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

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Date:   Thu, 4 Aug 2022 02:03:46 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Baolu Lu <baolu.lu@...ux.intel.com>
CC:     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

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Thursday, August 4, 2022 3:03 AM
> 
> On Wed, Aug 03, 2022 at 09:07:35PM +0800, Baolu Lu wrote:
> > +/**
> > + * iommu_device_claim_pasid_owner() - Set ownership of a pasid on
> device
> > + * @dev: the device.
> > + * @pasid: the pasid of the device.
> > + * @owner: caller specified pointer. Used for exclusive ownership.
> > + *
> > + * Return 0 if it is allowed, otherwise an error.
> > + */
> > +int iommu_device_claim_pasid_owner(struct device *dev, ioasid_t pasid,
> void
> > *owner)
> 
> I don't see a use case for a special "pasid owner"
> 
> PASID is no different from normal DMA. If the calling driver already
> has the proper ownership of the device/group then it is fine for that
> driver to use any kind of IOMMU attachment, RID, PASID, whatever. It
> doesn't matter *how* the attachment is made.
> 

and pasid already has an alloc/free interface which already implies
an ownership model.