linux-kernel - Re: [RFC] /dev/ioasid uAPI proposal

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Message-ID: <20210601172652.GK1002214@nvidia.com>
Date:   Tue, 1 Jun 2021 14:26:52 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Alex Williamson (alex.williamson@...hat.com)" 
        <alex.williamson@...hat.com>, Jason Wang <jasowang@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Tue, Jun 01, 2021 at 07:09:21PM +0800, Lu Baolu wrote:

> This version only covers 1) and 4). Do you think we need to support 2),
> 3) and beyond? 

Yes aboslutely. The API should be flexable enough to specify the
creation of all future page table formats we'd want to have and all HW
specific details on those formats.

> If so, it seems that we need some in-kernel helpers and uAPIs to
> support pre-installing a page table to IOASID. 

Not sure what this means..

> From this point of view an IOASID is actually not just a variant of
> iommu_domain, but an I/O page table representation in a broader
> sense.

Yes, and things need to evolve in a staged way. The ioctl API should
have room for this growth but you need to start out with some
constrained enough to actually implement then figure out how to grow
from there

Jason