RDMA/mlx5: Fix handling of IOVA != user_va in ODP paths

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>

drivers/infiniband/hw/mlx5/mr.c

@@ -1246,6 +1246,8 @@ struct ib_mr *mlx5_ib_reg_user_mr(struct ib_pd *pd, u64 start, u64 length,
 
 	if (IS_ENABLED(CONFIG_INFINIBAND_ON_DEMAND_PAGING) && !start &&
 	    length == U64_MAX) {
+		if (virt_addr != start)
+			return ERR_PTR(-EINVAL);
 		if (!(access_flags & IB_ACCESS_ON_DEMAND) ||
 		    !(dev->odp_caps.general_caps & IB_ODP_SUPPORT_IMPLICIT))
 			return ERR_PTR(-EINVAL);

drivers/infiniband/hw/mlx5/odp.c

@@ -624,11 +624,10 @@ static int pagefault_real_mr(struct mlx5_ib_mr *mr, struct ib_umem_odp *odp,
 	bool downgrade = flags & MLX5_PF_FLAGS_DOWNGRADE;
 	unsigned long current_seq;
 	u64 access_mask;
-	u64 start_idx, page_mask;
+	u64 start_idx;
 
 	page_shift = odp->page_shift;
-	page_mask = ~(BIT(page_shift) - 1);
-	start_idx = (user_va - (mr->mmkey.iova & page_mask)) >> page_shift;
+	start_idx = (user_va - ib_umem_start(odp)) >> page_shift;
 	access_mask = ODP_READ_ALLOWED_BIT;
 
 	if (odp->umem.writable && !downgrade)
@@ -767,11 +766,19 @@ static int pagefault_mr(struct mlx5_ib_mr *mr, u64 io_virt, size_t bcnt,
 {
 	struct ib_umem_odp *odp = to_ib_umem_odp(mr->umem);
 
+	if (unlikely(io_virt < mr->mmkey.iova))
+		return -EFAULT;
+
 	if (!odp->is_implicit_odp) {
-		if (unlikely(io_virt < ib_umem_start(odp) ||
-			     ib_umem_end(odp) - io_virt < bcnt))
+		u64 user_va;
+
+		if (check_add_overflow(io_virt - mr->mmkey.iova,
+				       (u64)odp->umem.address, &user_va))
+			return -EFAULT;
+		if (unlikely(user_va >= ib_umem_end(odp) ||
+			     ib_umem_end(odp) - user_va < bcnt))
 			return -EFAULT;
-		return pagefault_real_mr(mr, odp, io_virt, bcnt, bytes_mapped,
+		return pagefault_real_mr(mr, odp, user_va, bcnt, bytes_mapped,
 					 flags);
 	}
 	return pagefault_implicit_mr(mr, odp, io_virt, bcnt, bytes_mapped,