linux-kernel - Re: [PATCH v2 0/6] iommu: Extend changing default domain to normal group

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Date:   Fri, 17 Feb 2023 11:47:52 -0400
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux.dev, Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/6] iommu: Extend changing default domain to normal
 group

On Fri, Feb 17, 2023 at 05:47:30PM +0800, Lu Baolu wrote:
> The IOMMU group sysfs interface allows users to change the default
> domain of a group. The current implementation uses device_lock() to make
> sure that the devices in the group are not bound to any driver and won't
> be bound during the process of changing the default domain. In order to
> avoid a possible deadlock caused by lock order of device_lock and
> group->mutex, it limits the functionality to singleton groups only.
> 
> The recently implemented DMA ownership framework can be applied here to
> replace device_lock(). In addition, use group->mutex to ensure that the
> iommu ops of the devices is always valid during the process of changing
> default domain.
> 
> With above replacement and enhancement, the device_lock() could be
> removed and the singleton-group-only limitation could be removed.
> 
> The whole series is also available on github:
> https://github.com/LuBaolu/intel-iommu/commits/iommu-sysfs-default-domain-extension-v2
> 
> This series is on top of below series from Robin,
> https://lore.kernel.org/linux-iommu/cover.1674753627.git.robin.murphy@arm.com/
> 
> Please help to review and suggest.

Given the overall situation, I think my suggestion to use
arm_iommu_release_device() might be more short term practical.

Jason