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 BF9D3C43334 for ; Wed, 15 Jun 2022 13:02:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345746AbiFONCe (ORCPT ); Wed, 15 Jun 2022 09:02:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41540 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1346242AbiFONCb (ORCPT ); Wed, 15 Jun 2022 09:02:31 -0400 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6D30595A6 for ; Wed, 15 Jun 2022 06:02:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1655298150; x=1686834150; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=9aFgN11zv32epzY4IsX2SnErbjKpIlBDe1HikVsn+0U=; b=LQXTLOxF4unUQnOQYNk9Pc2R8WlDQASeZg4Gi15t15k5Vcb4YpUTUUHy oMI6vB8QKgpHNMXM6K9EUr09P+buvYhXDeqrV/cZiPGE8GQSb6hW3sxT9 7S6JBP8/HxZWVPQlXITwLeyhO+DFMtrCc73XmZhrgxSlkZduLKgJEddHh rSz9t9bhhuxc1NdzKSMS/WmZOnIW5HcN7AO/dnOotNvG9gQOMEMZC/KsH lISDk+VUt7oGeNXqMgvoM9XoqxjRa4/mG+VFM+xhRDcz6346+++1DIpME SHmwKJIf9VwyJNHYoL/kNqrHjkIn1TbRqnitdkkO66UVoCpB13T9vVrkW w==; X-IronPort-AV: E=McAfee;i="6400,9594,10378"; a="267641909" X-IronPort-AV: E=Sophos;i="5.91,302,1647327600"; d="scan'208";a="267641909" Received: from fmsmga007.fm.intel.com ([10.253.24.52]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2022 06:02:29 -0700 X-IronPort-AV: E=Sophos;i="5.91,302,1647327600"; d="scan'208";a="589103071" Received: from leitan-mobl.ccr.corp.intel.com (HELO [10.255.31.142]) ([10.255.31.142]) by fmsmga007-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jun 2022 06:02:27 -0700 Message-ID: <08fd79a1-0117-42bb-9105-c8ff400fb7df@linux.intel.com> Date: Wed, 15 Jun 2022 21:02:25 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.9.1 Cc: baolu.lu@linux.intel.com, Will Deacon , Robin Murphy , "Liu, Yi L" , "Pan, Jacob jun" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v2 01/12] iommu/vt-d: debugfs: Remove device_domain_lock usage Content-Language: en-US To: "Tian, Kevin" , Joerg Roedel , "Raj, Ashok" , Christoph Hellwig , Jason Gunthorpe References: <20220614025137.1632762-1-baolu.lu@linux.intel.com> <20220614025137.1632762-2-baolu.lu@linux.intel.com> <4f6f7bb9-5ea4-b466-7a59-62ebd5bc2cf7@linux.intel.com> From: Baolu Lu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2022/6/15 14:13, Tian, Kevin wrote: >> From: Baolu Lu >> Sent: Wednesday, June 15, 2022 9:54 AM >> >> On 2022/6/14 14:43, Tian, Kevin wrote: >>>> From: Lu Baolu >>>> Sent: Tuesday, June 14, 2022 10:51 AM >>>> >>>> The domain_translation_struct debugfs node is used to dump the DMAR >>>> page >>>> tables for the PCI devices. It potentially races with setting domains to >>>> devices. The existing code uses a global spinlock device_domain_lock to >>>> avoid the races, but this is problematical as this lock is only used to >>>> protect the device tracking lists of each domain. >>> is it really problematic at this point? Before following patches are applied >>> using device_domain_lock should have similar effect as holding the group >>> lock. >>> >>> Here it might make more sense to just focus on removing the use of >>> device_domain_lock outside of iommu.c. Just that using group lock is >>> cleaner and more compatible to following cleanups. >>> >>> and it's worth mentioning that racing with page table updates is out >>> of the scope of this series. Probably also add a comment in the code >>> to clarify this point. >>> >> Hi Kevin, >> >> How do you like below updated patch? > Yes, this is better. > >> From cecc9a0623780a11c4ea4d0a15aa6187f01541c4 Mon Sep 17 00:00:00 >> 2001 >> From: Lu Baolu >> Date: Sun, 29 May 2022 10:18:56 +0800 >> Subject: [PATCH 1/1] iommu/vt-d: debugfs: Remove device_domain_lock >> usage >> >> The domain_translation_struct debugfs node is used to dump the DMAR >> page >> tables for the PCI devices. It potentially races with setting domains to >> devices. The existing code uses the global spinlock device_domain_lock to >> avoid the races. >> >> This removes the use of device_domain_lock outside of iommu.c by replacing >> it with the group mutex lock. Using the group mutex lock is cleaner and >> more compatible to following cleanups. >> >> Signed-off-by: Lu Baolu >> --- >> drivers/iommu/intel/debugfs.c | 42 +++++++++++++++++++++++++---------- >> drivers/iommu/intel/iommu.c | 2 +- >> drivers/iommu/intel/iommu.h | 1 - >> 3 files changed, 31 insertions(+), 14 deletions(-) >> >> diff --git a/drivers/iommu/intel/debugfs.c b/drivers/iommu/intel/debugfs.c >> index d927ef10641b..f4acd8993f60 100644 >> --- a/drivers/iommu/intel/debugfs.c >> +++ b/drivers/iommu/intel/debugfs.c >> @@ -342,13 +342,13 @@ static void pgtable_walk_level(struct seq_file *m, >> struct dma_pte *pde, >> } >> } >> >> -static int show_device_domain_translation(struct device *dev, void *data) >> +static int __show_device_domain_translation(struct device *dev, void *data) >> { >> - struct device_domain_info *info = dev_iommu_priv_get(dev); >> - struct dmar_domain *domain = info->domain; >> + struct dmar_domain *domain; >> struct seq_file *m = data; >> u64 path[6] = { 0 }; >> >> + domain = to_dmar_domain(iommu_get_domain_for_dev(dev)); >> if (!domain) >> return 0; >> >> @@ -359,20 +359,38 @@ static int show_device_domain_translation(struct >> device *dev, void *data) >> pgtable_walk_level(m, domain->pgd, domain->agaw + 2, 0, path); >> seq_putc(m, '\n'); >> >> - return 0; >> + return 1; >> } >> >> -static int domain_translation_struct_show(struct seq_file *m, void *unused) >> +static int show_device_domain_translation(struct device *dev, void *data) >> { >> - unsigned long flags; >> - int ret; >> + struct iommu_group *group; >> >> - spin_lock_irqsave(&device_domain_lock, flags); >> - ret = bus_for_each_dev(&pci_bus_type, NULL, m, >> - show_device_domain_translation); >> - spin_unlock_irqrestore(&device_domain_lock, flags); >> + group = iommu_group_get(dev); >> + if (group) { >> + /* >> + * The group->mutex is held across the callback, which will >> + * block calls to iommu_attach/detach_group/device. Hence, >> + * the domain of the device will not change during traversal. >> + * >> + * All devices in an iommu group share a single domain, >> hence >> + * we only dump the domain of the first device. Even though, > bus_for_each_dev() will still lead to duplicated dump in the same group > but probably we can leave with it for a debug interface. > Yes. This is what it was. Ideally we could walk the iommu groups and dump the device names belonging to the group and it's domain mappings, but I was not willing to add any helpers in the iommu core just for a debugfs use. --- Best regards, baolu