vdpa/mlx5: Support creating resources with uid == 0

Currently all resources must be created with uid != 0 which is essential
when userspace processes are allocating virtquueue resources. Since this
is a kernel implementation, it is perfectly legal to open resources with
uid == 0.

In case firmware supports, avoid allocating user context.
Signed-off-by: Eli Cohen <elic@nvidia.com>
Link: https://lore.kernel.org/r/20210531160404.31368-1-elic@nvidia.comSigned-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>

drivers/vdpa/mlx5/core/resources.c

@@ -54,6 +54,9 @@ static int create_uctx(struct mlx5_vdpa_dev *mvdev, u16 *uid)
 	void *in;
 	int err;
 
+	if (MLX5_CAP_GEN(mvdev->mdev, umem_uid_0))
+		return 0;
+
 	/* 0 means not supported */
 	if (!MLX5_CAP_GEN(mvdev->mdev, log_max_uctx))
 		return -EOPNOTSUPP;
@@ -79,6 +82,9 @@ static void destroy_uctx(struct mlx5_vdpa_dev *mvdev, u32 uid)
 	u32 out[MLX5_ST_SZ_DW(destroy_uctx_out)] = {};
 	u32 in[MLX5_ST_SZ_DW(destroy_uctx_in)] = {};
 
+	if (!uid)
+		return;
+
 	MLX5_SET(destroy_uctx_in, in, opcode, MLX5_CMD_OP_DESTROY_UCTX);
 	MLX5_SET(destroy_uctx_in, in, uid, uid);
 

include/linux/mlx5/mlx5_ifc.h

@@ -1512,7 +1512,9 @@ struct mlx5_ifc_cmd_hca_cap_bits {
 	u8         uar_4k[0x1];
 	u8         reserved_at_241[0x9];
 	u8         uar_sz[0x6];
-	u8         reserved_at_250[0x8];
+	u8         reserved_at_248[0x2];
+	u8         umem_uid_0[0x1];
+	u8         reserved_at_250[0x5];
 	u8         log_pg_sz[0x8];
 
 	u8         bf[0x1];