linux-kernel - Re: [PATCH 1/6] syscalls: use uaccess_kernel in addr_limit_user

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Message-ID: <CAFEAcA8=O6TbxYwmRwZJbcqFKi364=ueV_TsTu_84M5WFVtD8g@mail.gmail.com>
Date:   Mon, 20 Jul 2020 16:28:35 +0100
From:   Peter Maydell <peter.maydell@...aro.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        lkml - Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vladimir Murzin <vladimir.murzin@....com>,
        arm-mail-list <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/6] syscalls: use uaccess_kernel in addr_limit_user_check

On Mon, 20 Jul 2020 at 15:55, Guenter Roeck <linux@...ck-us.net> wrote:
> Ah, sorry, you can't use the upstream version of qemu to test mps2-an385
> Linux images. You'll have to use a version from https://github.com/groeck/qemu.
> I'd recommend to use the v5.0.0-local branch.
>
> I had to make some changes to qemu to be able to boot mps2-an385.
> I tried to submit those changes into upstream qemu, but that was
> rejected because, as I was told, the qemu implementation
> would no longer reflect the real hardware with those changes in
> place.

Yes; the rationale is that if you wanted to boot a kernel
on an actual MPS2 board you'd need a bit of guest code to
start it up (and to bundle the initrd/dtb in with it), so
since you need to write that code anyway you could use it for
booting the kernel in QEMU too.

I appreciate that this is awkward for kernel developers (and
perhaps for some other users too), but QEMU's handling of
-kernel and built-in-bootloader code is already a morass of
special cases and do-what-I-mean behaviour that I'm not
enthusiastic about further complicating :-)

(https://lists.gnu.org/archive/html/qemu-arm/2018-06/msg00393.html
has the archive of our original discussion on the point, for
other readers of this post interested in further context and
discussion.)

thanks
-- PMM