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

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 12/12/2008 23:30, "Gianluca Guida" <gianluca.guida@xxxxxxxxxxxxx> wrote:

> 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?
> 
> Yes, no OS we've actually experienced at the moment rely on reserved bit
> faults (with the most notable exception of Tim's fast path for MMIO and
> non present pages in Xen's shadow entries).
> I am sure about this for a very simple reason: -- some kind of secret I
> would like to share with you and xen-devel -- shadow code doesn't check
> at all for reserved bits when propagating changes from guest to shadows,
> so we never propagate reserved bit faults to guests. [working on this]

Well, I vote for leaving EFER_NX always on then. It makes the code simpler
too. Anyone against this?

 -- Keir



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