linux-kernel - Re: [RFC v2] /dev/iommu uAPI proposal

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Date:   Tue, 13 Jul 2021 20:22:44 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        David Gibson <david@...son.dropbear.id.au>,
        Jason Wang <jasowang@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "Enrico Weigelt, metux IT consult" <lkml@...ux.net>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shenming Lu <lushenming@...wei.com>,
        Joerg Roedel <joro@...tes.org>,
        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>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        David Woodhouse <dwmw2@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>
Subject: Re: [RFC v2] /dev/iommu uAPI proposal

On Tue, Jul 13, 2021 at 11:20:12PM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Wednesday, July 14, 2021 7:03 AM
> > 
> > On Tue, Jul 13, 2021 at 10:48:38PM +0000, Tian, Kevin wrote:
> > 
> > > We can still bind to the parent with cookie, but with
> > > iommu_register_ sw_device() IOMMU fd knows that this binding doesn't
> > > need to establish any security context via IOMMU API.
> > 
> > AFAIK there is no reason to involve the parent PCI or other device in
> > SW mode. The iommufd doesn't need to be aware of anything there.
> > 
> 
> Yes. but does it makes sense to have an unified model in IOMMU fd
> which always have a [struct device, cookie] with flags to indicate whether 
> the binding/attaching should be specially handled for sw mdev? Or
> are you suggesting that lacking of struct device is actually the indicator
> for such trick?

I think you've veered into such micro implementation details that it
is better to wait and see how things look.

The important point here is that whatever physical device is under a
SW mdev does not need to be passed to the iommufd because there is
nothing it can do with that information.

Jason