Keir Fraser wrote:

Is there any guest that actually cares about having EFER_NX really cleared?
Presumably the only way of detecting this would be reserved-bit page faults,
which no OS is likely to want to deliberately cause?

There's been some talk of NX'ing up Xen's data areas. In that case we
*would* need NX enabled always in host mode. Would it actually be worth
enabling/disabling on vmexit/vmentry?
SVM actually does automatically save/restore EFER on vmentry/vmexit. Could
we use VMX's MSR load/save support for the same effect? Would it be slow, or
interact badly with the existing support for switching EFER.LME?

AFAIK, this should be slow.
Thanks,
Gianluca
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