Re: [PATCH v4] module: replace module_layout with module_memory

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 <redacted>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Christophe Leroy <redacted>

---

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.