RE: [Xen-devel] EFER in HVM guests

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Nakajima, Jun
> Sent: 29 November 2006 16:35
> To: Jan Beulich; xen-devel@xxxxxxxxxxxxxxxxxxx; Keir Fraser
> Subject: RE: [Xen-devel] EFER in HVM guests
> 
> Jan Beulich wrote:
> >>>> Keir Fraser <keir@xxxxxxxxxxxxx> 29.11.06 14:09 >>>
> >> On 29/11/06 13:07, "Jan Beulich" <jbeulich@xxxxxxxxxx> wrote:
> >> 
> >>> Is it intentional that
> >>> - under SVM, 32-bit guests can freely set EFER.LME
> >>> - under VMX, 32-bit guests can't access EFER at all?
> >>> 
> >>> Thanks, Jan
> >> 
> >> I'm sure any differences are unintentional. There is 
> obviously scope
> >> for making much of the MSR and CPUID code non-vmx/svm specific.
> >> 
> >> I assume that this particular difference doesn't really matter?
> > 
> > I think it does - allowing a guest to enable EFER.LME when the
> > hypervisor is a 32-bit one is clearly a security problem: While I
> > haven't tried it, I would suspect the moment you load a context
> > with such an EFER the whole system's dead.
> > Not being able to access EFER is also a potential problem, as a
> > guest should be allowed to set EFER.NX (at least) - the CPUID
> > handling code specifically does not suppress this bit if the guest
> > is allowed to use PAE (which we agreed a few days ago should
> > be the default anyway).
> > 
> > Jan
> > 
> 
> I agree that we should allow 32-bit guests to set EFER.NX on the PAE
> Xen. We'll fix it. EFER.SCE should not be set on IA-32. 

Why not? If CPUID bits indicate that it's available, it can be used in
32- or 64-bit mode. 

--
Mats
> 
> Jun
> ---
> Intel Open Source Technology Center
> 
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> 



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