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 BDE54C43334 for ; Tue, 14 Jun 2022 07:16:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353467AbiFNHQG (ORCPT ); Tue, 14 Jun 2022 03:16:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54736 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238909AbiFNHQE (ORCPT ); Tue, 14 Jun 2022 03:16:04 -0400 Received: from mga06.intel.com (mga06b.intel.com [134.134.136.31]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BA4FF3C492 for ; Tue, 14 Jun 2022 00:16:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1655190963; x=1686726963; h=message-id:date:mime-version:cc:subject:to:references: from:in-reply-to:content-transfer-encoding; bh=NHeKt8AVVuoNMGzSRtkrNqEDEEKj+JEu5vZWp4ee3Qg=; b=cjlCv+XWZIgicX2Qa5dl/Y7wwZaEtz0Daa1Kl/JLjZDinXBJrnH0eTtc icXRIyGl2BGjXHNemrGap+zAsq483hd2cNqbSWUTlf0UsF8n0zbieNh3Q NvMqykvJs4iGOCP89g5HnZKnYRAr9xg+lOKsJm99MISy+HtF/j51NPeE1 nlDd1xjz00vXdGfzGgNwT5kfVrjFaCxqWHrXyZBXFbE4YpOdq4+AdLeZ/ 2z0GiVQtVzbneIFoKZRLAMlQZPIRXGiKIyWLcdH21xoWKcJTVQfAvtqaP wEyAAdvrZAZRID71tasDn/eTO2HlKgDrVMQ58nb+RMKN3Rr94ygwrQKg4 Q==; X-IronPort-AV: E=McAfee;i="6400,9594,10377"; a="340200762" X-IronPort-AV: E=Sophos;i="5.91,299,1647327600"; d="scan'208";a="340200762" Received: from fmsmga005.fm.intel.com ([10.253.24.32]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2022 00:15:53 -0700 X-IronPort-AV: E=Sophos;i="5.91,299,1647327600"; d="scan'208";a="910834149" Received: from gren5-mobl1.ccr.corp.intel.com (HELO [10.255.29.39]) ([10.255.29.39]) by fmsmga005-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 14 Jun 2022 00:15:50 -0700 Message-ID: <1161fe02-7dbb-6f97-39c0-a84be016e0a9@linux.intel.com> Date: Tue, 14 Jun 2022 15:15:48 +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> 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 Hi Kevin, Thanks for your reviewing. 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. The device_domain_lock only protects the device tracking list of the domain, it doesn't include the domain pointer stored in the dev_info structure. That's really protected by the group->mutex. > > 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. Fair enough. I will update the commit message with above statement. > 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. Sure. > >> >> This replaces device_domain_lock with group->mutex to protect page tables >> from setting a new domain. This also makes device_domain_lock static as >> it is now only used inside the file. > > s/the file/iommu.c/ Sure. > >> >> Signed-off-by: Lu Baolu >> --- >> drivers/iommu/intel/iommu.h | 1 - >> drivers/iommu/intel/debugfs.c | 49 +++++++++++++++++++++++++---------- >> drivers/iommu/intel/iommu.c | 2 +- >> 3 files changed, 36 insertions(+), 16 deletions(-) >> >> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h >> index a22adfbdf870..8a6d64d726c0 100644 >> --- a/drivers/iommu/intel/iommu.h >> +++ b/drivers/iommu/intel/iommu.h >> @@ -480,7 +480,6 @@ enum { >> #define VTD_FLAG_SVM_CAPABLE (1 << 2) >> >> extern int intel_iommu_sm; >> -extern spinlock_t device_domain_lock; >> >> #define sm_supported(iommu) (intel_iommu_sm && >> ecap_smts((iommu)->ecap)) >> #define pasid_supported(iommu) (sm_supported(iommu) && >> \ >> diff --git a/drivers/iommu/intel/debugfs.c b/drivers/iommu/intel/debugfs.c >> index d927ef10641b..5ebfe32265d5 100644 >> --- a/drivers/iommu/intel/debugfs.c >> +++ b/drivers/iommu/intel/debugfs.c >> @@ -342,15 +342,23 @@ static void pgtable_walk_level(struct seq_file *m, >> struct dma_pte *pde, >> } >> } >> >> -static int show_device_domain_translation(struct device *dev, void *data) >> +struct show_domain_opaque { >> + struct device *dev; >> + struct seq_file *m; >> +}; > > Sounds redundant as both bus_for_each_dev() and > iommu_group_for_each_dev() declares the same fn type which > accepts a device pointer and 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 seq_file *m = data; >> + struct show_domain_opaque *opaque = data; >> + struct device_domain_info *info; >> + struct seq_file *m = opaque->m; >> + struct dmar_domain *domain; >> u64 path[6] = { 0 }; >> >> - if (!domain) >> + if (dev != opaque->dev) >> return 0; > > not required. Together with above comment. The iommu group might have other devices. I only want to dump the domain of the secific @opaque->dev. It reads a bit confusing, but it's the only helper I can use outside of drivers/iommu/iommu.c. Or, since all devices in the iommu group share the same domain, hence only dump once? > >> + info = dev_iommu_priv_get(dev); >> + domain = info->domain; >> >> seq_printf(m, "Device %s @0x%llx\n", dev_name(dev), >> (u64)virt_to_phys(domain->pgd)); >> @@ -359,20 +367,33 @@ 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 show_domain_opaque opaque = {dev, data}; >> + 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. >> + */ >> + iommu_group_for_each_dev(group, &opaque, >> + __show_device_domain_translation); >> + iommu_group_put(group); >> + } >> >> - return ret; >> + return 0; >> +} >> + >> +static int domain_translation_struct_show(struct seq_file *m, void *unused) >> +{ >> + return bus_for_each_dev(&pci_bus_type, NULL, m, >> + show_device_domain_translation); >> } >> DEFINE_SHOW_ATTRIBUTE(domain_translation_struct); >> >> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c >> index 19024dc52735..a39d72a9d1cf 100644 >> --- a/drivers/iommu/intel/iommu.c >> +++ b/drivers/iommu/intel/iommu.c >> @@ -314,7 +314,7 @@ static int iommu_skip_te_disable; >> #define IDENTMAP_GFX 2 >> #define IDENTMAP_AZALIA 4 >> >> -DEFINE_SPINLOCK(device_domain_lock); >> +static DEFINE_SPINLOCK(device_domain_lock); >> static LIST_HEAD(device_domain_list); >> >> /* >> -- >> 2.25.1 > Best regards, baolu