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

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Date:   Tue, 13 Jul 2021 13:32:49 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Alex Williamson <alex.williamson@...hat.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.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 10:26:07AM -0600, Alex Williamson wrote:
> Quoting this proposal again:
> 
> > 1)  A successful binding call for the first device in the group creates 
> >     the security context for the entire group, by:
> > 
> >     * Verifying group viability in a similar way as VFIO does;
> > 
> >     * Calling IOMMU-API to move the group into a block-dma state,
> >       which makes all devices in the group attached to an block-dma
> >       domain with an empty I/O page table;
> > 
> >     VFIO should not allow the user to mmap the MMIO bar of the bound
> >     device until the binding call succeeds.
> 
> The attach step is irrelevant to my question, the bind step is where
> the device/group gets into a secure state for device access.

Binding is similar to attach, it will need to indicate the drivers
intention and a SW driver will not attach to the PCI device underneath
it.

> AIUI the operation of VFIO_DEVICE_BIND_IOMMU_FD looks like this:
> 
> 	iommu_ctx = iommu_ctx_fdget(iommu_fd);
> 
> 	mdev = mdev_from_dev(vdev->dev);
> 	dev = mdev ? mdev_parent_dev(mdev) : vdev->dev;
> 
> 	iommu_dev = iommu_register_device(iommu_ctx, dev, cookie);

A default of binding to vdev->dev might turn out to be OK, but this
needs to be an overridable op in vfio_device and the SW mdevs will
have to do some 'iommu_register_sw_device()' and not pass in a dev at
all.

Jason