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

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Date:   Thu, 3 Jun 2021 09:49:23 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     David Gibson <david@...son.dropbear.id.au>,
        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>,
        "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>,
        Kirti Wankhede <kwankhede@...dia.com>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [RFC] /dev/ioasid uAPI proposal

On Thu, Jun 03, 2021 at 07:17:23AM +0000, Tian, Kevin wrote:
> > From: David Gibson <david@...son.dropbear.id.au>
> > Sent: Wednesday, June 2, 2021 2:15 PM
> > 
> [...] 
> > > An I/O address space takes effect in the IOMMU only after it is attached
> > > to a device. The device in the /dev/ioasid context always refers to a
> > > physical one or 'pdev' (PF or VF).
> > 
> > What you mean by "physical" device here isn't really clear - VFs
> > aren't really physical devices, and the PF/VF terminology also doesn't
> > extent to non-PCI devices (which I think we want to consider for the
> > API, even if we're not implemenenting it any time soon).
> 
> Yes, it's not very clear, and more in PCI context to simplify the 
> description. A "physical" one here means an PCI endpoint function
> which has a unique RID. It's more to differentiate with later mdev/
> subdevice which uses both RID+PASID. Naming is always a hard
> exercise to me... Possibly I'll just use device vs. subdevice in future
> versions.

Using PCI words:

A "physical" device is RID matching.

A "subdevice" is (RID, PASID) matching.

A "SW mdev" is performing DMA isolation in a device specific way - all
DMA's from the device are routed to the hypervisor's IOMMU page
tables.

Jason