Date:   Thu, 26 Jan 2023 15:58:25 -0800
From:   Luis Chamberlain <mcgrof@kernel.org>
To:     Song Liu <song@kernel.org>
Cc:     linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com, Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>,
        Guenter Roeck <linux@roeck-us.net>
Subject: Re: [PATCH v3] module: replace module_layout with module_memory
Message-ID: <Y9MToQW512fmyEYl@bombadil.infradead.org>
References: <20230126233606.1317794-1-song@kernel.org>
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Sender: Luis Chamberlain <mcgrof@infradead.org>
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On Thu, Jan 26, 2023 at 03:36:06PM -0800, 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_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. 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>

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>

I'll add this new version to modules-testing. If we get any other
Reviewed-by, I'll throw onto modules-next.

  Luis