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 32C86C43334 for ; Sun, 17 Jul 2022 07:55:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232809AbiGQHzL (ORCPT ); Sun, 17 Jul 2022 03:55:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36172 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229476AbiGQHzJ (ORCPT ); Sun, 17 Jul 2022 03:55:09 -0400 Received: from wp530.webpack.hosteurope.de (wp530.webpack.hosteurope.de [IPv6:2a01:488:42:1000:50ed:8234::]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9377115834; Sun, 17 Jul 2022 00:55:08 -0700 (PDT) Received: from [2a02:8108:963f:de38:eca4:7d19:f9a2:22c5]; authenticated by wp530.webpack.hosteurope.de running ExIM with esmtpsa (TLS1.3:ECDHE_RSA_AES_128_GCM_SHA256:128) id 1oCz7G-0003PZ-5e; Sun, 17 Jul 2022 09:55:02 +0200 Message-ID: Date: Sun, 17 Jul 2022 09:55:00 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.11.0 Subject: Re: [PATCH 0/3] x86: make pat and mtrr independent from each other Content-Language: en-US To: Juergen Gross , xen-devel@lists.xenproject.org, x86@kernel.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org Cc: brchuckz@netscape.net, jbeulich@suse.com, Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , "# 5 . 17" , "Rafael J. Wysocki" , Pavel Machek , Andy Lutomirski , Peter Zijlstra , Boris Ostrovsky References: <20220715142549.25223-1-jgross@suse.com> From: Thorsten Leemhuis In-Reply-To: <20220715142549.25223-1-jgross@suse.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-bounce-key: webpack.hosteurope.de;regressions@leemhuis.info;1658044508;3110b8b4; X-HE-SMSGID: 1oCz7G-0003PZ-5e Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org Hi Juergen! On 15.07.22 16:25, Juergen Gross wrote: > Today PAT can't be used without MTRR being available, unless MTRR is at > least configured via CONFIG_MTRR and the system is running as Xen PV > guest. In this case PAT is automatically available via the hypervisor, > but the PAT MSR can't be modified by the kernel and MTRR is disabled. > > As an additional complexity the availability of PAT can't be queried > via pat_enabled() in the Xen PV case, as the lack of MTRR will set PAT > to be disabled. This leads to some drivers believing that not all cache > modes are available, resulting in failures or degraded functionality. > > The same applies to a kernel built with no MTRR support: it won't > allow to use the PAT MSR, even if there is no technical reason for > that, other than setting up PAT on all cpus the same way (which is a > requirement of the processor's cache management) is relying on some > MTRR specific code. > > Fix all of that by: > > - moving the function needed by PAT from MTRR specific code one level > up > - adding a PAT indirection layer supporting the 3 cases "no or disabled > PAT", "PAT under kernel control", and "PAT under Xen control" > - removing the dependency of PAT on MTRR Thx for working on this. If you need to respin these patches for one reason or another, could you do me a favor and add proper 'Link:' tags pointing to all reports about this issue? e.g. like this: Link: https://lore.kernel.org/regressions/YnHK1Z3o99eMXsVK@mail-itl/ These tags are considered important by Linus[1] and others, as they allow anyone to look into the backstory weeks or years from now. That is why they should be placed in cases like this, as Documentation/process/submitting-patches.rst and Documentation/process/5.Posting.rst explain in more detail. I care personally, because these tags make my regression tracking efforts a whole lot easier, as they allow my tracking bot 'regzbot' to automatically connect reports with patches posted or committed to fix tracked regressions. [1] see for example: https://lore.kernel.org/all/CAHk-=wjMmSZzMJ3Xnskdg4+GGz=5p5p+GSYyFBTh0f-DgvdBWg@mail.gmail.com/ https://lore.kernel.org/all/CAHk-=wgs38ZrfPvy=nOwVkVzjpM3VFU1zobP37Fwd_h9iAD5JQ@mail.gmail.com/ https://lore.kernel.org/all/CAHk-=wjxzafG-=J8oT30s7upn4RhBs6TX-uVFZ5rME+L5_DoJA@mail.gmail.com/ Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat) P.S.: As the Linux kernel's regression tracker I deal with a lot of reports and sometimes miss something important when writing mails like this. If that's the case here, don't hesitate to tell me in a public reply, it's in everyone's interest to set the public record straight. BTW, let me tell regzbot to monitor this thread: #regzbot ^backmonitor: https://lore.kernel.org/regressions/YnHK1Z3o99eMXsVK@mail-itl/