[patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap_atomic & friends

[Linus Torvalds]

On Sat, Sep 19, 2020 at 10:39 AM Matthew Wilcox <willy at infradead.org> wrote:
>
> My concern with that is people might use kmap() and then pass the address
> to a different task.  So we need to audit the current users of kmap()
> and convert any that do that into using vmap() instead.

Ahh. Yes, I guess they might do that. It sounds strange, but not
entirely crazy - I could imagine some "PIO thread" that does IO to a
page that has been set up by somebody else using kmap(). Or similar.

                Linus