linux-kernel - Re: [GIT pull] x86 mpx support for 3.19

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Message-ID: <CA+55aFwTpZ8U7vUvBE8xkX1_vfktyVDcCwchssMhhP44M8TzUg@mail.gmail.com>
Date:	Wed, 10 Dec 2014 11:49:58 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Hansen <dave.hansen@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [GIT pull] x86 mpx support for 3.19

On Wed, Dec 10, 2014 at 11:41 AM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> But, this is the kind of option that we want to be *sure* is enabled
> unless folks know exactly what they are doing, so we should probably
> hide it behind CONFIG_EXPERT as well, just as SMEP is.

I disagree.

SMEP doesn't have any performance overhead, and SMEP is available in
processors available today. So SMEP doesn't even have a config option,
because there is no downside with having it on and enabled.

MPX, in contrast, you don't even normally want to run at all as a
normal user because of the overheads. That's going to be true even
when it's available.

So I would claim the exact reverse: right now, enabling MPX should be
something only experts should do.

                  Linus
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