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Documentation/userspace-api/iommufd.rst
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Merge patch series "IOMMUFD Generic interface"
Jason Gunthorpe <jgg@nvidia.com> says: ================== iommufd is the user API to control the IOMMU subsystem as it relates to managing IO page tables that point at user space memory. It takes over from drivers/vfio/vfio_iommu_type1.c (aka the VFIO container) which is the VFIO specific interface for a similar idea. We see a broad need for extended features, some being highly IOMMU device specific: - Binding iommu_domain's to PASID/SSID - Userspace IO page tables, for ARM, x86 and S390 - Kernel bypassed invalidation of user page tables - Re-use of the KVM page table in the IOMMU - Dirty page tracking in the IOMMU - Runtime Increase/Decrease of IOPTE size - PRI support with faults resolved in userspace Many of these HW features exist to support VM use cases - for instance the combination of PASID, PRI and Userspace IO Page Tables allows an implementation of DMA Shared Virtual Addressing (vSVA) within a guest. Dirty tracking enables VM live migration with SRIOV devices and PASID support allow creating "scalable IOV" devices, among other things. As these features are fundamental to a VM platform they need to be uniformly exposed to all the driver families that do DMA into VMs, which is currently VFIO and VDPA. The pre-v1 series proposed re-using the VFIO type 1 data structure, however it was suggested that if we are doing this big update then we should also come with an improved data structure that solves the limitations that VFIO type1 has. Notably this addresses: - Multiple IOAS/'containers' and multiple domains inside a single FD - Single-pin operation no matter how many domains and containers use a page - A fine grained locking scheme supporting user managed concurrency for multi-threaded map/unmap - A pre-registration mechanism to optimize vIOMMU use cases by pre-pinning pages - Extended ioctl API that can manage these new objects and exposes domains directly to user space - domains are sharable between subsystems, eg VFIO and VDPA The bulk of this code is a new data structure design to track how the IOVAs are mapped to PFNs. iommufd intends to be general and consumable by any driver that wants to DMA to userspace. From a driver perspective it can largely be dropped in in-place of iommu_attach_device() and provides a uniform full feature set to all consumers. As this is a larger project this series is the first step. This series provides the iommfd "generic interface" which is designed to be suitable for applications like DPDK and VMM flows that are not optimized to specific HW scenarios. It is close to being a drop in replacement for the existing VFIO type 1 and supports existing qemu based VM flows. Several follow-on series are being prepared: - Patches integrating with qemu in native mode: https://github.com/yiliu1765/qemu/commits/qemu-iommufd-6.0-rc2 - A completed integration with VFIO now exists that covers "emulated" mdev use cases now, and can pass testing with qemu/etc in compatability mode: https://github.com/jgunthorpe/linux/commits/vfio_iommufd - A draft providing system iommu dirty tracking on top of iommufd, including iommu driver implementations: https://github.com/jpemartins/linux/commits/x86-iommufd This pairs with patches for providing a similar API to support VFIO-device tracking to give a complete vfio solution: https://lore.kernel.org/kvm/20220901093853.60194-1-yishaih@nvidia.com/ - Userspace page tables aka 'nested translation' for ARM and Intel iommu drivers: https://github.com/nicolinc/iommufd/commits/iommufd_nesting - "device centric" vfio series to expose the vfio_device FD directly as a normal cdev, and provide an extended API allowing dynamically changing the IOAS binding: https://github.com/yiliu1765/iommufd/commits/iommufd-v6.0-rc2-nesting-0901 - Drafts for PASID and PRI interfaces are included above as well Overall enough work is done now to show the merit of the new API design and at least draft solutions to many of the main problems. Several people have contributed directly to this work: Eric Auger, Joao Martins, Kevin Tian, Lu Baolu, Nicolin Chen, Yi L Liu. Many more have participated in the discussions that lead here, and provided ideas. Thanks to all! The v1/v2 iommufd series has been used to guide a large amount of preparatory work that has now been merged. The general theme is to organize things in a way that makes injecting iommufd natural: - VFIO live migration support with mlx5 and hisi_acc drivers. These series need a dirty tracking solution to be really usable. https://lore.kernel.org/kvm/20220224142024.147653-1-yishaih@nvidia.com/ https://lore.kernel.org/kvm/20220308184902.2242-1-shameerali.kolothum.thodi@huawei.com/ - Significantly rework the VFIO gvt mdev and remove struct mdev_parent_ops https://lore.kernel.org/lkml/20220411141403.86980-1-hch@lst.de/ - Rework how PCIe no-snoop blocking works https://lore.kernel.org/kvm/0-v3-2cf356649677+a32-intel_no_snoop_jgg@nvidia.com/ - Consolidate dma ownership into the iommu core code https://lore.kernel.org/linux-iommu/20220418005000.897664-1-baolu.lu@linux.intel.com/ - Make all vfio driver interfaces use struct vfio_device consistently https://lore.kernel.org/kvm/0-v4-8045e76bf00b+13d-vfio_mdev_no_group_jgg@nvidia.com/ - Remove the vfio_group from the kvm/vfio interface https://lore.kernel.org/kvm/0-v3-f7729924a7ea+25e33-vfio_kvm_no_group_jgg@nvidia.com/ - Simplify locking in vfio https://lore.kernel.org/kvm/0-v2-d035a1842d81+1bf-vfio_group_locking_jgg@nvidia.com/ - Remove the vfio notifiter scheme that faces drivers https://lore.kernel.org/kvm/0-v4-681e038e30fd+78-vfio_unmap_notif_jgg@nvidia.com/ - Improve the driver facing API for vfio pin/unpin pages to make the presence of struct page clear https://lore.kernel.org/kvm/20220723020256.30081-1-nicolinc@nvidia.com/ - Clean up in the Intel IOMMU driver https://lore.kernel.org/linux-iommu/20220301020159.633356-1-baolu.lu@linux.intel.com/ https://lore.kernel.org/linux-iommu/20220510023407.2759143-1-baolu.lu@linux.intel.com/ https://lore.kernel.org/linux-iommu/20220514014322.2927339-1-baolu.lu@linux.intel.com/ https://lore.kernel.org/linux-iommu/20220706025524.2904370-1-baolu.lu@linux.intel.com/ https://lore.kernel.org/linux-iommu/20220702015610.2849494-1-baolu.lu@linux.intel.com/ - Rework s390 vfio drivers https://lore.kernel.org/kvm/20220707135737.720765-1-farman@linux.ibm.com/ - Normalize vfio ioctl handling https://lore.kernel.org/kvm/0-v2-0f9e632d54fb+d6-vfio_ioctl_split_jgg@nvidia.com/ - VFIO API for dirty tracking (aka dma logging) managed inside a PCI device, with mlx5 implementation https://lore.kernel.org/kvm/20220901093853.60194-1-yishaih@nvidia.com - Introduce a struct device sysfs presence for struct vfio_device https://lore.kernel.org/kvm/20220901143747.32858-1-kevin.tian@intel.com/ - Complete restructuring the vfio mdev model https://lore.kernel.org/kvm/20220822062208.152745-1-hch@lst.de/ - Isolate VFIO container code in preperation for iommufd to provide an alternative implementation of it all https://lore.kernel.org/kvm/0-v1-a805b607f1fb+17b-vfio_container_split_jgg@nvidia.com - Simplify and consolidate iommu_domain/device compatability checking https://lore.kernel.org/linux-iommu/cover.1666042872.git.nicolinc@nvidia.com/ - Align iommu SVA support with the domain-centric model https://lore.kernel.org/all/20221031005917.45690-1-baolu.lu@linux.intel.com/ This is about 233 patches applied since March, thank you to everyone involved in all this work! Currently there are a number of supporting series still in progress: - DMABUF exporter support for VFIO to allow PCI P2P with VFIO https://lore.kernel.org/r/0-v2-472615b3877e+28f7-vfio_dma_buf_jgg@nvidia.com - Start to provide iommu_domain ops for POWER https://lore.kernel.org/all/20220714081822.3717693-1-aik@ozlabs.ru/ However, these are not necessary for this series to advance. Syzkaller coverage has been merged and is now running in the syzbot environment on linux-next: https://github.com/google/syzkaller/pull/3515 https://github.com/google/syzkaller/pull/3521 ================== Link: https://lore.kernel.org/r/0-v6-a196d26f289e+11787-iommufd_jgg@nvidia.com Signed-off-by:Jason Gunthorpe <jgg@nvidia.com>