RDMA/mlx5: Set mkeys for dmabuf at PAGE_SIZE

Set the mkey for dmabuf at PAGE_SIZE to support any SGL
after a move operation.

ib_umem_find_best_pgsz returns 0 on error, so it is
incorrect to check the returned page_size against PAGE_SIZE

Fixes: 90da7dc8 ("RDMA/mlx5: Support dma-buf based userspace memory region")
Signed-off-by: Chiara Meiohas <cmeiohas@nvidia.com>
Reviewed-by: Michael Guralnik <michaelgur@nvidia.com>
Link: https://lore.kernel.org/r/1e2289b9133e89f273a4e68d459057d032cbc2ce.1718301631.git.leon@kernel.orgSigned-off-by: Leon Romanovsky <leon@kernel.org>

drivers/infiniband/hw/mlx5/mlx5_ib.h

@@ -115,6 +115,19 @@ unsigned long __mlx5_umem_find_best_quantized_pgoff(
 		__mlx5_bit_sz(typ, page_offset_fld), 0, scale,                 \
 		page_offset_quantized)
 
+static inline unsigned long
+mlx5_umem_dmabuf_find_best_pgsz(struct ib_umem_dmabuf *umem_dmabuf)
+{
+	/*
+	 * mkeys used for dmabuf are fixed at PAGE_SIZE because we must be able
+	 * to hold any sgl after a move operation. Ideally the mkc page size
+	 * could be changed at runtime to be optimal, but right now the driver
+	 * cannot do that.
+	 */
+	return ib_umem_find_best_pgsz(&umem_dmabuf->umem, PAGE_SIZE,
+				      umem_dmabuf->umem.iova);
+}
+
 enum {
 	MLX5_IB_MMAP_OFFSET_START = 9,
 	MLX5_IB_MMAP_OFFSET_END = 255,

drivers/infiniband/hw/mlx5/odp.c

@@ -705,10 +705,8 @@ static int pagefault_dmabuf_mr(struct mlx5_ib_mr *mr, size_t bcnt,
 		return err;
 	}
 
-	page_size = mlx5_umem_find_best_pgsz(&umem_dmabuf->umem, mkc,
-					     log_page_size, 0,
-					     umem_dmabuf->umem.iova);
-	if (unlikely(page_size < PAGE_SIZE)) {
+	page_size = mlx5_umem_dmabuf_find_best_pgsz(umem_dmabuf);
+	if (!page_size) {
 		ib_umem_dmabuf_unmap_pages(umem_dmabuf);
 		err = -EINVAL;
 	} else {