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

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Date:	Fri, 12 Dec 2014 08:40:29 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 12/10/2014 12:49 PM, Linus Torvalds wrote:
> On Wed, Dec 10, 2014 at 12:39 PM, Dave Hansen
> <dave.hansen@...ux.intel.com> wrote:
>>
>> I misspoke there.  I meant SMAP (I placed MPX below its config option).
> 
> Ok, I agree on SMAP, we might want to have that be configurable too,
> especially for smaller systems (I *think* SMAP is big-core only,
> right?). I'm not sure how much of a possible performance downside it
> has, but it does add instructions to potentially critical areas.
> 

*As far as I know*, SMAP will be pushed into all CPUs over time.

SMAP is already configurable, although the overhead on non-SMAP-enabled
hardware is minimal (the CLAC/STAC instructions get patched out.)

	-hpa


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