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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Sun, 20 Sep 2020 22:49:03 +0200
Message-ID: <CAK8P3a37BRFj_qg61gP2oVrjJzBrZ58y1vggeTk_5n55Ou5U2Q@mail.gmail.com>
Subject: Re: [PATCH 1/9] kernel: add a PF_FORCE_COMPAT flag
To:     Andy Lutomirski <luto@kernel.org>
Cc:     Matthew Wilcox <willy@infradead.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Christoph Hellwig <hch@lst.de>,
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On Sun, Sep 20, 2020 at 9:28 PM Andy Lutomirski <luto@kernel.org> wrote:
> On Sun, Sep 20, 2020 at 12:23 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > On Sun, Sep 20, 2020 at 08:10:31PM +0100, Al Viro wrote:
> > > IMO it's much saner to mark those and refuse to touch them from io_uring...
> >
> > Simpler solution is to remove io_uring from the 32-bit syscall list.
> > If you're a 32-bit process, you don't get to use io_uring.  Would
> > any real users actually care about that?
>
> We could go one step farther and declare that we're done adding *any*
> new compat syscalls :)

Would you also stop adding system calls to native 32-bit systems then?

On memory constrained systems (less than 2GB a.t.m.), there is still a
strong demand for running 32-bit user space, but all of the recent Arm
cores (after Cortex-A55) dropped the ability to run 32-bit kernels, so
that compat mode may eventually become the primary way to run
Linux on cheap embedded systems.

I don't think there is any chance we can realistically take away io_uring
from the 32-bit ABI any more now.

      Arnd