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 7C2ABC433EF for ; Wed, 30 Mar 2022 16:45:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348949AbiC3QrB (ORCPT ); Wed, 30 Mar 2022 12:47:01 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40358 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1348916AbiC3Qq4 (ORCPT ); Wed, 30 Mar 2022 12:46:56 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id CE06F2013F4 for ; Wed, 30 Mar 2022 09:45:10 -0700 (PDT) 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 8D4EA1576; Wed, 30 Mar 2022 09:45:10 -0700 (PDT) Received: from [10.1.196.218] (eglon.cambridge.arm.com [10.1.196.218]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id B34053F73B; Wed, 30 Mar 2022 09:45:08 -0700 (PDT) Subject: Re: [PATCH v3 16/21] x86/resctrl: Pass the required parameters into resctrl_arch_rmid_read() To: Rob Herring Cc: x86@kernel.org, linux-kernel@vger.kernel.org, Fenghua Yu , Reinette Chatre , Thomas Gleixner , Ingo Molnar , Borislav Petkov , H Peter Anvin , Babu Moger , shameerali.kolothum.thodi@huawei.com, Jamie Iles , D Scott Phillips OS , lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com References: <20220217182110.7176-1-james.morse@arm.com> <20220217182110.7176-17-james.morse@arm.com> From: James Morse Message-ID: <4b1cc5a9-a081-bbc9-40af-e8e33061e64e@arm.com> Date: Wed, 30 Mar 2022 17:45:03 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Rob, On 23/03/2022 20:58, Rob Herring wrote: > On Thu, Feb 17, 2022 at 06:21:05PM +0000, James Morse wrote: >> resctrl_arch_rmid_read() is intended as the function that an >> architecture agnostic resctrl filesystem driver can use to >> read a value in bytes from a hardware register. Currently the function >> returns the MBM values in chunks directly from hardware. >> >> To convert this to bytes, some correction and overflow calculations >> are needed. These depend on the resource and domain structures. >> Overflow detection requires the old chunks value. None of this >> is available to resctrl_arch_rmid_read(). MPAM requires the >> resource and domain structures to find the MMIO device that holds >> the registers. >> diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c >> index b6ad290fda8d..277c22f8c976 100644 >> --- a/arch/x86/kernel/cpu/resctrl/monitor.c >> +++ b/arch/x86/kernel/cpu/resctrl/monitor.c >> @@ -167,10 +167,14 @@ void resctrl_arch_reset_rmid(struct rdt_resource *r, struct rdt_domain *d, >> memset(am, 0, sizeof(*am)); >> } >> >> -int resctrl_arch_rmid_read(u32 rmid, enum resctrl_event_id eventid, u64 *val) >> +int resctrl_arch_rmid_read(struct rdt_resource *r, struct rdt_domain *d, >> + u32 rmid, enum resctrl_event_id eventid, u64 *val) >> { >> u64 msr_val; >> >> + if (!cpumask_test_cpu(smp_processor_id(), &d->cpu_mask)) > We already tested this and disabled preemption. (At least from some > caller AFAICT from this patch.) I'd assume we'd want the fs code to > handle preemption disable and checking cpumask. In any case, it should > be clear what guarantees resctrl_arch_rmid_read() has. This started as a lockdep warning for things that don't matter on x86, but would break arm64. Combined with some half baked thinking about RT. I'll add a comment, (in the header file). It needs to be called on the correct CPU, but from process context as MPAM needs to send IPI from here. I didn't want to add a preempt_disable() lockdep annotation here as its not pre-emption that's the problem, but migration. cqm_handle_limbo() and mbm_handle_overflow() are the two main routes in here, and they both use schedule_delayed_work_on() to target the 'correct' CPU. Thanks, James