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=-0.8 required=3.0 tests=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 617CDC3F2CD for ; Fri, 28 Feb 2020 21:23:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3DFD2246AE for ; Fri, 28 Feb 2020 21:23:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727005AbgB1VX3 (ORCPT ); Fri, 28 Feb 2020 16:23:29 -0500 Received: from mga03.intel.com ([134.134.136.65]:30031 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725805AbgB1VX3 (ORCPT ); Fri, 28 Feb 2020 16:23:29 -0500 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Feb 2020 13:23:28 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.70,497,1574150400"; d="scan'208";a="385611917" Received: from yyu32-desk.sc.intel.com ([143.183.136.146]) by orsmga004.jf.intel.com with ESMTP; 28 Feb 2020 13:23:27 -0800 Message-ID: <7c6560b067436e2ec52121bba6bff64833e28d8d.camel@intel.com> Subject: Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for __fpu__restore_sig() From: Yu-cheng Yu To: Borislav Petkov Cc: linux-kernel@vger.kernel.org, x86@kernel.org, "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , Dave Hansen , Tony Luck , Andy Lutomirski , Rik van Riel , "Ravi V. Shankar" , Sebastian Andrzej Siewior , Fenghua Yu , Peter Zijlstra Date: Fri, 28 Feb 2020 13:22:39 -0800 In-Reply-To: <20200228183131.GE25261@zn.tnic> References: <20200121201843.12047-1-yu-cheng.yu@intel.com> <20200121201843.12047-9-yu-cheng.yu@intel.com> <20200221175859.GL25747@zn.tnic> <77f3841a92df5d0c819699ee3612118d566b7445.camel@intel.com> <20200228121724.GA25261@zn.tnic> <89bcab262d6dad4c08c4a21e522796fea2320db3.camel@intel.com> <20200228162359.GC25261@zn.tnic> <6f91699c91f9ea0f527e80ed3ea2999444a8d2d1.camel@intel.com> <20200228172202.GD25261@zn.tnic> <9a283ad42da140d73de680b1975da142e62e016e.camel@intel.com> <20200228183131.GE25261@zn.tnic> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.32.4 (3.32.4-1.fc30) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 2020-02-28 at 19:31 +0100, Borislav Petkov wrote: > On Fri, Feb 28, 2020 at 10:11:44AM -0800, Yu-cheng Yu wrote: > > CET has 16 bytes for ring-3 setting, 24 bytes for ring-0. > > Saving supervisor states somewhere else and copying back is not better > > either. > > Well, if you're going to save a lot bigger user states area which is > going to be absolutely wasted cycles in that case, you better save those > couple of bytes in another buffer and then copy them into the final state > buffer which gets restored. The code is for sigreturn only. Because of lazy-restore, copy_xregs_to_kernel() does not happen all the time. It is attractive in terms of simplicity. XSAVES buffer has fixed 576-byte overhead (512-byte legacy + 64-byte header) and not suitable for partial saving. To save only supervisor states, we need to read out each MSR separately and store them in a struct. > > > We save supervisor states only when xfeatures_mask_supervisor() is not > > zero. > > And on which systems is it not zero? On systems which have supervisor > features or on systems which have *and* *are* *using* supervisor > features? On systems using supervisor features. Yu-cheng