Re: [RFC PATCH 17/35] Segment register changes for Xen

Chris Wright
2006-05-18T21:23:10Z

* Zachary Amsden (zach@vmware.com) wrote:
> Chris Wright wrote:
> >1. We clear FS/GS before changing TLS entries and switching LDT, as
> >otherwise the hypervisor will fail to restore thread-local values on
> >return to the guest kernel and we take a slow exception path.
>
> >@@ -647,6 +647,8 @@ struct task_struct fastcall * __switch_t
> > */
> > savesegment(fs, prev->fs);
> > savesegment(gs, prev->gs);
> >+ clearsegment(fs);
> >+ clearsegment(gs);
> >
>
> Really not needed. Think about it. You can even speed up Xen.

Please describe how. I'm afraid I'm missing your point, as I don't see
the improvement.

> I'm glad the native operation here is a nop, but it should be
> hypervisor_clearsegment or xen_clearsegment if you really want to keep it.

Yeah, Andi had similar naming concern.