The PowerPC version of KVM for Linux virtualization allows the HV and emulation versions of the Kernel-based Virtual Machine to now co-exist in the same Linux kernel image. There's also other assorted PowerPC virtualization improvements.
For more common x86 virtualizationm, there's improvements to nested virtualization and various bug-fixes.
ARM virtualization is still in its infancy since hardware-assisted virtualization became possible with the Cortex-A15 SoCs. On the KVM ARM front, there's now transparent huge-page support, improved over-commit handling, and support for big endian guests.
The last KVM feature advertised for the Linux 3.13 kernel is a nw interface to connect KVM with VFIO. This change helps when passing devices to guests that use NoSnoop PCI translations so drivers inside the guest can use WBINVD instructions -- this along with user-space work allows for some NVIDIA graphics cards to work on Windows guests. As covered on Phoronix a few days ago, there continues to be KVM and VFIO work for passing graphics cards to guest VMs so that they can use the hardware directly from a real driver on the guest operating system.
More of the KVM improvement details for the Linux 3.13 merge window can be found from the pull request issued by Paolo Bonzini.