linux-kernel - Re: sparc32: Init process fails to load with generic kmap atomic

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Message-ID: <CAK8P3a1KioFh+BFpXycWhVtvaEu5qvaTLuqtw7NbYfKzCOiFsg@mail.gmail.com>
Date:   Tue, 22 Dec 2020 21:13:59 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Andreas Larsson <andreas@...sler.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        sparclinux <sparclinux@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        "David S. Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: sparc32: Init process fails to load with generic kmap atomic

On Tue, Dec 22, 2020 at 7:01 PM Andreas Larsson <andreas@...sler.com> wrote:
>
> Unfortunately I did not see this problem before I encountered it in
> master. Commit 3293efa9780712ad8504689e0c296d2bd33827d5
>
...
>
> I will have to continue to dig deeper into this in January. If anyone
> has any ideas how this could stem from this kmap patch, I am all ears.

I don't immediately see it, but an easy thing to try would be to
disable CONFIG_HIGHMEM. I don't know what the limits are
on sparc, but you can often change the virtual address layout
to reserve enough space for mapping all of the physical memory,
as e.g. CONFIG_VMSPLIT_2G does on x86 or arm.

There is also some discussion about eventually removing highmem
support from the kernel entirely.

       Arnd