linux-kernel - Re: [PATCH v8] module: replace module_layout with module

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Date:   Thu, 2 Feb 2023 19:49:10 +0000
From:   Song Liu <songliubraving@...a.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
CC:     Song Liu <song@...nel.org>,
        "linux-modules@...r.kernel.org" <linux-modules@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "hch@....de" <hch@....de>, Kernel Team <kernel-team@...a.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v8] module: replace module_layout with module_memory



> On Feb 1, 2023, at 11:23 PM, Christophe Leroy <christophe.leroy@...roup.eu> wrote:
> 
> 
> 
> Le 01/02/2023 à 23:32, 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_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@...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>
>> Cc: Christophe Leroy <christophe.leroy@...roup.eu>
>> 
> 
>   CALL    scripts/checksyscalls.sh
>   CC      kernel/module/main.o
> kernel/module/main.c: In function 'mod_mem_use_vmalloc':
> kernel/module/main.c:1175:16: error: implicit declaration of function 
> 'mod_mem_is_core_data'; did you mean 'mod_mem_type_is_core_data'? 
> [-Werror=implicit-function-declaration]
>  1175 |         return mod_mem_is_core_data(type);
>       |                ^~~~~~~~~~~~~~~~~~~~
>       |                mod_mem_type_is_core_data
> cc1: some warnings being treated as errors
> make[3]: *** [scripts/Makefile.build:252: kernel/module/main.o] Error 1
> make[2]: *** [scripts/Makefile.build:504: kernel/module] Error 2
> make[1]: *** [scripts/Makefile.build:504: kernel] Error 2
> make: *** [Makefile:2024: .] Error 2

Oops..  

Let me get this through build tests by kernel test bot.

Thanks,
Song