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

[Zachary Amsden <zach@xxxxxxxxxx>]

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.  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.
Zach

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