linux-kernel - RE: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND

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Date:   Wed, 29 Sep 2021 22:34:29 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     David Gibson <david@...son.dropbear.id.au>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "hch@....de" <hch@....de>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "jean-philippe@...aro.org" <jean-philippe@...aro.org>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "lkml@...ux.net" <lkml@...ux.net>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "lushenming@...wei.com" <lushenming@...wei.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "corbet@....net" <corbet@....net>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "Tian, Jun J" <jun.j.tian@...el.com>, "Wu, Hao" <hao.wu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "nicolinc@...dia.com" <nicolinc@...dia.com>
Subject: RE: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND_IOMMUFD

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, September 29, 2021 8:28 PM
> 
> On Wed, Sep 29, 2021 at 06:41:00AM +0000, Tian, Kevin wrote:
> > > From: David Gibson <david@...son.dropbear.id.au>
> > > Sent: Wednesday, September 29, 2021 2:01 PM
> > >
> > > On Sun, Sep 19, 2021 at 02:38:36PM +0800, Liu Yi L wrote:
> > > > This patch adds VFIO_DEVICE_BIND_IOMMUFD for userspace to bind
> the
> > > vfio
> > > > device to an iommufd. No VFIO_DEVICE_UNBIND_IOMMUFD interface
> is
> > > provided
> > > > because it's implicitly done when the device fd is closed.
> > > >
> > > > In concept a vfio device can be bound to multiple iommufds, each
> hosting
> > > > a subset of I/O address spaces attached by this device.
> > >
> > > I really feel like this many<->many mapping between devices is going
> > > to be super-confusing, and therefore make it really hard to be
> > > confident we have all the rules right for proper isolation.
> >
> > Based on new discussion on group ownership part (patch06), I feel this
> > many<->many relationship will disappear. The context fd (either container
> > or iommufd) will uniquely mark the ownership on a physical device and
> > its group. With this design it's impractical to have one device bound
> > to multiple iommufds.
> 
> That should be a requirement! We have no way to prove that two
> iommufds are the same security domain, so devices/groups cannot be
> shared.
> 
> That is why the API I suggested takes in a struct file to ID the user
> security context. A group is accessible only from that single struct
> file and no more.
> 
> If the first series goes the way I outlined then I think David's
> concern about security is strongly solved as the IOMMU layer is
> directly managing it with a very clear responsiblity and semantic.
> 

Yes, this is also my understanding now.