Commit a40c20da authored by Jason Gunthorpe's avatar Jason Gunthorpe
Browse files

RDMA/umem: Fix ib_umem_find_best_pgsz() for mappings that cross a page boundary 

It is possible for a single SGL to span an aligned boundary, eg if the SGL
is

  61440 -> 90112

Then the length is 28672, which currently limits the block size to
32k. With a 32k page size the two covering blocks will be:

  32768->65536 and 65536->98304

However, the correct answer is a 128K block size which will span the whole
28672 bytes in a single block.

Instead of limiting based on length figure out which high IOVA bits don't
change between the start and end addresses. That is the highest useful
page size.

Fixes: 4a353399 ("RDMA/umem: Add API to find best driver supported page size in an MR")
Link: https://lore.kernel.org/r/1-v2-270386b7e60b+28f4-umem_1_jgg@nvidia.com


Reviewed-by: default avatarLeon Romanovsky <leonro@nvidia.com>
Reviewed-by: default avatarShiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: default avatarJason Gunthorpe <jgg@nvidia.com>
parent 71ff3f62

drivers/infiniband/core/umem.c

+7 −2
Original line number Diff line number Diff line
@@ -156,8 +156,13 @@ unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem, 
		return 0;



	va = virt;

	/* max page size not to exceed MR length */

	mask = roundup_pow_of_two(umem->length);

	/* The best result is the smallest page size that results in the minimum

	 * number of required pages. Compute the largest page size that could

	 * work based on VA address bits that don't change.

	 */

	mask = pgsz_bitmap &

	       GENMASK(BITS_PER_LONG - 1,

		       bits_per((umem->length - 1 + virt) ^ virt));

	/* offset into first SGL */

	pgoff = umem->address & ~PAGE_MASK;