Re: [Xen-devel] [PATCH] x86/cpuid: Tie SMAP to NX, for the shadow pagetable code

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.10.18 at 12:34, <andrew.cooper3@xxxxxxxxxx> wrote:
> NX support in the host is required for the shadow pagetable code to handle
> SMAP correctly for guests.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> CC: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
> CC: Tim Deegan <tim@xxxxxxx>
> 
> RFC because this is a little thorny.
> 
> Strictly speaking, it is "Xen uses NX in HVM guest context" as the
> prerequisite.  We could in principle allow guests to use NX without using it
> in Xen, but that sounds like unnecessary complication.  Also, we have no
> option to inhibit Xen from using NX if it finds it in hardware.
> 
> This dependency also doesn't need to occur for HAP guests.
> 
> In practice, all 64bit hardware (save the very first Intel 64bit CPUs)
> supports NX, and expressing the interlock like this is far easier than trying
> to account for it dynamically.

Fine with me nevertheless:
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan


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