Right, but what x86 KVM setup is there in practice that doesnt present a mmu to its guest and hence keep its own track (shadow) of memory mappings?
replyShadow memory mappings are only needed when you do not have hardware virtualization or when doing nested virtualization.
replyFrom the page: "it can threaten the guest-host isolation of KVM/x86 hosts that accept untrusted guests and expose nested virtualization"
That is not to say that it is not a serious vulnerability though.