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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Sat, 19 Sep 2020 12:13:01 -0700
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Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of
 kmap_atomic & friends
To:     Matthew Wilcox <willy@infradead.org>
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On Sat, Sep 19, 2020 at 10:39 AM Matthew Wilcox <willy@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