RE: [patch 5/6] x86/fpu: Provide fpu_update_guest_xcr0/xfd()

[Tian, Kevin]

> From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Sent: Thursday, December 16, 2021 10:13 PM
> >
> > Yes, this is the 3rd open that I asked in another reply. The only restriction
> > with this approach is that the sync cost is added also for legacy OS which
> > doesn't touch xfd at all.
> 
> You still can make that conditional on the guest XCR0. If guest never
> enables the extended bit then neither the #NM trap nor the XFD sync
> are required.
> 
> But yes, there are too many moving parts here :)
> 

Yes. Many moving parts but in general it's getting cleaner and simplified. 😊

We just sent out v2 to hopefully lock down already-closed opens. Based on
that we can see what remains to be further solved.

And really appreciate all the suggestions from you and Paolo!

Thanks
Kevin