linux-kernel - Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines

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Date:	Fri, 11 Mar 2016 10:32:43 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Ingo Molnar <mingo@...nel.org>,
	"Bryan O'Donoghue" <pure.logic@...us-software.ie>,
	Andy Lutomirski <luto@...capital.net>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Fenghua Yu <fenghua.yu@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"Yu, Yu-cheng" <yu-cheng.yu@...el.com>
Subject: Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines

On Fri, Mar 11, 2016 at 3:32 AM, Borislav Petkov <bp@...en8.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..

           Linus