Re: [Xen-devel] [PATCH v4 11/26] xen/x86: Improvements to in-hypervisor cpuid sanity checks

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 23/03/16 16:36, Andrew Cooper wrote:
> Currently, {pv,hvm}_cpuid() has a large quantity of essentially-static logic
> for modifying the features visible to a guest.  A lot of this can be subsumed
> by {pv,hvm}_featuremask, which identify the features available on this
> hardware which could be given to a PV or HVM guest.
>
> This is a step in the direction of full per-domain cpuid policies, but lots
> more development is needed for that.  As a result, the static checks are
> simplified, but the dynamic checks need to remain for now.
>
> As a side effect, some of the logic for special features can be improved.
> OSXSAVE and OSPKE will be automatically cleared because of being absent in the
> featuremask.  This allows the fast-forward logic to be more simple.
>
> In addition, there are some corrections to the existing logic:
>
>  * Hiding PSE36 out of PAE mode is architecturally wrong.  It turns out that
>    it was a bugfix for running HyperV under Xen, which wanted to see PSE36
>    even after choosing to use PAE paging.  PSE36 is not supported by shadow
>    paging, so is hidden from non-HAP guests, but is still visible for HAP
>    guests.

This paragraph is slightly stale.

As one further sentence,  "It is also leaked into non-HAP guests when
the guest is running in PAE mode, to placate HyperV."

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel