On Tue, Sep 01, 2020 at 09:43:29PM -0300, Jason Gunthorpe wrote:
> 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")
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
> ---
> drivers/infiniband/core/umem.c | 10 ++++++++--
> 1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index 831bff8d52e547..120e98403c345d 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -156,8 +156,14 @@ 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 + umem->address) ^
> + umem->address));
The use of umem->address is incorrect here as well, it should be virt.
All places on the DMA side that touch address are wrong..
Jason
