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

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Message-ID: <CAPhsuW4nPo_OFwspn18N-pKpPjc6vOYBJp8hE7O5mYEweKUySg@mail.gmail.com>
Date:   Fri, 27 Jan 2023 13:31:51 -0800
From:   Song Liu <song@...nel.org>
To:     Guenter Roeck <linux@...ck-us.net>
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

Hi Guenter,

Thanks for running the test!

On Fri, Jan 27, 2023 at 12:40 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> 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;

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