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 02:18:17PM -0700, Yu-cheng Yu wrote:
> Before Linux gets into copy_fpstate_to_sigframe(),
> current->thread.fpu.fpstate_active must be true.
> For eagerfpu, fpregs_active() must also be true.
> For lazyfpu, once we try to do FSAVE/FXSAVE/XSAVE,
> fpregs_active() will become true as well.
> 
> We should have not based on boot_cpu_has(X86_FEATURE_XSAVES)
> at all. 
> 
> Why don't we make it simple and always copy_fpregs_to_signal_frame()?
> Or, only for the lazy case, i.e. !fpregs_active(), we do __copy_to_user().

For (lazy && not XSAVES) actually!