Till recently it was not possible for userspace to specify a different
IOVA, but with the new ibv_reg_mr_iova() library call this can be done.

To compute the user_va we must compute:
  user_va = (iova - iova_start) + user_va_start

while being cautious of overflow and other math problems.

The iova is not reliably stored in the mmkey when the MR is created. Only
the cached creation path (the common one) set it, so it must also be set
when creating uncached MRs.

Fix the weird use of iova when computing the starting page index in the
MR. In the normal case, when iova == umem.address:
  iova & (~(BIT(page_shift) - 1)) ==
  ALIGN_DOWN(umem.address, odp->page_size) ==
  ib_umem_start(odp)

And when iova is different using it in math with a user_va is wrong.

Finally, do not allow an implicit ODP to be created with a non-zero IOVA
as we have no support for that.

Fixes: 7bdf65d4 ("IB/mlx5: Handle page faults")
Signed-off-by: Moni Shoua <monis@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>