linux-kernel - Re: [PATCH RFC v3 02/12] iommu: Add a flag to indicate immutable singleton group

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Date:   Tue, 12 Apr 2022 19:56:14 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Yi Liu <yi.l.liu@...el.com>, "Tian, Kevin" <kevin.tian@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>
Cc:     baolu.lu@...ux.intel.com, Eric Auger <eric.auger@...hat.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC v3 02/12] iommu: Add a flag to indicate immutable
 singleton group

Hi Yi,

On 2022/4/12 14:34, Yi Liu wrote:
>>>
>>>>
>>>> This adds a flag in the iommu_group struct to indicate an immutable
>>>> singleton group, and uses standard PCI bus topology, isolation 
>>>> features,
>>>> and DMA alias quirks to set the flag. If the device came from DT, 
>>>> assume
>>>> it is static and then the singleton attribute can know from the device
>>>> count in the group.
>>>
>>> where does the assumption come from?
>>
>> Hotplug is the only factor that can dynamically affect the
>> characteristics of IOMMU group singleton as far as I can see. If a
>> device node was created from the DT, it could be treated as static,
>> hence we can judge the singleton in iommu probe phase during boot.
> 
> not sure if hotplug is the only factor. Is it possible that admin modifies
> the ACS configuration on the bridge?

Not likely. This will completely change the existing iommu_group
settings.

Best regards,
baolu