linux-kernel - Re: [PATCH RFC 1/3] fpu/x86: add make_fpregs_active(

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Date:   Mon, 17 Oct 2016 16:04:17 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Rik van Riel <riel@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Lutomirski <luto@...nel.org>,
        dave.hansen@...el.linux.com, Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC 1/3] fpu/x86: add make_fpregs_active(_newstate)
 helper functions

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?

-- Yu-cheng