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

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Date:   Sat, 18 Feb 2023 15:31:47 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, 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 2/17/23 11:47 PM, Jason Gunthorpe wrote:
> 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.

Yes. Fair enough.

Best regards,
baolu