Re: [Xen-devel] [PATCH] HVM x86_32 PAE guest support on 64-bit Xen

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 19 Feb 2006, at 02:39, Nakajima, Jun wrote:

> The VMX does not save/restore NXE (bit 11) and SCE (bit 0), and they 
> are
> always set in Xen (on machines where VMX is available). So it's 
> possible
> that those bits are still effectively on in the guest even after the
> guest attempted to clear them (and we ignore such writes). I don't 
> think
> bad things can happen practically. We need to check carefully if we
> might expose security holes there.
Isn't SYSENTER effectively disabled if SYSENTER_CS == 0? Presumably the 
guest wouldn't touch that MSR unless it intends to set SCE.
And NXE should be okay so long as no OS has been borrowing the m.s.b. 
of PTEs in PAE36. Which seems unlikely.
 -- Keir


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