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

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Message-ID: <20190507175913.GC26655@zn.tnic>
Date:   Tue, 7 May 2019 19:59:13 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
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 07, 2019 at 10:35:25AM -0700, Linus Torvalds wrote:
> 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.

Tell me about it. Our FPU code is one helluva contraption.

> 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)?

Right, so I ran it on the bunch of boxes I have here, the oldest is a K8
which has:

[    0.000000] x86/fpu: x87 FPU will use FXSAVE

and it looked ok. Ingo ran it on his fleet too, AFAIR.

Lemme see if I can dig out something older at work.

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

Yeah.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Mary Higgins, Sri Rasiah, HRB 21284 (AG Nürnberg)