoC, basic multi-cluster support, simple early printk support, optimized kernel functions, and automatic initialization of the irqchip and clocks via the DeviceTree.
The Versatile Express continues to be ARM's development system for flexible and modular prototyping by ARM licensees and other vendors. Versatile Express is also what QEMU has been targeting for emulating in the ARM world.
The 64-bit ARM pull request for Linux 3.10 has been merged to mainline.
Aside from the kernel support, the Linux and open-source support for other components relating to AArch64 has also been coming up quite well, as detailed in other articles.