IB/mlx5: Use the original address for the page during free_pages

The removal of 'buffer' in the patch below caused free_page() to use a
value that had been offset since the wqe pointer is adjusted while the
routine runs.

The current implementation of free_pages() rounds down to a pfn,
discarding the adjustment, but this is not the right way to use the
API. Preserve the initial value and use it for free_page().

Fixes: 0f51427bd0 ("RDMA/mlx5: Cleanup WQE page fault handler")
Link: https://lore.kernel.org/r/20190916064818.19823-2-leon@kernel.org
Signed-off-by: Danit Goldberg <danitg@mellanox.com>
Reviewed-by: Yishai Hadas <yishaih@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/mlx5/odp.c

@@ -1131,7 +1131,7 @@ static void mlx5_ib_mr_wqe_pfault_handler(struct mlx5_ib_dev *dev,
 {
 	bool sq = pfault->type & MLX5_PFAULT_REQUESTOR;
 	u16 wqe_index = pfault->wqe.wqe_index;
-	void *wqe = NULL, *wqe_end = NULL;
+	void *wqe, *wqe_start = NULL, *wqe_end = NULL;
 	u32 bytes_mapped, total_wqe_bytes;
 	struct mlx5_core_rsc_common *res;
 	int resume_with_error = 1;
@@ -1152,12 +1152,13 @@ static void mlx5_ib_mr_wqe_pfault_handler(struct mlx5_ib_dev *dev,
 		goto resolve_page_fault;
 	}
 
-	wqe = (void *)__get_free_page(GFP_KERNEL);
-	if (!wqe) {
+	wqe_start = (void *)__get_free_page(GFP_KERNEL);
+	if (!wqe_start) {
 		mlx5_ib_err(dev, "Error allocating memory for IO page fault handling.\n");
 		goto resolve_page_fault;
 	}
 
+	wqe = wqe_start;
 	qp = (res->res == MLX5_RES_QP) ? res_to_qp(res) : NULL;
 	if (qp && sq) {
 		ret = mlx5_ib_read_user_wqe_sq(qp, wqe_index, wqe, PAGE_SIZE,
@@ -1212,7 +1213,7 @@ resolve_page_fault:
 		    pfault->wqe.wq_num, resume_with_error,
 		    pfault->type);
 	mlx5_core_res_put(res);
-	free_page((unsigned long)wqe);
+	free_page((unsigned long)wqe_start);
 }
 
 static int pages_in_range(u64 address, u32 length)