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References: <20230106220959.3398792-1-song@kernel.org> <83941b74-7585-235b-ee54-3b127ca70d9e@csgroup.eu>
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From:   Song Liu <song@kernel.org>
Date:   Mon, 9 Jan 2023 10:24:30 -0800
Message-ID: <CAPhsuW6S8qJWFzSLpVf_4ZpyM0Cxty=-pS2_K=tgF52s95Zhag@mail.gmail.com>
Subject: Re: [PATCH/RFC] module: replace module_layout with module_memory
To:     Christophe Leroy <christophe.leroy@csgroup.eu>
Cc:     "linux-modules@vger.kernel.org" <linux-modules@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "songliubraving@fb.com" <songliubraving@fb.com>,
        Luis Chamberlain <mcgrof@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>
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On Mon, Jan 9, 2023 at 10:03 AM Christophe Leroy
<christophe.leroy@csgroup.eu> wrote:
>
>
>
> Le 06/01/2023 =C3=A0 23:09, Song Liu a =C3=A9crit :
> > module_layout manages different types of memory (text, data, rodata, et=
c.)
> > in one allocation, which is problematic for some reasons:
> >
> > 1. It is hard to enable CONFIG_STRICT_MODULE_RWX.
> > 2. It is hard to use huge pages in modules (and not break strict rwx).
> > 3. Many archs uses module_layout for arch-specific data, but it is not
> >     obvious how these data are used (are they RO, RX, or RW?)
> >
> > Improve the scenario by replacing 2 (or 3) module_layout per module wit=
h
> > up to 7 module_memory per module:
> >
> >          MOD_MEM_TYPE_TEXT,
> >          MOD_MEM_TYPE_DATA,
> >          MOD_MEM_TYPE_RODATA,
> >          MOD_MEM_TYPE_RO_AFTER_INIT,
> >          MOD_MEM_TYPE_INIT_TEXT,
> >          MOD_MEM_TYPE_INIT_DATA,
> >          MOD_MEM_TYPE_INIT_RODATA,
> >
> > and allocating them separately.
> >
> > Various archs use module_layout for different data. These data are put
> > into different module_memory based on their location in module_layout.
> > IOW, data that used to go with text is allocated with MOD_MEM_TYPE_TEXT=
;
> > data that used to go with data is allocated with MOD_MEM_TYPE_DATA, etc=
.
>
> I dislike how it looks with enums, things like
> mod->mod_mem[MOD_MEM_TYPE_INIT_TEXT] are odd and don't read nicely.
> Could we have something nicer like mod->mod_mem_init_text ?
> I know it will complicate your for_each_mod_mem_type() but it would look
> nicer.

Hmm.. I am not sure whether we want 7 module_memory here. But if we
agree that it looks better like that, I am ok with it.

>
> Also, can you explain how you switch from two trees to only one ?
> As far as I remember, the same question arised when I implemented
> CONFIG_ARCH_WANTS_MODULES_DATA_IN_VMALLOC, and the conclusion was that
> we had to keep two independant trees, so I'm a bit puzzled that you have
> now merged everything into a single tree.

AFAICT, we only need __module_address() to work? So one tree is enough.
Did I miss something?

Thanks,
Song