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=-4.0 required=3.0 tests=BAYES_00,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 A0836C63777 for ; Thu, 3 Dec 2020 11:46:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4764D20758 for ; Thu, 3 Dec 2020 11:46:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730323AbgLCLqI (ORCPT ); Thu, 3 Dec 2020 06:46:08 -0500 Received: from mail.kernel.org ([198.145.29.99]:32774 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726038AbgLCLqI (ORCPT ); Thu, 3 Dec 2020 06:46:08 -0500 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0198D20758; Thu, 3 Dec 2020 11:45:27 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kkn36-00FeCw-K0; Thu, 03 Dec 2020 11:45:24 +0000 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Thu, 03 Dec 2020 11:45:24 +0000 From: Marc Zyngier To: Rongwei Wang Cc: catalin.marinas@arm.com, Will Deacon , bjorn.andersson@linaro.org, shawnguo@kernel.org, gshan@redhat.com, geert+renesas@glider.be, Anson.Huang@nxp.com, masahiroy@kernel.org, michael@walle.cc, krzk@kernel.org, linux-kernel@vger.kernel.org, vkoul@kernel.org, olof@lixom.net, vincenzo.frascino@arm.com, ardb@kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver In-Reply-To: <58C4701C-DEAC-4FE9-B54C-3B9ADC8E197D@linux.alibaba.com> References: <20201130174833.41315-1-rongwei.wang@linux.alibaba.com> <5e7f7225982b2df63e62ea60ec632376@misterjones.org> <855BA92C-5B22-4F14-965A-B1F72A872B8D@linux.alibaba.com> <059ed4a8768ff3881005796cb4a10d5e@kernel.org> <6FA68A07-F718-46F5-81B4-586A5ED3E479@linux.alibaba.com> <7e9ae04f3394a85aa3b8fe8947a44009@kernel.org> <4513911D-77BF-4459-B8DF-9889395C16AC@linux.alibaba.com> <4f89671e080eb23b084c0e0942f111e6@kernel.org> <58C4701C-DEAC-4FE9-B54C-3B9ADC8E197D@linux.alibaba.com> User-Agent: Roundcube Webmail/1.4.9 Message-ID: <6698aa55cf4ee69a18049c4bf8a21c4f@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: rongwei.wang@linux.alibaba.com, catalin.marinas@arm.com, will@kernel.org, bjorn.andersson@linaro.org, shawnguo@kernel.org, gshan@redhat.com, geert+renesas@glider.be, Anson.Huang@nxp.com, masahiroy@kernel.org, michael@walle.cc, krzk@kernel.org, linux-kernel@vger.kernel.org, vkoul@kernel.org, olof@lixom.net, vincenzo.frascino@arm.com, ardb@kernel.org, linux-arm-kernel@lists.infradead.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2020-12-03 11:25, Rongwei Wang wrote: >> 2020年12月3日 下午4:35，Marc Zyngier 写道： [...] >> But what does it mean to change random system registers while the >> kernel >> itself is using them in parallel? All you are introducing is a bunch >> of >> uncontrolled, unexpected, and possibly fatal side effects. > This problem exists when writing to a register, but it does not exist > when reading a register. If you're not aware that the ARM architecture does have system registers with read side-effects, you really shouldn't be writing this code. M. -- Jazz is not dead. It just smells funny...