Re: [Xen-devel] fpu_taskswitch adjustment proposal

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.06.12 at 14:12, Keir Fraser <keir@xxxxxxx> wrote:
> On 18/06/2012 08:32, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>>> It should be possible for the guest kernel to track its CR0.TS setting
>>> shouldn't it? It gets modified only via a few paravirt hooks, and implicitly
>>> cleared on #NM.
>> 
>> Sure, but selling this to the Linux maintainers I would expect to be
>> harder than fitting the Xen side of things into the current save-
>> and-restore model the native xor code uses. It would only be strait
>> forward to implement on the legacy, forward ported trees.
> 
> Wouldn't it be hidden entirely behind pv_ops hooks and within Xen-specific
> SSE save/restore code? I suppose you'd need to statically allocate the
> per-cpu space for tracking the CR0.TS state... But overall it seems it will
> be of little/no concern to other kernel maintainers?

The #NM handler part wouldn't afaict. Everything else indeed
ought to be restricted to the functions backing paravirt.h's clts()
and write_cr0().

Jan


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