Date:   Wed, 8 Feb 2023 08:06:58 -0800
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Thomas Gleixner <tglx@linutronix.de>
Cc:     Song Liu <song@kernel.org>, linux-modules@vger.kernel.org,
        linux-kernel@vger.kernel.org, hch@lst.de, kernel-team@meta.com,
        Peter Zijlstra <peterz@infradead.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [PATCH v10] module: replace module_layout with module_memory
Message-ID: <Y+PIohsycXjJpdr5@bombadil.infradead.org>
References: <20230207002802.2514802-1-song@kernel.org>
 <87357gv9ha.ffs@tglx>
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On Wed, Feb 08, 2023 at 09:37:21AM +0100, Thomas Gleixner wrote:
> On Mon, Feb 06 2023 at 16:28, Song Liu wrote:
> > 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_TEXT,
> >         MOD_DATA,
> >         MOD_RODATA,
> >         MOD_RO_AFTER_INIT,
> >         MOD_INIT_TEXT,
> >         MOD_INIT_DATA,
> >         MOD_INIT_RODATA,
> >
> > and allocating them separately. This adds slightly more entries to
> > mod_tree (from up to 3 entries per module, to up to 7 entries per
> > module). However, this at most adds a small constant overhead to
> > __module_address(), which is expected to be fast.
> >
> > 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.
> >
> > module_memory simplifies quite some of the module code. For example,
> > ARCH_WANTS_MODULES_DATA_IN_VMALLOC is a lot cleaner, as it just uses a
> > different allocator for the data. kernel/module/strict_rwx.c is also
> > much cleaner with module_memory.
> >
> > Signed-off-by: Song Liu <song@kernel.org>
> > Cc: Luis Chamberlain <mcgrof@kernel.org>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Guenter Roeck <linux@roeck-us.net>
> > Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> 
> With the comment update folded in:
> 
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

Thanks! I've merged this onto modules-next for winder testing.
It is too late for v6.2 as we're on rc7 but this just means we'll
get testing on linux-next for a good while for v6.3.

If other folks do complete review please send your Reviewed-by
annotation so I can ammend the commit log as we go.

  Luis