Re: [PATCH v4 04/10] x86/xsaves: Introduce a new check that allows correct xstates copy from kernel to user directly

[Yu-cheng Yu]

On Mon, May 02, 2016 at 09:06:41AM -0700, Dave Hansen wrote:
> On 05/02/2016 08:57 AM, Yu-cheng Yu wrote:
> > On Fri, Apr 29, 2016 at 05:36:48PM -0700, Dave Hansen wrote:
> >> If may_copy_fpregs_to_sigframe() were called from a slightly different
> >> context, or if we change the call-site, what breaks?
> >>
> >> In other words. if we can still "may_copy_fpregs_to_sigframe()" no
> >> matter the state of fpu.fpstate_active, then I don't think we should be
> >> checking it in may_copy_fpregs_to_sigframe().
> > 
> > Do you mean, don't check fpu.fpstate_active here?
> 
> Not really.  I'm asking *why* the check is there.

If (fpu.fpstate_active == 0), then the task does not use FPU; we don't
want to save these registers, right?