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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 5F6F5C433E0 for ; Mon, 22 Jun 2020 17:09:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2968D20707 for ; Mon, 22 Jun 2020 17:09:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="i2/KkFrf" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729873AbgFVRJO (ORCPT ); Mon, 22 Jun 2020 13:09:14 -0400 Received: from mail.skyhub.de ([5.9.137.197]:46366 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729840AbgFVRJM (ORCPT ); Mon, 22 Jun 2020 13:09:12 -0400 Received: from zn.tnic (p200300ec2f0a2500329c23fffea6a903.dip0.t-ipconnect.de [IPv6:2003:ec:2f0a:2500:329c:23ff:fea6:a903]) (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 B9E141EC0283; Mon, 22 Jun 2020 19:09:10 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1592845750; 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=Y3LIWY+KnYvD5SmbVfic/Btuy5xncoQOY7OQQwRbvX0=; b=i2/KkFrfoUY4Gm7+vsS+DhMOqAxrQJ3GDR4nNNh9ZeY0p1Pq7EQzLEm1NNkNa+n0CBe7p7 lvVAq8r3213Y49iamCrLnk4B5DBrCcW3MLLJplti2WAZ183ra7AY9sEk3rsPHzPMffHptg P1zEmlxLUHqehLwkoLQ2CU5vgOC4yoE= Date: Mon, 22 Jun 2020 19:09:08 +0200 From: Borislav Petkov To: Andy Lutomirski Cc: X86 ML , jpa@kernelbug.mail.kapsi.fi, Dave Hansen , LKML Subject: Re: [PATCH 1/2] x86/fpu: Reset MXCSR to default in kernel_fpu_begin() Message-ID: <20200622170908.GH32200@zn.tnic> References: <20200619174127.22304-1-bp@alien8.de> <20200619174127.22304-2-bp@alien8.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Jun 19, 2020 at 11:01:44AM -0700, Andy Lutomirski wrote: > On Fri, Jun 19, 2020 at 10:41 AM Borislav Petkov wrote: > > > > From: Petteri Aimonen > > > > Previously, kernel floating point code would run with the MXCSR control > > register value last set by userland code by the thread that was active > > on the CPU core just before kernel call. This could affect calculation > > results if rounding mode was changed, or a crash if a FPU/SIMD exception > > was unmasked. > > > > Restore MXCSR to the kernel's default value. > > > > [ bp: Carve out from a bigger patch by Petteri, add feature check, add > > FNINIT call too (amluto). ] > > Acked-by: Andy Lutomirski > > but: > > shouldn't kernel_fpu_begin() end with a barrier()? the "fninit" thing is already asm volatile or do you want the explicit memory clobber of barrier? If so, why? The LDMXCSR and FNINIT have effect only on hardware state... -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette