Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932596AbbD0KJx (ORCPT <rfc822;w@1wt.eu>);
	Mon, 27 Apr 2015 06:09:53 -0400
Received: from mail.skyhub.de ([78.46.96.112]:41654 "EHLO mail.skyhub.de"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S932130AbbD0KJu (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 27 Apr 2015 06:09:50 -0400
Date: Mon, 27 Apr 2015 12:09:34 +0200
From: Borislav Petkov <bp@alien8.de>
To: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>, Andy Lutomirski <luto@kernel.org>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Denys Vlasenko <vda.linux@googlemail.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Brian Gerst <brgerst@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor
 attribute issue
Message-ID: <20150427100934.GE6774@pd.tnic>
References: <5d120f358612d73fc909f5bfa47e7bd082db0af0.1429841474.git.luto@kernel.org>
 <20150425211206.GE32099@pd.tnic>
 <CALCETrWvqyCYOzCYXz7ZnzaM0obbidqo5CxVp2Hn1ELEiC3m3g@mail.gmail.com>
 <20150427085305.GB6774@pd.tnic>
 <553E0A52.7070400@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <553E0A52.7070400@redhat.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 940
Lines: 29

On Mon, Apr 27, 2015 at 12:07:14PM +0200, Denys Vlasenko wrote:
> 	/* Only three 0x66 prefixes for NOP for fast decode on all CPUs */
> 	ALTERNATIVE	".byte 0x66,0x66,0x66,0x90 \
> 			.byte 0x66,0x66,0x66,0x90 \
> 			.byte 0x66,0x66,0x66,0x90",
> 			"shl	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx \
> 			sar	$(64 - (__VIRTUAL_MASK_SHIFT+1)), %rcx \
> 			cmpq	%rcx, %r11 \
> 			jne	opportunistic_sysret_failed"
> 			X86_BUG_SYSRET_CANONICAL_RCX
> 
> would be better than letting ALTERNATIVE to generate 13 one-byte NOPs.

We already do everything automagically, see:
arch/x86/kernel/alternative.c: optimize_nops()

:-)

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/