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

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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: 4a35339958f1 ("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: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Shiraz Saleem <shiraz.saleem@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
This commit is contained in:
Jason Gunthorpe 2020-09-04 19:41:42 -03:00
parent 71ff3f6268
commit a40c20dabd
1 changed files with 7 additions and 2 deletions
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9
drivers/infiniband/core/umem.c
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@ -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;