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

[Chris Wright]

* Zachary Amsden (zach@xxxxxxxxxx) 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.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/