linux-kernel - Re: [PATCH v10 04/12] iommu: Add attach/detach_dev

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Message-ID: <f1908476-8f83-5467-9172-ec0b7838e67a@linux.intel.com>
Date:   Sat, 30 Jul 2022 14:23:15 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        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>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        Zhangfei Gao <zhangfei.gao@...aro.org>,
        "Zhu, Tony" <tony.zhu@...el.com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: Re: [PATCH v10 04/12] iommu: Add attach/detach_dev_pasid iommu
 interface

On 2022/7/29 20:22, Jason Gunthorpe wrote:
> The RID issue is that we can't reliably tell the source apart in a
> group - so all the RIDs in a group have to be considered as the same
> RID, and mapped to the same PASID table.
> 
> But that is the only restriction of a group we have left, because the
> 'iommu doesn't isolate all traffic' restriction is defined not to
> exist if PASID is supported.

Get you. Thank you for the guide.

> 
>> So yes, from this angle leaving one table per group is a simpler
>> thing to do, especially when it's unclear whether there is real
>> demand to enable PASID for multi-device group. 😊
> Except it is confusing, complicated and unnecessary. Treating PASID of
> multi-device groups the same as everything else is logically simple.

Yes. Considering that current PASID use cases occur only on singleton
groups, to make things simple, let's start our PASID attachment support
simply from singleton groups.

Best regards,
baolu