In the environment I managed(vSphere 6.0), vMotion is working fine among hosts with Broadwell CPU & Skylake CPU wihtou EVC, can anyone help to explain why? Not new features in Skylake CPU will affect Broadwell CPU processing?
The highest virtual hardware version that ESXi 6.0 supports is version 11. Version 11 exposes Haswell instructions such as INVPCID, AVX2. If a VM has version 10 even with ESXi 6.0, the Haswell instructions become hidden. The version acts as a natural mask.
The likely reason it works for ESXi 6.0 without EVC for Broadwell and Skylake CPUs is because ESXi cannot take advantage of Broadwell and Skylake CPUs features. You do risk of having the guest OS or applications within the VM suddenly fail if it goes from Skylake to Broadwell when it makes use of features/instructions not available in Broadwell. Example: Skylake Xeons would have AVX512 and Broadwell Xeons won't. Some features of CPUs do not require hypervisor initialisation and the guest OS will be able to access it through VT-x.