vfio: Add an IOVA bitmap support

2022-09-08T18:59:00+00:00

The new facility adds a bunch of wrappers that abstract how an IOVA range is represented in a bitmap that is granulated by a given page_size. So it translates all the lifting of dealing with user pointers into its corresponding kernel addresses backing said user memory into doing finally the (non-atomic) bitmap ops to change various bits. The formula for the bitmap is: data[(iova / page_size) / 64] & (1ULL << (iova % 64)) Where 64 is the number of bits in a unsigned long (depending on arch) It introduces an IOVA iterator that uses a windowing scheme to minimize the pinning overhead, as opposed to pinning it on demand 4K at a time. Assuming a 4K kernel page and 4K requested page size, we can use a single kernel page to hold 512 page pointers, mapping 2M of bitmap, representing 64G of IOVA space. An example usage of these helpers for a given @base_iova, @page_size, @length and __user @data: bitmap = iova_bitmap_alloc(base_iova, page_size, length, data); if (IS_ERR(bitmap)) return -ENOMEM; ret = iova_bitmap_for_each(bitmap, arg, dirty_reporter_fn); iova_bitmap_free(bitmap); Each iteration of the @dirty_reporter_fn is called with a unique @iova and @length argument, indicating the current range available through the iova_bitmap. The @dirty_reporter_fn uses iova_bitmap_set() to mark dirty areas (@iova_length) within that provided range, as following: iova_bitmap_set(bitmap, iova, iova_length); The facility is intended to be used for user bitmaps representing dirtied IOVAs by IOMMU (via IOMMUFD) and PCI Devices (via vfio-pci). Signed-off-by: Joao Martins Signed-off-by: Yishai Hadas Link: https://lore.kernel.org/r/20220908183448.195262-5-yishaih@nvidia.com Signed-off-by: Alex Williamson

kernel/linux.git/include/linux/iova_bitmap.h, branch v6.6.132

vfio: Add an IOVA bitmap support