linux-kernel - Re: [GIT PULL] x86 FPU changes for 5.2

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Message-ID: <CAHk-=wh4Cjb1qDj_VRW9W4d4n9WLksgMKF-roG8eCk_O0ZaEEg@mail.gmail.com>
Date:   Tue, 7 May 2019 10:35:25 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Borislav Petkov <bp@...e.de>
Cc:     Rik van Riel <riel@...riel.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        x86-ml <x86@...nel.org>, lkml <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] x86 FPU changes for 5.2

On Tue, May 7, 2019 at 6:26 AM Borislav Petkov <bp@...e.de> wrote:
>
> This branch contains work started by Rik van Riel and brought to
> fruition by Sebastian Andrzej Siewior with the main goal to optimize
> when to load FPU registers: only when returning to userspace and not on
> every context switch (while the task remains in the kernel).

I love this and we should have done it long ago, but I also worry that
every time we've messed with the FP state, we've had interesting bugs.
Which is obviously why we didn't do this long ago.

Has this gone through lots of testing, particularly with things like
FP signal handling and old machines that don't necessarily have
anything but the most basic FP state (ie Pentium class etc)?

I've pulled it, but I'd still like to feel safer about it after-the-fact ;)

               Linus