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 334CDC433FE for ; Thu, 24 Nov 2022 14:21:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229610AbiKXOVj (ORCPT ); Thu, 24 Nov 2022 09:21:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52326 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229570AbiKXOVg (ORCPT ); Thu, 24 Nov 2022 09:21:36 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 5C0C4D5A for ; Thu, 24 Nov 2022 06:21:35 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 57B8B23A; Thu, 24 Nov 2022 06:21:41 -0800 (PST) Received: from [10.1.197.38] (eglon.cambridge.arm.com [10.1.197.38]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id DABAA3F73B; Thu, 24 Nov 2022 06:21:31 -0800 (PST) Message-ID: <7a942c00-67a9-c038-b516-4ae85e997a6e@arm.com> Date: Thu, 24 Nov 2022 14:21:25 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101 Thunderbird/91.13.0 Subject: Re: [PATCH 07/18] x86/resctrl: Move CLOSID/RMID matching and setting to use helpers Content-Language: en-GB To: Valentin Schneider , x86@kernel.org, linux-kernel@vger.kernel.org Cc: Fenghua Yu , Reinette Chatre , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Babu Moger , shameerali.kolothum.thodi@huawei.com, D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, Jamie Iles , Xin Hao , xingxin.hx@openanolis.org, baolin.wang@linux.alibaba.com, peternewman@google.com References: <20221021131204.5581-1-james.morse@arm.com> <20221021131204.5581-8-james.morse@arm.com> From: James Morse In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Valentin, On 18/11/2022 15:49, Valentin Schneider wrote: > On 21/10/22 13:11, James Morse wrote: >> When switching tasks, the CLOSID and RMID that the new task should >> use are stored in struct task_struct. For x86 the CLOSID known by resctrl, >> the value in task_struct, and the value written to the CPU register are >> all the same thing. >> >> MPAM's CPU interface has two different PARTID's one for data accesses >> the other for instruction fetch. Storing resctrl's CLOSID value in >> struct task_struct implies the arch code knows whether resctrl is using >> CDP. >> >> Move the matching and setting of the struct task_struct properties >> to use helpers. This allows arm64 to store the hardware format of >> the register, instead of having to convert it each time. >> >> __rdtgroup_move_task()s use of READ_ONCE()/WRITE_ONCE() ensures torn >> values aren't seen as another CPU may schedule the task being moved >> while the value is being changed. MPAM has an additional corner-case >> here as the PMG bits extend the PARTID space. If the scheduler sees a >> new-CLOSID but old-RMID, the task will dirty an RMID that the limbo code >> is not watching causing an inaccurate count. x86's RMID are independent >> values, so the limbo code will still be watching the old-RMID in this >> circumstance. >> To avoid this, arm64 needs both the CLOSID/RMID WRITE_ONCE()d together. >> Both values must be provided together. > I think I remember something about this... Is that about having them > union'd and read/written as one? (just for my own curiosity) Yup. Many moons ago you pointed out that storing partid/pmg separately lets the remote CPUs load torn values. arm64 not only needs the values as a pair, it needs to read/write them as a pair. >> Because MPAM's RMID values are not unique, the CLOSID must be provided >> when matching the RMID. >> >> CC: Valentin Schneider (CC here also stands for celebrate-contribution!) >> Signed-off-by: James Morse > > Reviewed-by: Valentin Schneider Thanks! James