From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id AC8EEC64E7C for ; Wed, 2 Dec 2020 17:09:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 42ACD217A0 for ; Wed, 2 Dec 2020 17:09:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728774AbgLBRJJ (ORCPT ); Wed, 2 Dec 2020 12:09:09 -0500 Received: from mail.skyhub.de ([5.9.137.197]:39802 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727126AbgLBRJI (ORCPT ); Wed, 2 Dec 2020 12:09:08 -0500 Received: from zn.tnic (p200300ec2f161b00329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ec:2f16:1b00:329c:23ff:fea6:a903]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 88AA91EC0445; Wed, 2 Dec 2020 18:08:27 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1606928907; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=5ySegBj5bw98Dubr8StQaVFXEi9kv05WveRbfqUYjPM=; b=nupJKD0sLAJ4R4UUPVoZaW60JPZLoqvGYStCVadIUPeYcxQBDe1TC8TasvCIz+cBpUSJMI dbbQFVbpPp5/4n1DfFyfcTn82NsC40ZfhEmqPlVJx0HXns7PsZW4zbP9lny+lXVOb5CUuO WZuBUXZ7PtfjieBd/pKYBpU6ZLcKRCA= Date: Wed, 2 Dec 2020 18:08:23 +0100 From: Borislav Petkov To: =?utf-8?B?SsO8cmdlbiBHcm/Dnw==?= Cc: xen-devel@lists.xenproject.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, peterz@infradead.org, luto@kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , Deep Shah , "VMware, Inc." , Boris Ostrovsky , Stefano Stabellini Subject: Re: [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call Message-ID: <20201202170823.GF2951@zn.tnic> References: <20201120114630.13552-1-jgross@suse.com> <20201120114630.13552-5-jgross@suse.com> <20201202123235.GD2951@zn.tnic> <6be0d1a5-0079-5d90-0c38-85fe4471f1b8@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <6be0d1a5-0079-5d90-0c38-85fe4471f1b8@suse.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 02, 2020 at 03:48:21PM +0100, Jürgen Groß wrote: > I wanted to avoid the additional NOPs for the bare metal case. Yeah, in that case it gets optimized to a single NOP: [ 0.176692] SMP alternatives: ffffffff81a00068: [0:5) optimized NOPs: 0f 1f 44 00 00 which is nopl 0x0(%rax,%rax,1) and I don't think that's noticeable on modern CPUs where a NOP is basically a rIP increment only and that goes down the pipe almost for free. :-) > If you don't mind them I can do as you are suggesting. Yes pls, I think asm readability is more important than a 5-byte NOP. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette