linux-kernel - Re: [PATCH] riscv: export flush_icache

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Message-ID: <CAOesGMg_VySkckuTfeMWkfcQ6fUBokAQbCGXP9emz9WvtX4fKQ@mail.gmail.com>
Date:   Fri, 20 Dec 2019 14:29:20 -0800
From:   Olof Johansson <olof@...om.net>
To:     Paul Walmsley <paul.walmsley@...ive.com>
Cc:     Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        linux-riscv@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH] riscv: export flush_icache_all to modules

On Fri, Dec 20, 2019 at 3:05 AM Paul Walmsley <paul.walmsley@...ive.com> wrote:
>
> On Mon, 16 Dec 2019, Olof Johansson wrote:
>
> > This is needed by LKDTM (crash dump test module), it calls
> > flush_icache_range(), which on RISC-V turns into flush_icache_all(). On
> > other architectures, the actual implementation is exported, so follow
> > that precedence and export it here too.
> >
> > Fixes build of CONFIG_LKDTM that fails with:
> > ERROR: "flush_icache_all" [drivers/misc/lkdtm/lkdtm.ko] undefined!
>
> In the past we've resisted doing this; see
>
> https://lore.kernel.org/linux-riscv/20190611134945.GA28532@lst.de/
>
> under the principle that we don't want modules to be able to flush the I$
> directly via this interface.  But maybe, like moving the L2 related code
> out of arch/riscv, we should just do it.

So you are aware that all other architectures that don't have coherent
icache already exports this, right?

Being more puritan on RISC-V buys nothing w.r.t. keeping modules from
doing anything, you'll just end up having to mark a bunch of them
broken on your architecture. :(


-Olof