linux-kernel - Re: [PATCH 02/19] x86, fpu: Wrap get_xsave

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Message-ID: <20150529161036.GK31435@pd.tnic>
Date:	Fri, 29 May 2015 18:10:36 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Dave Hansen <dave@...1.net>, Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	X86 ML <x86@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Suresh Siddha <sbsiddha@...il.com>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 02/19] x86, fpu: Wrap get_xsave_addr() to make it safer

On Thu, May 28, 2015 at 06:05:33PM -0700, Andy Lutomirski wrote:
> I would propose that we take the opposite approach and just ban
> eagerfpu=off when MPX is enabled.  We could then take the next step
> and default eagerfpu=on for everyone and, if nothing breaks, then just
> delete lazy mode entirely.
> 
> I suspect we'd have to go back to Pentium 3 or earlier to find a CPU
> on which lazy mode is actually a good idea.

Last time I checked (and ran some benchmarks) it was only a minute
slowdown so I say we kill lazy mode if it means significant code
complexity drop.

Can I also emulate Greg here and suggest that Pentium 3 people should
buy newer hw? They should think about the environment, if nothing else.

:-P

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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