On Tue, 28 Jan 2020, Kees Cook wrote:

quoted

On the other hand not marking the DMA caches still seems questionable.

My understanding is that exposing DMA memory to userspace copies can
lead to unexpected results, especially for misbehaving hardware, so I'm
not convinced this is a generically bad hardening choice.

"DMA" memory (and thus DMA caches) have nothing to do with DMA. Its a
legacy term. "DMA Memory" is memory limited to a certain
physical address boundary (old restrictions on certain devices only
supporting a limited number of address bits).

DMA can be done to NORMAL memory as well.