linux-kernel - RE: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

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Date:   Sat, 8 May 2021 05:46:09 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Alex Williamson <alex.williamson@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Auger Eric <eric.auger@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>
Subject: RE: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation
 APIs

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Thursday, April 29, 2021 4:46 AM
> 
> > > I think the name IOASID is fine for the uAPI, the kernel version can
> > > be called ioasid_id or something.
> >
> > ioasid is already an id and then ioasid_id just adds confusion. Another
> > point is that ioasid is currently used to represent both PCI PASID and
> > ARM substream ID in the kernel. It implies that if we want to separate
> > ioasid and pasid in the uAPI the 'pasid' also needs to be replaced with
> > another general term usable for substream ID. Are we making the
> > terms too confusing here?
> 
> This is why I also am not so sure about exposing the PASID in the API
> because it is ultimately a HW specific item.
> 
> As I said to David, one avenue is to have some generic uAPI that is
> very general and keep all this deeply detailed stuff, that really only
> matters for qemu, as part of a more HW specific vIOMMU driver
> interface.
> 

OK, so the general uAPI will not expose hw_id and just provide everything
generic for managing I/O page table (map/unmap, nesting, etc.) through 
IOASID and then specific uAPI is provided to handle platform specific
requirements (hw_id, iova windows, etc.)

Thanks
Kevin