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Today, IOMMUFD also > supports No-IOMMU mode for group-based devices under vfio_compat mode. > However, IOMMUFD's native character device (cdev) does not yet support > No-IOMMU mode, which is the purpose of this patch. > > In summary, we have: > > |-------------------------+------+---------------| > | Device access mode | VFIO | IOMMUFD | > |-------------------------+------+---------------| > | group /dev/vfio/$GROUP | Yes | Yes | > |-------------------------+------+---------------| > | cdev /dev/vfio/devices/ | No | This patch | > |-------------------------+------+---------------| > > Beyond enabling cdev for IOMMUFD, this patch also addresses the following > deficiencies in the current No-IOMMU mode suggested by Jason[1]: > - Devices operating under No-IOMMU mode are limited to device-level UAPI > access, without container or IOAS-level capabilities. Consequently, > user-space drivers lack structured mechanisms for page pinning and often > resort to mlock(), which is less robust than pin_user_pages() used for > devices backed by a physical IOMMU. For example, mlock() does not prevent > page migration. > - There is no architectural mechanism for obtaining physical addresses for > DMA. As a workaround, user-space drivers frequently rely on /proc/pagemap > tricks or hardcoded values. > > By allowing noiommu device access to IOMMUFD IOAS and HWPT objects, this > patch brings No-IOMMU mode closer to full citizenship within the IOMMU > subsystem. In addition to addressing the two deficiencies mentioned above, > the expectation is that it will also enable No-IOMMU devices to seamlessly > participate in live update sessions via KHO [2]. > > Furthermore, these devices will use the IOMMUFD-based ownership checking model for > VFIO_DEVICE_PCI_HOT_RESET, eliminating the need for an iommufd_access object > as required in a previous attempt [3]. > > ChangeLog: > v10: > - Rebased to v7.2-rc2, no intended code change My impression is we are good on this now, right? I would like to pick it up? Jason