linux-kernel - Re: [PATCH v3] module: replace module_layout with module

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Message-ID: <20230127204011.GA45594@roeck-us.net>
Date:   Fri, 27 Jan 2023 12:40:11 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Song Liu <song@...nel.org>
Cc:     linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...a.com, Luis Chamberlain <mcgrof@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3] module: replace module_layout with module_memory

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@...nel.org>
> Cc: Luis Chamberlain <mcgrof@...nel.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Guenter Roeck <linux@...ck-us.net>
> 
> ---

Build reference: v6.2-rc5-52-gc96fb00
Compiler version: powerpc64-linux-gcc (GCC) 11.3.0
Assembler version: GNU assembler (GNU Binutils) 2.39

Building powerpc:defconfig ... passed
Building powerpc:allmodconfig ... passed
Building powerpc:ppc32_allmodconfig ... failed
--------------
Error log:
kernel/module/main.c: In function 'show_coresize':
kernel/module/main.c:938:22: error: unused variable 'size' [-Werror=unused-variable]
  938 |         unsigned int size = 0;

That is the only failure reported by my test system.

Guenter