Re: [PATCH/RFC] module: replace module_layout with module_memory

From: Song Liu <song@kernel.org>
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>
Subject: Re: [PATCH/RFC] module: replace module_layout with module_memory
Date: Mon, 9 Jan 2023 12:51:59 -0800	[thread overview]
Message-ID: <CAPhsuW7+BG9wYaoD6EYH-jnWqX30JdgNr5_733sO-++SzR5v3w@mail.gmail.com> (raw)
In-Reply-To: <CAPhsuW6S8qJWFzSLpVf_4ZpyM0Cxty=-pS2_K=tgF52s95Zhag@mail.gmail.com>

On Mon, Jan 9, 2023 at 10:24 AM Song Liu <song@kernel.org> wrote:
>
> On Mon, Jan 9, 2023 at 10:03 AM Christophe Leroy
> <christophe.leroy@csgroup.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?

Do you mean one tree will cause addr_[min|max] to be inaccurate?

Thanks,
Song