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

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Message-ID: <MWHPR11MB18866CDB2F82A2E9285994998C519@MWHPR11MB1886.namprd11.prod.outlook.com>
Date:   Thu, 13 May 2021 06:52:43 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     David Gibson <david@...son.dropbear.id.au>,
        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>,
        "Alexey Kardashevskiy" <aik@...abs.ru>
Subject: RE: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation
 APIs

> From: David Gibson <david@...son.dropbear.id.au>
> Sent: Thursday, May 13, 2021 2:01 PM
> >
> > But this definitely all becomes HW specific.
> >
> > For instance I want to have an ARM vIOMMU driver it needs to do some
> >
> >  ret = ioctl(ioasid_fd, CREATE_NESTED_IOASID, [page table format is
> ARMvXXX])
> >  if (ret == -EOPNOTSUPP)
> >      ret = ioctl(ioasid_fd, CREATE_NORMAL_IOASID, ..)
> >      // and do completely different and more expensive emulation
> >
> > I can get a little bit of generality, but at the end of the day the
> > IOMMU must create a specific HW layout of the nested page table, if it
> > can't, it can't.
> 
> Erm.. I don't really know how your IOASID interface works here.  I'm
> thinking about the VFIO interface where maps and unmaps are via
> explicit ioctl()s, which provides an obvious point to do translation
> between page table formats.
> 

We are working on a draft uAPI proposal based on the discussions in this
thread. expect to send it out next week. 

Thanks
Kevin