linux-kernel - Re: [RFC 7/7] vfio: Add vfio_register_pasid_iommu

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Date:   Thu, 9 Nov 2023 16:20:03 +0800
From:   Yi Liu <yi.l.liu@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>
CC:     "cohuck@...hat.com" <cohuck@...hat.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "mjrosato@...ux.ibm.com" <mjrosato@...ux.ibm.com>,
        "chao.p.peng@...ux.intel.com" <chao.p.peng@...ux.intel.com>,
        "yi.y.sun@...ux.intel.com" <yi.y.sun@...ux.intel.com>,
        "peterx@...hat.com" <peterx@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "shameerali.kolothum.thodi@...wei.com" 
        <shameerali.kolothum.thodi@...wei.com>,
        "lulu@...hat.com" <lulu@...hat.com>,
        "suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>,
        "Duan, Zhenzhong" <zhenzhong.duan@...el.com>,
        "Martins, Joao" <joao.m.martins@...cle.com>
Subject: Re: [RFC 7/7] vfio: Add vfio_register_pasid_iommu_dev()

On 2023/10/10 16:33, Tian, Kevin wrote:
>> From: Liu, Yi L <yi.l.liu@...el.com>
>> Sent: Monday, October 9, 2023 4:51 PM
>>
>> From: Kevin Tian <kevin.tian@...el.com>
>>
>> This adds vfio_register_pasid_iommu_dev() for device driver to register
>> virtual devices which are isolated per PASID in physical IOMMU. The major
>> usage is for the SIOV devices which allows device driver to tag the DMAs
>> out of virtual devices within it with different PASIDs.
>>
>> For a given vfio device, VFIO core creates both group user interface and
>> device user interface (device cdev) if configured. However, for the virtual
>> devices backed by PASID of the device, VFIO core shall only create device
>> user interface as there is no plan to support such devices in the legacy
>> vfio_iommu drivers which is a must if creating group user interface for
>> such virtual devices. This introduces a VFIO_PASID_IOMMU group type for
>> the device driver to register PASID virtual devices, and provides a wrapper
>> API for it. In particular no iommu group (neither fake group or real group)
>> exists per PASID, hence no group interface for this type.
>>
> 
> this commit msg needs some revision. The key is that there is no group
> per pasid *in concept* so it doesn't make sense to fake a group...

how about below?

This adds vfio_register_pasid_iommu_dev() for device driver to register
virtual devices which are isolated per PASID in physical IOMMU. The major
usage is for the SIOV devices which allows the device driver to tag the
DMAs out of virtual devices within it with different PASIDs.

For the PASID virtual devices, there is no iommu group in concept. Hence
the VFIO core only creates device user interface for such devices. This
introduces a VFIO_PASID_IOMMU group type to differentiate from the other
devices that have iommu group in concept.

-- 
Regards,
Yi Liu