linux-kernel - Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute issue

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Message-ID: <553E8C3E.8040701@redhat.com>
Date:	Mon, 27 Apr 2015 21:21:34 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Andy Lutomirski <luto@...capital.net>,
	Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Denys Vlasenko <vda.linux@...glemail.com>,
	Brian Gerst <brgerst@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Will Drewry <wad@...omium.org>,
	Kees Cook <keescook@...omium.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute
 issue

On 04/27/2015 09:11 PM, Borislav Petkov wrote:
> A:     709.528485252 seconds time elapsed                                          ( +-  0.02% )
> B:     708.976557288 seconds time elapsed                                          ( +-  0.04% )
> C:     709.312844791 seconds time elapsed                                          ( +-  0.02% )
> D:     709.400050112 seconds time elapsed                                          ( +-  0.01% )
> E:     708.914562508 seconds time elapsed                                          ( +-  0.06% )
> F:     709.602255085 seconds time elapsed                                          ( +-  0.02% )

That's about 0.2% variance. Very small.

Sounds obvious, but. Did you try running a test several times?
Maybe you are measuring random noise.


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