Re: [Xen-devel] Weekly VMX status report. Xen: #18846 & Xen0: #749

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 13/12/2008 15:14, "Nakajima, Jun" <jun.nakajima@xxxxxxxxx> wrote:

>> Well, I vote for leaving EFER_NX always on then. It makes the code
>> simpler too. Anyone against this?
> 
> Agree. Modern VMX-capable processors can save/restore Guest/Host IA32_EFER in
> the VMCS at VM exit/entry time, and I don't expect additional overheads from
> that.
> 
> So the options are:
> 1. Enable that feature (does not help old processors, though), or
> 2. If the guest does not enable NX but the processor does, set/reset NX at VM
> entry/exit. We are already handling other bits (e.g. SCE).

I'm not clear what your position is from the above. I should point out that
we don't mess with EFER on vmentry/vmexit at all right now. We fix up
EFER.SCE and other bits on context switch, but not on every entry/exit.

I think you agree that we don't need to keep guest 'actual' EFER.NX in sync
with its 'shadow' EFER.NX?

 -- Keir



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