IB/mlx5: Maintain a single emergency page

The mlx5 driver needs to be able to issue invalidation to ODP MRs
even if it cannot allocate memory. To this end it preallocates
emergency pages to use when the situation arises.

This flow should be extremely rare enough, that we don't need
to worry about contention and therefore a single emergency page
is good enough.

Signed-off-by: Ilya Lesokhin <ilyal@mellanox.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/mlx5/mlx5_ib.h

@@ -130,9 +130,6 @@ struct mlx5_ib_ucontext {
 	/* protect vma_private_list add/del */
 	struct mutex		vma_private_list_mutex;
 
-	unsigned long		upd_xlt_page;
-	/* protect ODP/KSM */
-	struct mutex		upd_xlt_page_mutex;
 	u64			lib_caps;
 };
 
@@ -1220,4 +1217,7 @@ static inline int get_num_static_uars(struct mlx5_ib_dev *dev,
 	return get_uars_per_sys_page(dev, bfregi->lib_uar_4k) * bfregi->num_static_sys_pages;
 }
 
+unsigned long mlx5_ib_get_xlt_emergency_page(void);
+void mlx5_ib_put_xlt_emergency_page(void);
+
 #endif /* MLX5_IB_H */