linux-kernel - Re: [PATCH v3 0/7] x86: Pile o' FS/GS changes

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Message-ID: <20160408103939.GE29522@pd.tnic>
Date:	Fri, 8 Apr 2016 12:39:39 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	security@...nel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Rudolf Marek <r.marek@...embler.cz>
Subject: Re: [PATCH v3 0/7] x86: Pile o' FS/GS changes

On Thu, Apr 07, 2016 at 05:31:43PM -0700, Andy Lutomirski wrote:
> Hi all-
> 
> This whole mess is intended for x86/urgent.  It fixes several bugs.
> 
> It's probably a tiny performance regression on some workloads on
> Intel CPUs.  It's probably varies between a less tiny regression and
> a small speedup on newer AMD CPUs.  It's a bigger regression on AMD
> K8.

Shhh, otherwise the 2-3 K8 users left would crawl out of the woodwork
complaining. ;-)

> The AMD code could be further sped up by adding a new 'clear_gs'
> pvop with a better native implementation.  I don't particularly want
> to deal with a backported new pvop, so I didn't do that.  Maybe I'll
> do it later on for new kernels, though.

Yeah, before you do that, we should probably measure that first to see
whether it is worth the trouble and the added pvop gunk at all.

-- 
Regards/Gruss,
    Boris.

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