Commit 099b59515499 ("Improve loading of multipage aligned buffers.")
modified bounce_bus_dmamap_load_buffer() with the assumption that busdma
memory allocations are physically contiguous, which is not always true:
bounce_bus_dmamem_alloc() will allocate memory with
kmem_alloc_attr_domainset() in some cases, and this function is not
guaranteed to return contiguous memory.
The damage seems to have been mitigated by clamping the segment size to
maxsegsz, but this was removed in commit a77e1f0f81df ("busdma: better
handling of small segment bouncing"); in practice, it seems busdma
memory is often allocated with maxsegsz == PAGE_SIZE. In particular,
after commit a77e1f0f81df I see occasional random kernel memory
corruption when benchmarking TCP through mlx5 interfaces.
Fix the problem by using separate flags for contiguous and
non-contiguous busdma memory allocations, and using that to decide
whether to clamp.
Fixes: 099b59515499 ("Improve loading of multipage aligned buffers.")
Fixes: a77e1f0f81df ("busdma: better handling of small segment bouncing")