x86/shadow: suppress "fast fault path" optimization when running virtualized

x86/shadow: suppress "fast fault path" optimization when running virtualized

We can't make correctness of our own behavior dependent upon a
hypervisor underneath us correctly telling us the true physical address
with hardware uses. Without knowing this, we can't be certain reserved
bit faults can actually be observed. Therefore, besides evaluating the
number of address bits when deciding whether to use the optimization,
also check whether we're running virtualized ourselves. (Note that since
we may get migrated when running virtualized, the number of address bits
may also change.)

Requested-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Tim Deegan <tim@xen.org>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>