Hi Keir -

The attached patch (to 3.1.1-rc2) fixes a hypervisor crash that we're 
seeing when migrating a HVM guest from a machine that supports the NX 
bit to one that doesn't (e.g., because it's disabled in the BIOS).  It 
keeps the guest copy of EFER "as is", so the guest will see EFER_NX if 
it previously set it -- we just won't propagate this EFER bit to a 
non-NX-capable host.

Signed-off-by: David Lively <dlively@virtualiron.com>

I'm not sure whether this problem exists for AMDV, which has an EFER 
shadow in its vmcb.  Does their vmentry mechanism take care of this 
masking, or will we GPF when trying to propagate the shadow EFER_NX bit 
to the real one (when NX is disabled)?  I'll followup on this and submit 
a separate AMD patch if it's necessary.

Note this doesn't apply to unstable.  I'll do an unstable version 
if/when this one settles out.

Dave