The following commit fixes freezes in virtio device drivers when KVM is nested under VMWare Workstation/ESXi or Hyper-V. I've encountered problems running KVM inside VMWare since upgrading to Debian 9 (currently testing 4.9.88-1+deb9u1).

d391f1207067268261add0485f0f34503539c5b0

The same issue affects 4.4.y as well. A git-bisect within my environment stopped at e9ea5069d9e569c32ab913c39467df32e056b3a7, where the KVM capability was added that QEMU checks before enabling fast mmio.

Thanks, Mike