Paolo Bonzini sent in the first round of KVM changes for the Linux 3.17 merge window. The MIPS/S390 architectures in particular have seen little changes this kernel development cycle while x86 has been a greater focus. Linux 3.17 KVM has nested VMX improvements, optimizations for old processors (up through Intel Nehalem CPUs), and various x86 emulator bug-fixes.
The PowerPC and ARM KVM changes will be submitted for Linux 3.17 in the days ahead. Linux virtualization users wanting to learn more about these x86 KVM changes can see the pull request with the full patch log that's been queued up of the KVM changes.