linux-kernel - Re: [PATCH/RFC] module: replace module_layout with module

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Date:   Mon, 9 Jan 2023 10:24:30 -0800
From:   Song Liu <song@...nel.org>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "songliubraving@...com" <songliubraving@...com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH/RFC] module: replace module_layout with module_memory

On Mon, Jan 9, 2023 at 10:03 AM Christophe Leroy
<christophe.leroy@...roup.eu> wrote:
>
>
>
> Le 06/01/2023 à 23:09, Song Liu a écrit :
> > module_layout manages different types of memory (text, data, rodata, etc.)
> > 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 with
> > 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