linux-kernel - Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of kmap

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Date:   Sat, 19 Sep 2020 12:13:01 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Paul McKenney <paulmck@...nel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
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        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Will Deacon <will@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
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        "David S. Miller" <davem@...emloft.net>,
        linux-sparc <sparclinux@...r.kernel.org>
Subject: Re: [patch RFC 00/15] mm/highmem: Provide a preemptible variant of
 kmap_atomic & friends

On Sat, Sep 19, 2020 at 10:39 AM Matthew Wilcox <willy@...radead.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