Do not allocate env->nested_state unless we later need to migrate the
nested virtualization state.
With this change, nested_state_needed() will return false if the
VMX flag is not included in the virtual machine. KVM_GET/SET_NESTED_STATE
is also disabled for SVM which is safer (we know that at least the NPT
root and paging mode have to be saved/loaded), and thus the corresponding
subsection can go away as well.
Inspired by a patch from Liran Alon.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
1e44f3ab71