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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 B15F3C3F2D2 for ; Fri, 28 Feb 2020 18:31:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 89881246A3 for ; Fri, 28 Feb 2020 18:31:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="mmrGt5hO" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726627AbgB1Sbi (ORCPT ); Fri, 28 Feb 2020 13:31:38 -0500 Received: from mail.skyhub.de ([5.9.137.197]:53560 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725827AbgB1Sbi (ORCPT ); Fri, 28 Feb 2020 13:31:38 -0500 Received: from zn.tnic (p200300EC2F084600A41928AC2BDFCE32.dip0.t-ipconnect.de [IPv6:2003:ec:2f08:4600:a419:28ac:2bdf:ce32]) (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 937B21EC0235; Fri, 28 Feb 2020 19:31:36 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1582914696; 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:in-reply-to:in-reply-to: references:references; bh=vKcgGMDU+mnrcvNjUC9MBKQ22KHBpf5+JRGEkK8GD44=; b=mmrGt5hOFiItfdIEDb54DKRpElQ5SdUE70XxYSUujJGPd9YCt2RyhbS2cETMY0MhylblVb r8MpT8zC1m30xyb0VzgNBbUT7By6qrp4YHRcE3xntTzslXJ+R4sVMuANZ8UrUkJLYhVndp yy91QM/mxtRwjc3QD9j3UlMP52PFPNo= Date: Fri, 28 Feb 2020 19:31:31 +0100 From: Borislav Petkov To: Yu-cheng Yu 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 Subject: Re: [PATCH v2 8/8] x86/fpu/xstate: Restore supervisor xstates for __fpu__restore_sig() Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <9a283ad42da140d73de680b1975da142e62e016e.camel@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > 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? -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette