Re: [PATCH RFC 1/3] fpu/x86: add make_fpregs_active(_newstate) helper functions

From: Andy Lutomirski
Date: Mon Oct 17 2016 - 19:31:20 EST

On Mon, Oct 17, 2016 at 4:04 PM, Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:
> On Mon, Oct 17, 2016 at 01:57:06PM -0700, Andy Lutomirski wrote:
>> Dave and/or Yu-cheng: didn't one of you have some code to allow a user
>> xstate buffer to be filled from the copy in kernel memory? If we did
>> that, we could avoid this mess entirely.
> In copy_fpstate_to_sigframe() (arch/x86/kernel/fpu/signal.c), the
> assumption was we have lazy fpu:
> if (fpregs_active() || we want an #NM exception)
> copy_fpregs_to_sigframe();
> else
> copy kernel buffer to user buffer;
> But this is not the true anymore. Or do you mean something else?

Rik wants to add a different form of FPU laziness, and it would be
simpler if we could just always copy from a kernel buffer. Does code
to do that exist in the tree?