A small update: the behavior is caused by setting unrestricted_guest feature to N, I had this feature disabled everywhere from approx. three years ago when its enablement was one of suspects of the host crashes with contemporary then KVM module. Also nVMX is likely to not work at all and produce the same traces as in https://lkml.org/lkml/2014/7/17/12 without unrestricted_guest=1. I think this fact actually explaining all real mode weirdness we`ve seen before and this should be probably ended either by putting appropriate bits in a README or module information or making strict dependency between apicv/unrestricted_guest+nested/unrestricted_guest or fixing the issue at its root if this is possible or appropriate solution. Thanks everyone for keeping up with ideas through this thread!
