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=-1.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, T_DKIMWL_WL_HIGH autolearn=ham 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 673E4C004C9 for ; Tue, 7 May 2019 17:35:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A92C205C9 for ; Tue, 7 May 2019 17:35:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1557250547; bh=QpGCIYI22OmPrtKNZByqkY/eP0ucnMsjEQvSLHbvg1k=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=vLRdIJo1mu05hBSQkYcxs3XjG0EMMc80VEEwUDS+p0XzBFCYvjz+DlupU7l7CsCe0 UgQ+iX2+G7AEKLlXF/gzHsW2iFYxW9rxzWyC1VLbzRBhp/QI+Vry/BcnWDDnW6sUZE DKhEX/xsZKeuvkUrHqROhOpI41CnrudHR3DkeJtk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727486AbfEGRfq (ORCPT ); Tue, 7 May 2019 13:35:46 -0400 Received: from mail-lj1-f195.google.com ([209.85.208.195]:34387 "EHLO mail-lj1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726378AbfEGRfp (ORCPT ); Tue, 7 May 2019 13:35:45 -0400 Received: by mail-lj1-f195.google.com with SMTP id s7so9662103ljh.1 for ; Tue, 07 May 2019 10:35:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=ffMscuu3PUeSeZb5tEXYoJU5cfVCzk2YToQl4OvjLZo=; b=H36Gpb50r9djkhKtwQe3VJpRaLJw/NGSVDsmjM54fy8tMa/SUIs7pLVJp581T7Ys20 8jaYXH5Sh569s93/hVFiq5rZNQH56hFJ256xdH0tmNKP7Bczg/VWm64TU4aXNw+s8jYx QPwg4iTwOqo5JQRRyAhG7MhENuqZqg3/ZjtCY= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=ffMscuu3PUeSeZb5tEXYoJU5cfVCzk2YToQl4OvjLZo=; b=avoNHA8uhHsme46qtZNDJqubeUWlcYtKDXP5vXpfKMhn8xXrQ1zk98+3UAjbtSMQNJ /VNV88i1IZeWVD7r1744jiyEMa6/dS3wZouzpZ/l18Su52ZOVWzXi72/NBE0hD0MFLQg Ck7+gl23bzuQ+uchjBOc0ED4wd74BcNnLLUHU+Wl8TDdpZ/+r8xgRn5kpESWPRpTaP9s sj/eRQe/PSl2YldGZtRjlkps695ZjW9HC214ogXxXmMtSB957QjbeEebzOHHIT4Pj4HU ycE0PziYJzgMGKgP4wJVGjDFNYTHWv56rEesGN+ShTTcMZnfJ3vTkyv4gPQlyk+lDMib pIzg== X-Gm-Message-State: APjAAAUguZsQg4bkHafTkhYgKEcYWKyfthChkSHoQ6vyA2d/WvQeDia+ fR0lfPdqEvxdiCJqbDT91i/dPV3S5gI= X-Google-Smtp-Source: APXvYqwFJpJXFt96v/SD14kBNrxVfKAZLRK1VmtiPPnMg+AnbG9Y4epOcpzSkLsERghqOkMKe6tTBA== X-Received: by 2002:a2e:9d12:: with SMTP id t18mr18474297lji.163.1557250543289; Tue, 07 May 2019 10:35:43 -0700 (PDT) Received: from mail-lf1-f49.google.com (mail-lf1-f49.google.com. [209.85.167.49]) by smtp.gmail.com with ESMTPSA id a6sm538720lfi.89.2019.05.07.10.35.42 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 07 May 2019 10:35:42 -0700 (PDT) Received: by mail-lf1-f49.google.com with SMTP id d8so12449469lfb.8 for ; Tue, 07 May 2019 10:35:42 -0700 (PDT) X-Received: by 2002:ac2:43cf:: with SMTP id u15mr17155883lfl.67.1557250541931; Tue, 07 May 2019 10:35:41 -0700 (PDT) MIME-Version: 1.0 References: <20190507132632.GB26655@zn.tnic> In-Reply-To: <20190507132632.GB26655@zn.tnic> From: Linus Torvalds Date: Tue, 7 May 2019 10:35:25 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [GIT PULL] x86 FPU changes for 5.2 To: Borislav Petkov Cc: Rik van Riel , Sebastian Andrzej Siewior , x86-ml , lkml Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 7, 2019 at 6:26 AM Borislav Petkov wrote: > > This branch contains work started by Rik van Riel and brought to > fruition by Sebastian Andrzej Siewior with the main goal to optimize > when to load FPU registers: only when returning to userspace and not on > every context switch (while the task remains in the kernel). I love this and we should have done it long ago, but I also worry that every time we've messed with the FP state, we've had interesting bugs. Which is obviously why we didn't do this long ago. Has this gone through lots of testing, particularly with things like FP signal handling and old machines that don't necessarily have anything but the most basic FP state (ie Pentium class etc)? I've pulled it, but I'd still like to feel safer about it after-the-fact ;) Linus