Date:   Tue, 31 Jan 2023 12:36:42 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Song Liu <song@kernel.org>
Cc:     linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org,
        hch@lst.de, kernel-team@meta.com,
        Luis Chamberlain <mcgrof@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Guenter Roeck <linux@roeck-us.net>,
        Christophe Leroy <christophe.leroy@csgroup.eu>
Subject: Re: [PATCH v4] module: replace module_layout with module_memory
Message-ID: <Y9j9Svys7eb9E2Mh@hirez.programming.kicks-ass.net>
References: <20230130182109.3571524-1-song@kernel.org>
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On Mon, Jan 30, 2023 at 10:21:09AM -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>
> Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
> 
> ---
> 
> This is the preparation work for the type aware module_alloc() discussed
> in [1]. While this work is not covered much in the discussion, it is a
> critical step of the effort.
> 
> As this part grows pretty big (~1000 lines, + and -), I would like get
> some feedback on it, so that I know it is on the right track.
> 
> Please share your comments. Thanks!

Aside from the things already reported I like where this is going.