linux-kernel - Re: [PATCH 31/31] module: move the set_fs hack for flush_icache

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Message-ID: <CAMuHMdW1S91i3x0unNcJnypHse7ifynGb4dZcVhJaemR3GH1Pg@mail.gmail.com>
Date:   Mon, 11 May 2020 17:24:30 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Roman Zippel <zippel@...ux-m68k.org>,
        Jessica Yu <jeyu@...nel.org>, Michal Simek <monstr@...str.eu>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        alpha <linux-alpha@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-c6x-dev@...ux-c6x.org,
        "open list:QUALCOMM HEXAGON..." <linux-hexagon@...r.kernel.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        linux-m68k <linux-m68k@...ts.linux-m68k.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Openrisc <openrisc@...ts.librecores.org>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        linux-riscv@...ts.infradead.org,
        Linux-sh list <linux-sh@...r.kernel.org>,
        sparclinux <sparclinux@...r.kernel.org>,
        Linux-Arch <linux-arch@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-um <linux-um@...ts.infradead.org>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>,
        Linux FS Devel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 31/31] module: move the set_fs hack for flush_icache_range
 to m68k

Hi Christoph,

On Mon, May 11, 2020 at 5:11 PM Christoph Hellwig <hch@....de> wrote:
> On Mon, May 11, 2020 at 09:40:39AM +0200, Geert Uytterhoeven wrote:
> > On Sun, May 10, 2020 at 9:57 AM Christoph Hellwig <hch@....de> wrote:
> > >
> > > flush_icache_range generally operates on kernel addresses, but for some
> > > reason m68k needed a set_fs override.  Move that into the m68k code
> > > insted of keeping it in the module loader.
> > >
> > > Signed-off-by: Christoph Hellwig <hch@....de>
> >
> > Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> > Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>
> Btw, do you know what part of flush_icache_range relied on set_fs?
> Do any of the m68k maintainers have an idea how to handle that in
> a nicer way when we can split the implementations?

arch/m68k/mm/cache.c:virt_to_phys_slow()

All instructions that look up addresses in the page tables look at the
source/destination function codes (SFC/DFC) to know if they have to use
the supervisor or user page tables.
So the actual implementation is the same: set_fs() merely configures
SFC/DFC, to select the address space to use.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds