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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 107D7C433FE for ; Tue, 16 Nov 2021 09:42:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DA12C61B29 for ; Tue, 16 Nov 2021 09:42:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233267AbhKPJpP (ORCPT ); Tue, 16 Nov 2021 04:45:15 -0500 Received: from mga03.intel.com ([134.134.136.65]:11756 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233149AbhKPJpN (ORCPT ); Tue, 16 Nov 2021 04:45:13 -0500 X-IronPort-AV: E=McAfee;i="6200,9189,10169"; a="233599062" X-IronPort-AV: E=Sophos;i="5.87,238,1631602800"; d="scan'208";a="233599062" Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Nov 2021 01:42:14 -0800 X-IronPort-AV: E=Sophos;i="5.87,238,1631602800"; d="scan'208";a="506359272" Received: from blu2-mobl3.ccr.corp.intel.com (HELO [10.254.210.220]) ([10.254.210.220]) by orsmga008-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 16 Nov 2021 01:42:07 -0800 Message-ID: <14bed5c1-a385-7e99-bda9-1041341fe68d@linux.intel.com> Date: Tue, 16 Nov 2021 17:42:04 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.3.0 Cc: baolu.lu@linux.intel.com, Greg Kroah-Hartman , Joerg Roedel , Alex Williamson , Bjorn Helgaas , Jason Gunthorpe , Kevin Tian , Ashok Raj , Chaitanya Kulkarni , kvm@vger.kernel.org, rafael@kernel.org, linux-pci@vger.kernel.org, Cornelia Huck , linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org, Jacob jun Pan , Diana Craciun , Will Deacon Content-Language: en-US To: Christoph Hellwig References: <20211115020552.2378167-1-baolu.lu@linux.intel.com> <20211115020552.2378167-7-baolu.lu@linux.intel.com> From: Lu Baolu Subject: Re: [PATCH 06/11] iommu: Expose group variants of dma ownership interfaces In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Hi Christoph, On 2021/11/15 21:27, Christoph Hellwig wrote: > On Mon, Nov 15, 2021 at 10:05:47AM +0800, Lu Baolu wrote: >> The vfio needs to set DMA_OWNER_USER for the entire group when attaching > > The vfio subsystem? driver? "vfio subsystem" > >> it to a vfio container. So expose group variants of setting/releasing dma >> ownership for this purpose. >> >> This also exposes the helper iommu_group_dma_owner_unclaimed() for vfio >> report to userspace if the group is viable to user assignment, for > > .. for vfio to report .. ? Yes. > >> void iommu_device_release_dma_owner(struct device *dev, enum iommu_dma_owner owner); >> +int iommu_group_set_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner, >> + struct file *user_file); >> +void iommu_group_release_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner); > > Pleae avoid all these overly long lines. Sure. Thanks! > >> +static inline int iommu_group_set_dma_owner(struct iommu_group *group, >> + enum iommu_dma_owner owner, >> + struct file *user_file) >> +{ >> + return -EINVAL; >> +} >> + >> +static inline void iommu_group_release_dma_owner(struct iommu_group *group, >> + enum iommu_dma_owner owner) >> +{ >> +} >> + >> +static inline bool iommu_group_dma_owner_unclaimed(struct iommu_group *group) >> +{ >> + return false; >> +} > > Why do we need these stubs? All potential callers should already > require CONFIG_IOMMU_API? Same for the helpers added in patch 1, btw. You are right. This helper is only for vfio which requires IOMMU_API. I will remove this. The helpers in patch 1 seem not the same. The driver core (or bus dma_configure() callback as suggested) will also call them. > >> + mutex_lock(&group->mutex); >> + ret = __iommu_group_set_dma_owner(group, owner, user_file); >> + mutex_unlock(&group->mutex); > >> + mutex_lock(&group->mutex); >> + __iommu_group_release_dma_owner(group, owner); >> + mutex_unlock(&group->mutex); > > Unless I'm missing something (just skipping over the patches), > the existing callers also take the lock just around these calls, > so we don't really need the __-prefixed lowlevel helpers. > Move mutex_lock/unlock will make the helper implementation easier. :-) It seems to be common code style in iommu core. For example, __iommu_attach_group(), __iommu_group_for_each_dev(), etc. >> + mutex_lock(&group->mutex); >> + owner = group->dma_owner; >> + mutex_unlock(&group->mutex); > > No need for a lock to read a single scalar. Adding the lock will make kcasn happy. Jason G also told me that [citing from his review comment] " It is always incorrect to read concurrent data without an annotation of some kind. For instance it can cause mis-execution of logic where the compiler is unaware that a value it loads is allowed to change - ie no READ_ONCE/WRITE_ONCE semantic. " > >> + >> + return owner == DMA_OWNER_NONE; >> +} >> +EXPORT_SYMBOL_GPL(iommu_group_dma_owner_unclaimed); Best regards, baolu