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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY 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 221D5C63777 for ; Thu, 3 Dec 2020 05:46:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0E3120B80 for ; Thu, 3 Dec 2020 05:46:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728441AbgLCFqW convert rfc822-to-8bit (ORCPT ); Thu, 3 Dec 2020 00:46:22 -0500 Received: from out30-43.freemail.mail.aliyun.com ([115.124.30.43]:44625 "EHLO out30-43.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727937AbgLCFqW (ORCPT ); Thu, 3 Dec 2020 00:46:22 -0500 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04423;MF=rongwei.wang@linux.alibaba.com;NM=1;PH=DS;RN=17;SR=0;TI=SMTPD_---0UHNyBks_1606974337; Received: from 30.27.144.231(mailfrom:rongwei.wang@linux.alibaba.com fp:SMTPD_---0UHNyBks_1606974337) by smtp.aliyun-inc.com(127.0.0.1); Thu, 03 Dec 2020 13:45:38 +0800 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.4 \(3608.120.23.2.4\)) Subject: Re: [PATCH 0/3] arm64:msr: Add MSR driver From: Rongwei Wang In-Reply-To: <7e9ae04f3394a85aa3b8fe8947a44009@kernel.org> Date: Thu, 3 Dec 2020 13:45:36 +0800 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 Content-Transfer-Encoding: 8BIT Message-Id: <4513911D-77BF-4459-B8DF-9889395C16AC@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> To: Marc Zyngier X-Mailer: Apple Mail (2.3608.120.23.2.4) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > 2020年12月1日 下午11:37，Marc Zyngier 写道： > > On 2020-12-01 14:25, wangrongwei wrote: >>> 2020年12月1日 下午4:12，Marc Zyngier 写道： >>> On 2020-12-01 03:09, wangrongwei wrote: >>>> Hi >>>> We have validate this driver in vm and physical machine, and works fine. >>> But what does "work fine" mean? None of these system registers are supposed >>> to be accessible from userspace, so please explain *what* you are trying to >>> do with this, other that introducing security holes and general system >>> instability? >> I think I know what you mean. Do you want me to describe how we achieved it? >> In x86, the different registers can be accessed directly using the >> rdmsr and wrmsr instructions, but in ARM, since these two instructions >> are missing, so we modify the code segment during runtime, similar to >> the principle of static_key. > > [...] > > These are implementation details, none of which answer my question: > > What makes you think this is a good idea? I cannot see any legitimate In fact, I think this tool useful mainly in the following scenarios: 1. performance debug 2. Arm-core features test 3. Debug-tool for kernel developer Also, for example, MSR-ARM is needed for chip verification and system-level functional verification. A simple example, perf stat can test pmu, but the overflow interrupt function and forced overflow function of pmu is not covered. In both cases, we need a special interface to configure it, which can be considered as testing requirements, so it can only be tested by configuring (access) registers, e.g., devmem command for memmap registers, MSR-ARM driver for system registers. > reason for userspace to ever access privileged system registers, and > the fact that x86 has such feature isn't a good justification. > > M. > -- > Jazz is not dead. It just smells funny… Sorry for the delayed response. Regards, Rongwei Wang.