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

[Jason Gunthorpe]

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?

Thanks,
Jason