On Tue, Feb 18, 2025 at 03:22:06PM -0700, Alex Williamson wrote: > vfio-pci supports huge_fault for PCI MMIO BARs and will insert pud and > pmd mappings for well aligned mappings. follow_pfnmap_start() walks the > page table and therefore knows the page mask of the level where the > address is found and returns this through follow_pfnmap_args.pgmask. > Subsequent pfns from this address until the end of the mapping page are > necessarily consecutive. Use this information to retrieve a range of > pfnmap pfns in a single pass. > > With optimal mappings and alignment on systems with 1GB pud and 4KB > page size, this reduces iterations for DMA mapping PCI BARs by a > factor of 256K. In real world testing, the overhead of iterating > pfns for a VM DMA mapping a 32GB PCI BAR is reduced from ~1s to > sub-millisecond overhead. > > Signed-off-by: Alex Williamson <alex.williamson@xxxxxxxxxx> > --- > drivers/vfio/vfio_iommu_type1.c | 23 ++++++++++++++++------- > 1 file changed, 16 insertions(+), 7 deletions(-) Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx> Jason
