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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B33DCC38142 for ; Wed, 1 Feb 2023 18:18:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230231AbjBASSb (ORCPT ); Wed, 1 Feb 2023 13:18:31 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55960 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229454AbjBASSa (ORCPT ); Wed, 1 Feb 2023 13:18:30 -0500 Received: from mail.skyhub.de (mail.skyhub.de [IPv6:2a01:4f8:190:11c2::b:1457]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AF1F979202; Wed, 1 Feb 2023 10:18:29 -0800 (PST) Received: from zn.tnic (p5de8e9fe.dip0.t-ipconnect.de [93.232.233.254]) (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 5E9B91EC0426; Wed, 1 Feb 2023 19:18:27 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1675275507; 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=8lNIJZw8YAjz68Gmod7C/9Iqybxq0zMLq+7ven4Sl20=; b=rd8PcoO7dO1r26AupmZg9g2ssXOh16XmgZxt/TK8TJJH1OgIhu6/lH9wA76S90K+LFMgrT VwL+SfBepqKw9QXHKIn8c8TrClQs2hVh5cG0JKZkdOcWtTcGFyqq5wtvF+I2lLA/DXUdq0 EWJtkZg5vKanMrt4rPUJyPH7YgHYHgI= Date: Wed, 1 Feb 2023 19:18:22 +0100 From: Borislav Petkov To: "Edgecombe, Rick P" Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "pavel@ucw.cz" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "linux-doc@vger.kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "Schimpe, Christina" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "akpm@linux-foundation.org" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "andrew.cooper3@citrix.com" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Subject: Re: [PATCH v5 06/39] x86/fpu: Add helper for modifying xstate Message-ID: References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-7-rick.p.edgecombe@intel.com> <095e9694a682fc47ebedd34fddb660319549d6bb.camel@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <095e9694a682fc47ebedd34fddb660319549d6bb.camel@intel.com> Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org On Wed, Feb 01, 2023 at 05:31:50PM +0000, Edgecombe, Rick P wrote: > On Wed, 2023-02-01 at 12:01 +0100, Borislav Petkov wrote: > > On Thu, Jan 19, 2023 at 01:22:44PM -0800, Rick Edgecombe wrote: > > > +void fpregs_lock_and_load(void) > > > +{ > > > + /* > > > + * fpregs_lock() only disables preemption (mostly). So > > > modifying state > > > + * in an interrupt could screw up some in progress fpregs > > > operation, > > > + * but appear to work. Warn about it. > > > > I don't like comments where it sounds like we don't know what we're > > doing. "Appear to work"? > > I can change it. This patch started with the observation that modifying > xstate from the kernel had been gotten wrong a couple times in the > past, so that is what this is referencing. Since then, the fancy > automatic solution got boiled down to this helper and a couple > warnings. Yeah, but that comment right now reads like: modifying in interrupt context can corrupt fpregs and you should not do it but it kinda works, by chance. Thus encouraging people to keep doing that. I guess "but appear to work" can go and then it is fine. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette