Comment 5 for bug 2009280

It does show in the docs, its just not pointed out very well,

https://www.qemu.org/docs/master/system/i386/hyperv.html

hv-evmcs

    The enlightenment is nested specific, it targets Hyper-V on KVM guests. When enabled, it provides Enlightened VMCS version 1 feature to the guest. The feature implements paravirtualized protocol between L0 (KVM) and L1 (Hyper-V) hypervisors making L2 exits to the hypervisor faster. *The feature is Intel-only.*

    Note: some virtualization features (e.g. Posted Interrupts) are disabled when hv-evmcs is enabled. It may make sense to measure your nested workload with and without the feature to find out if enabling it is beneficial.

    Requires: hv-vapic