From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Borislav Petkov <bp@alien8.de>,
"Bryan O'Donoghue" <pure.logic@nexus-software.ie>,
Andy Lutomirski <luto@amacapital.net>,
Andy Shevchenko <andy.shevchenko@gmail.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
Fenghua Yu <fenghua.yu@intel.com>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Morton <akpm@linux-foundation.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Oleg Nesterov <oleg@redhat.com>,
"Yu, Yu-cheng" <yu-cheng.yu@intel.com>
Subject: Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines
Date: Sat, 12 Mar 2016 16:08:09 +0100 [thread overview]
Message-ID: <20160312150809.GA7015@gmail.com> (raw)
In-Reply-To: <CA+55aFyHQ0+zM5pBNWakA_ti4gutLX5VdounyuduGeFGTmvksg@mail.gmail.com>
* Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Fri, Mar 11, 2016 at 3:32 AM, Borislav Petkov <bp@alien8.de> wrote:
> > 486 cores like Intel Quark support only the very old, legacy x87 FPU
> > (FSAVE/FRSTOR, CPUID bit FXSR is not set). And our FPU code wasn't
> > handling the saving and restoring there properly. First, Andy Shevchenko
> > reported a splat:
> >
> > WARNING: CPU: 0 PID: 823 at arch/x86/include/asm/fpu/internal.h:163 fpu__clear+0x8c/0x160
> >
> > which was us trying to execute FXRSTOR on those machines even though
> > they don't support it.
> >
> > After taking care of that, Bryan O'Donoghue reported that a simple FPU
> > test still failed because we weren't initializing the FPU state properly
> > on those machines.
>
> Obvious Ack to the patch, along with a "how did this ever work
> before?" comment..
So the window for 'real' breakage was relatively short: this is an older bug but
only became a serious bug with the following upcoming commit:
58122bf1d856 x86/fpu: Default eagerfpu=on on all CPUs
... but it's nice to have it fixed nevertheless!
Thanks,
Ingo
next prev parent reply other threads:[~2016-03-12 15:08 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-10 10:46 Got FPU related warning on Intel Quark during boot Andy Shevchenko
2016-03-10 11:19 ` Ingo Molnar
2016-03-10 12:48 ` Andy Shevchenko
2016-03-10 12:56 ` Borislav Petkov
2016-03-10 13:31 ` Andy Shevchenko
2016-03-10 14:59 ` Borislav Petkov
2016-03-10 15:22 ` Andy Shevchenko
2016-03-10 15:45 ` Bryan O'Donoghue
2016-03-10 16:49 ` Borislav Petkov
2016-03-10 17:15 ` Bryan O'Donoghue
2016-03-10 19:06 ` Borislav Petkov
2016-03-11 1:31 ` Andy Lutomirski
2016-03-11 10:50 ` Bryan O'Donoghue
2016-03-11 1:39 ` Andy Lutomirski
2016-03-11 9:08 ` Ingo Molnar
2016-03-11 9:48 ` Borislav Petkov
2016-03-11 11:02 ` Bryan O'Donoghue
2016-03-11 11:26 ` Borislav Petkov
2016-03-11 11:32 ` [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines Borislav Petkov
2016-03-11 18:32 ` Linus Torvalds
2016-03-11 22:03 ` Borislav Petkov
2016-03-11 22:07 ` Dave Hansen
2016-03-11 22:20 ` Borislav Petkov
2016-03-12 17:21 ` Andy Lutomirski
2016-03-12 17:47 ` Borislav Petkov
2016-03-12 12:04 ` Bryan O'Donoghue
2016-03-12 12:27 ` Borislav Petkov
2016-03-12 15:17 ` Ingo Molnar
2016-03-22 22:03 ` Maciej W. Rozycki
2016-03-12 15:08 ` Ingo Molnar [this message]
2016-03-12 15:12 ` Ingo Molnar
2016-03-12 15:16 ` [tip:x86/urgent] x86/fpu: Fix eager-FPU " tip-bot for Borislav Petkov
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