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=-4.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, URIBL_BLOCKED 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 E32A6C5ACCC for ; Tue, 16 Oct 2018 23:00:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F9912148C for ; Tue, 16 Oct 2018 23:00:38 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="Yjr71oq+" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8F9912148C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727111AbeJQGxO (ORCPT ); Wed, 17 Oct 2018 02:53:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:46774 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726697AbeJQGxO (ORCPT ); Wed, 17 Oct 2018 02:53:14 -0400 Received: from mail-wr1-f42.google.com (mail-wr1-f42.google.com [209.85.221.42]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 12DF22148C for ; Tue, 16 Oct 2018 23:00:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1539730836; bh=AtVdJg1PwWul3p9fkSe8Cet8TQhp0Y3/AYVopGoCJGA=; h=References:In-Reply-To:From:Date:Subject:To:Cc:From; b=Yjr71oq+dd3SFO9GFAcKWoDBi2pl8g58F524dbBQn0PQxpdQMXX22c6JAlmZsz74s XqcoRzeQqkeQvutRKhFkpDzOqSAiLLhZPUI4YLIxEDtD/96Q8KNUYoPqkEj+/NV0yW R3cNpdTHWnXWKz1sl3eVIjiyaxEUs5672uByHo9s= Received: by mail-wr1-f42.google.com with SMTP id e4-v6so27450507wrs.0 for ; Tue, 16 Oct 2018 16:00:36 -0700 (PDT) X-Gm-Message-State: ABuFfog3rZOUbSUr+Q1tabW/JuUsd/BSjh9iP5aU/cgxg2ASQ2O4ppxn WF3cmWAqqFsAkZSBP/WWQtxFuFK5QzjsOMekSQ2kRQ== X-Google-Smtp-Source: ACcGV61HojzK4sloNz8mOLGwzYXljhCb7vqPRFIGAHpotHaKwNWNOrKVj2W0fIYI8n2h20fYR8ttg5zv4wUy17zZeiY= X-Received: by 2002:adf:b188:: with SMTP id q8-v6mr20798323wra.95.1539730834546; Tue, 16 Oct 2018 16:00:34 -0700 (PDT) MIME-Version: 1.0 References: <20181016202525.29437-1-bigeasy@linutronix.de> <20181016202525.29437-4-bigeasy@linutronix.de> In-Reply-To: <20181016202525.29437-4-bigeasy@linutronix.de> From: Andy Lutomirski Date: Tue, 16 Oct 2018 16:00:23 -0700 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [PATCH 3/3] x86/fpu: Save FPU registers on context switch if there is a FPU To: Sebastian Andrzej Siewior Cc: LKML , X86 ML , Dave Hansen , Andrew Lutomirski , Peter Zijlstra , Borislav Petkov , stable 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, Oct 16, 2018 at 1:25 PM Sebastian Andrzej Siewior wrote: > > Booting a 486 with "no387 nofxsr" ends with > | math_emulate: 0060:c101987d > | Kernel panic - not syncing: Math emulation needed in kernel > > on the first context switch in user land. The reason is that > copy_fpregs_to_fpstate() tries `fnsave' which does not work. This > happens since commit f1c8cd0176078 ("x86/fpu: Change fpu->fpregs_active > users to fpu->fpstate_active"). > > Add a check for X86_FEATURE_FPU before trying to save FPU registers (we > have such a check switch_fpu_finish() already). > > Fixes: f1c8cd0176078 ("x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active") > Cc: stable@vger.kernel.org > Signed-off-by: Sebastian Andrzej Siewior Reviewed-by: Andy Lutomirski