Re: [Intel-gfx] [PATCH v15 00/26] Add vfio_device cdev for iommufd support

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 24 Jul 2023 13:09:22 -0600
Alex Williamson <alex.williamson@redhat.com> wrote:

> On Tue, 18 Jul 2023 13:57:46 -0300
> Jason Gunthorpe <jgg@nvidia.com> wrote:
> 
> > On Tue, Jul 18, 2023 at 06:55:25AM -0700, Yi Liu wrote:  
> > > Existing VFIO provides group-centric user APIs for userspace. Userspace
> > > opens the /dev/vfio/$group_id first before getting device fd and hence
> > > getting access to device. This is not the desired model for iommufd. Per
> > > the conclusion of community discussion[1], iommufd provides device-centric
> > > kAPIs and requires its consumer (like VFIO) to be device-centric user
> > > APIs. Such user APIs are used to associate device with iommufd and also
> > > the I/O address spaces managed by the iommufd.
> > > 
> > > This series first introduces a per device file structure to be prepared
> > > for further enhancement and refactors the kvm-vfio code to be prepared
> > > for accepting device file from userspace. After this, adds a mechanism for
> > > blocking device access before iommufd bind. Then refactors the vfio to be
> > > able to handle cdev paths (e.g. iommufd binding, no-iommufd, [de]attach ioas).
> > > This refactor includes making the device_open exclusive between the group
> > > and the cdev path, only allow single device open in cdev path; vfio-iommufd
> > > code is also refactored to support cdev. e.g. split the vfio_iommufd_bind()
> > > into two steps. Eventually, adds the cdev support for vfio device and the
> > > new ioctls, then makes group infrastructure optional as it is not needed
> > > when vfio device cdev is compiled.
> > > 
> > > This series is based on some preparation works done to vfio emulated devices[2]
> > > and vfio pci hot reset enhancements[3]. Per discussion[4], this series does not
> > > support cdev for physical devices that do not have IOMMU. Such devices only
> > > have group-centric user APIs.
> > > 
> > > This series is a prerequisite for iommu nesting for vfio device[5] [6].
> > > 
> > > The complete code can be found in below branch, simple tests done to the
> > > legacy group path and the cdev path. QEMU changes are in upstreaming[7]
> > > and the complete code can be found at[8]
> > > 
> > > https://github.com/yiliu1765/iommufd/tree/vfio_device_cdev_v15
> > > (config CONFIG_IOMMUFD=y CONFIG_VFIO_DEVICE_CDEV=y)    
> > 
> > Alex, if you are still good with this lets make this into a shared
> > branch, do you want to do it or would you like a PR from me?  
> 
> Sorry, was out much of last week.  Yes, my intent would be to put this
> both in a shared branch and my next branch for v6.6.  Given this is
> mostly vfio, it seems like it'd make sense for me to provide that
> branch but I may not get to it until tomorrow.  Thanks,

Both series are applied to my next branch for v6.6 and I've also
published them to the v6.6/vfio/cdev branch[1].  Thanks for all the
work and collaboration on this effort!

Alex

[1]https://github.com/awilliam/linux-vfio/tree/v6.6/vfio/cdev