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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A448ACAC587 for ; Thu, 11 Sep 2025 15:31:58 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=n8UjAK5/KbZW/Gzdd4fnBbO0QKUMCsyz9kqqgznPvQg=; b=dPiTUNTQNjuDdedO2RyhChpuy3 5mvVCDYtJDCzjjpYQlriQZrxJCligbluMlX0o83/Y0AOUrGNUelWT4LEH0NoZ5yCBFYLlm0lcDHIb yrKVto7D2a5zAMibyD6aOA18Gd8wlCG9vz1HhGqLUPAkkAcnEWbU07FbL2jFmSoplUTnvrXRUlJRH K7VBASLCbdcZaQQ8gKisDUzYTGTNToQpu//6SIVpTmZsqCPM//SlA4e60tjIPC6YrGLMhDqko1xDJ yFz6sHdLnggqtwQvVHyXbrYrPEEiVr6wD4zM1HOIbPtT91GrfcjrTuZFBxwGPLMpXBTF1qpq2fO5E 4IPK51hQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwjH7-00000003uit-0RsP; Thu, 11 Sep 2025 15:31:53 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1uwjH4-00000003ui7-27ju for linux-arm-kernel@lists.infradead.org; Thu, 11 Sep 2025 15:31:52 +0000 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 C145C153B; Thu, 11 Sep 2025 08:31:40 -0700 (PDT) Received: from [10.1.196.46] (e134344.arm.com [10.1.196.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9D7233F63F; Thu, 11 Sep 2025 08:31:44 -0700 (PDT) Message-ID: Date: Thu, 11 Sep 2025 16:31:43 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 12/29] arm_mpam: Add helpers for managing the locking around the mon_sel registers To: James Morse , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org Cc: D Scott Phillips OS , carl@os.amperecomputing.com, lcherian@marvell.com, bobo.shaobowang@huawei.com, tan.shaopeng@fujitsu.com, baolin.wang@linux.alibaba.com, Jamie Iles , Xin Hao , peternewman@google.com, dfustini@baylibre.com, amitsinght@marvell.com, David Hildenbrand , Dave Martin , Koba Ko , Shanker Donthineni , fenghuay@nvidia.com, baisheng.gao@unisoc.com, Jonathan Cameron , Rob Herring , Rohit Mathew , Rafael Wysocki , Len Brown , Lorenzo Pieralisi , Hanjun Guo , Sudeep Holla , Catalin Marinas , Will Deacon , Greg Kroah-Hartman , Danilo Krummrich References: <20250910204309.20751-1-james.morse@arm.com> <20250910204309.20751-13-james.morse@arm.com> From: Ben Horgan Content-Language: en-US In-Reply-To: <20250910204309.20751-13-james.morse@arm.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250911_083150_671688_85706E0D X-CRM114-Status: GOOD ( 26.53 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi James, On 9/10/25 21:42, James Morse wrote: > The MSC MON_SEL register needs to be accessed from hardirq for the overflow > interrupt, and when taking an IPI to access these registers on platforms > where MSC are not accesible from every CPU. This makes an irqsave > spinlock the obvious lock to protect these registers. On systems with SCMI > mailboxes it must be able to sleep, meaning a mutex must be used. The > SCMI platforms can't support an overflow interrupt. > > Clearly these two can't exist for one MSC at the same time. > > Add helpers for the MON_SEL locking. The outer lock must be taken in a > pre-emptible context before the inner lock can be taken. On systems with > SCMI mailboxes where the MON_SEL accesses must sleep - the inner lock > will fail to be 'taken' if the caller is unable to sleep. This will allow > callers to fail without having to explicitly check the interface type of > each MSC. > > Signed-off-by: James Morse > --- > Change since v1: > * Made accesses to outer_lock_held READ_ONCE() for torn values in the failure > case. > --- > drivers/resctrl/mpam_devices.c | 3 +-- > drivers/resctrl/mpam_internal.h | 37 +++++++++++++++++++++++++++++---- > 2 files changed, 34 insertions(+), 6 deletions(-) > > diff --git a/drivers/resctrl/mpam_devices.c b/drivers/resctrl/mpam_devices.c > index 24dc81c15ec8..a26b012452e2 100644 > --- a/drivers/resctrl/mpam_devices.c > +++ b/drivers/resctrl/mpam_devices.c > @@ -748,8 +748,7 @@ static int mpam_msc_drv_probe(struct platform_device *pdev) > > mutex_init(&msc->probe_lock); > mutex_init(&msc->part_sel_lock); > - mutex_init(&msc->outer_mon_sel_lock); > - raw_spin_lock_init(&msc->inner_mon_sel_lock); > + mpam_mon_sel_lock_init(msc); > msc->id = pdev->id; > msc->pdev = pdev; > INIT_LIST_HEAD_RCU(&msc->all_msc_list); > diff --git a/drivers/resctrl/mpam_internal.h b/drivers/resctrl/mpam_internal.h > index 828ce93c95d5..4cc44d4e21c4 100644 > --- a/drivers/resctrl/mpam_internal.h > +++ b/drivers/resctrl/mpam_internal.h > @@ -70,12 +70,17 @@ struct mpam_msc { > > /* > * mon_sel_lock protects access to the MSC hardware registers that are > - * affected by MPAMCFG_MON_SEL. > + * affected by MPAMCFG_MON_SEL, and the mbwu_state. > + * Access to mon_sel is needed from both process and interrupt contexts, > + * but is complicated by firmware-backed platforms that can't make any > + * access unless they can sleep. > + * Always use the mpam_mon_sel_lock() helpers. > + * Accessed to mon_sel need to be able to fail if they occur in the wrong > + * context. > * If needed, take msc->probe_lock first. > */ > - struct mutex outer_mon_sel_lock; > - raw_spinlock_t inner_mon_sel_lock; > - unsigned long inner_mon_sel_flags; > + raw_spinlock_t _mon_sel_lock; > + unsigned long _mon_sel_flags; > These stale variables can be removed in the patch that introduced them, outer_mon_sel_lock, inner_mon_sel_lock, inner_mon_sel_flags. Jonathan has already pointed out the stale comment and paragraph in the commit message. Thanks, Ben