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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, 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 23AA4C433DF for ; Mon, 18 May 2020 06:18:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E815720715 for ; Mon, 18 May 2020 06:18:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="e3j2mJNz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726500AbgERGSi (ORCPT ); Mon, 18 May 2020 02:18:38 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37292 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726040AbgERGSh (ORCPT ); Mon, 18 May 2020 02:18:37 -0400 Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D4745C061A0C for ; Sun, 17 May 2020 23:18:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=mi/Yaj0SaOPBvEr8cdz4RwbxKfrvmg/VoMxx24QWS8c=; b=e3j2mJNzk+fSyCgHrmi8Y5KRYB 4BwPvb62ZD3MD9HmtwxBaPKd5lyatjJEwDTnbJa4LHvZzVGftI2H4Dsvz8mLzRiZM5TfVZjQXFPVd oNogyGHS9pKoU2SyE2yndFHNnx335mC8Hk3cMKoheaY4OI66OVMWwItzw6OdoVA6I+vS/Uy/EItNJ 6ALgssZ4/SaDqGyZ+ueYvet/pXld/lzUKFjCYp27Zj53Y034fn9/g9iw1ffRUpHSTOK03dVyBvBds pngg2/befR3UifMqLTWzmU5P0AQkTruuUo0FjYnctUZ5ZSR3Ce2cBkc8SZmtofDNfzn1tt7aumgMA SN14rg0A==; Received: from hch by bombadil.infradead.org with local (Exim 4.92.3 #3 (Red Hat Linux)) id 1jaZ6i-0004VM-LX; Mon, 18 May 2020 06:18:36 +0000 Date: Sun, 17 May 2020 23:18:36 -0700 From: Christoph Hellwig To: Sasha Levin Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, luto@kernel.org, hpa@zytor.com, dave.hansen@intel.com, tony.luck@intel.com, ak@linux.intel.com, ravi.v.shankar@intel.com, chang.seok.bae@intel.com Subject: Re: [PATCH v12 00/18] Enable FSGSBASE instructions Message-ID: <20200518061836.GA15641@infradead.org> References: <20200511045311.4785-1-sashal@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200511045311.4785-1-sashal@kernel.org> X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 11, 2020 at 12:52:53AM -0400, Sasha Levin wrote: > Benefits: > Currently a user process that wishes to read or write the FS/GS base must > make a system call. But recent X86 processors have added new instructions > for use in 64-bit mode that allow direct access to the FS and GS segment > base addresses. The operating system controls whether applications can > use these instructions with a %cr4 control bit. > > In addition to benefits to applications, performance improvements to the > OS context switch code are possible by making use of these instructions. A > third party reported out promising performance numbers out of their > initial benchmarking of the previous version of this patch series [9]. The [9] reference can't be resolved anywhere in this mail.