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

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Message-ID: <alpine.LFD.2.20.1603222150460.25290@eddie.linux-mips.org>
Date:	Tue, 22 Mar 2016 22:03:42 +0000 (GMT)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Borislav Petkov <bp@...en8.de>
cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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, 11 Mar 2016, Borislav Petkov wrote:

> > Obvious Ack to the patch, along with a "how did this ever work
> > before?" comment..
> 
> I had a sarcastic sentence in the commit message which I deleted later:
> 
> "Apparently no one had tried the kernel on a 486er after the FPU
> rewrite. Backwards compatibility is overrated."

 People who care do not always have the resources to make regular tests 
with their hardware.

 I for once have meant to check the original series against my 486 EISA 
box since Ingo posted them back in May last year, and I still have them 
stashed away for this purpose.  Unfortunately I didn't get to wire that 
machine for remote console access and power supply control (and I have 
since run out of ports too), so I need to physically get to its location 
to do any testing.

 So it's not unusual for bugs in the less common configurations to only 
surface a bit later on, as people get to making an upgrade.  At least we 
have `git bisect' available and individual changes recorded now, which 
makes tracking down regressions a lot easier than it used to be in the old 
days.

  Maciej