linux-kernel - Re: Wrong defaults in 3.7-rc3

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Message-ID: <50A6B0E6.2010608@linux.intel.com>
Date:	Fri, 16 Nov 2012 13:32:22 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Pavel Machek <pavel@....cz>
CC:	kernel list <linux-kernel@...r.kernel.org>, mchehab@...hat.com
Subject: Re: Wrong defaults in 3.7-rc3

On 11/15/2012 03:06 AM, Pavel Machek wrote:
> Hi!
> 
> Supervisor Mode Access Prevention (X86_SMAP) [Y/n/?] (NEW)
> 
> ...Slows stuff down, eats memory, only works on unreleased Intel CPUs
> (from 2013!)  perhaps should be off by default?
> 
> "Supervisor Mode Access Prevention (SMAP) is a security
> feature in newer Intel processors.  There is a small
> performance cost if this enabled and turned on; there is
> also a small increase in the kernel size if this is enabled."
> 

*Extremely* small.  Unless you are targeting a specific processor there
is no point in disabling it.  If anyone can find a non-SMAP processor on
which the overhead is measurable I would be highly surprised, except
perhaps some embedded 486 clone.

	-hpa

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