On Tue, Sep 01, 2020 at 09:43:30PM -0300, Jason Gunthorpe wrote:
> rdma_for_each_block() makes assumptions about how the SGL is constructed
> that don't work if the block size is below the page size used to to build
> the SGL.
>
> The rules for umem SGL construction require that the SG's all be PAGE_SIZE
> aligned and we don't encode the actual byte offset of the VA range inside
> the SGL using offset and length. So rdma_for_each_block() has no idea
> where the actual starting/ending point is to compute the first/last block
> boundary if the starting address should be within a SGL.
>
> Fixing the SGL construction turns out to be really hard, and will be the
> subject of other patches. For now block smaller pages.
>
> 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 | 6 ++++++
> 1 file changed, 6 insertions(+)
>
> diff --git a/drivers/infiniband/core/umem.c b/drivers/infiniband/core/umem.c
> index 120e98403c345d..7b5bc969e55630 100644
> --- a/drivers/infiniband/core/umem.c
> +++ b/drivers/infiniband/core/umem.c
> @@ -151,6 +151,12 @@ unsigned long ib_umem_find_best_pgsz(struct ib_umem *umem,
> dma_addr_t mask;
> int i;
>
> + /* rdma_for_each_block() has a bug if the page size is smaller than the
> + * page size used to build the umem. For now prevent smaller page sizes
> + * from being returned.
> + */
> + pgsz_bitmap &= GENMASK(BITS_PER_LONG - 1, PAGE_SHIFT);
> +
Why do we care about such case? Why can't we leave this check forever?
Thanks,
Reviewed-by: Leon Romanovsky <leonro@xxxxxxxxxx>
