Hi Guenter,

Thanks for running the test!

On Fri, Jan 27, 2023 at 12:40 PM Guenter Roeck [off-list ref] wrote:

On Thu, Jan 26, 2023 at 03:36:06PM -0800, Song Liu wrote:

quoted

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>

---

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;

Fixed this in my local branch:

diff --git c/kernel/module/main.c w/kernel/module/main.c
index 32f63c6eaa61..da2bca75e4a8 100644
--- c/kernel/module/main.c
+++ w/kernel/module/main.c

@@ -935,8 +935,6 @@ struct module_attribute module_uevent =
 static ssize_t show_coresize(struct module_attribute *mattr,
                             struct module_kobject *mk, char *buffer)
 {
-       unsigned int size = 0;
-
        return sprintf(buffer, "%u\n",
                       mk->mod->mod_mem[MOD_MEM_TYPE_TEXT].size);
 }

Song