Re: [PATCH 1/1] arm/module: maximum utilization of module area.

[Ard Biesheuvel]

On 6 December 2016 at 08:29, Maninder Singh <maninder1.s@xxxxxxxxxxx> wrote:
> This patch defines new macro MODULE_START to ensure kernel text
> and module remains within 32 MB of address range.
>
> Tried this patch by inserting 20 MB size module on 4.1 kernel:-
>
> Earlier:-
> ==========
> sh# insmod size.ko
> ....
> insmod: ERROR: could not insert module size.ko: Cannot allocate memory
> sh#
>
> With this patch
> ===============
> sh# insmod size.ko
> ...
> sh# lsmod
> Module                  Size  Used by
> size                20972425  0
>
> Signed-off-by: Vaneet Narang <v.narang@xxxxxxxxxxx>
> Signed-off-by: Maninder Singh <maninder1.s@xxxxxxxxxxx>
> Reviewed-by: Ajeet Yadav <ajeet.y@xxxxxxxxxxx>
> ---
>  arch/arm/include/asm/memory.h | 4 ++--
>  arch/arm/kernel/module.c      | 9 ++++++++-
>  2 files changed, 10 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index 76cbd9c..1a0a6e5 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -37,7 +37,7 @@
>   * TASK_SIZE - the maximum size of a user space task.
>   * TASK_UNMAPPED_BASE - the lower boundary of the mmap VM area
>   */
> -#define TASK_SIZE              (UL(CONFIG_PAGE_OFFSET) - UL(SZ_16M))
> +#define TASK_SIZE              (UL(CONFIG_PAGE_OFFSET) - UL(SZ_32M))
>  #define TASK_UNMAPPED_BASE     ALIGN(TASK_SIZE / 3, SZ_16M)
>
>  /*
> @@ -50,7 +50,7 @@
>   * and PAGE_OFFSET - it must be within 32MB of the kernel text.
>   */
>  #ifndef CONFIG_THUMB2_KERNEL
> -#define MODULES_VADDR          (PAGE_OFFSET - SZ_16M)
> +#define MODULES_VADDR          (PAGE_OFFSET - SZ_32M)
>  #else
>  /* smaller range for Thumb-2 symbols relocation (2^24)*/
>  #define MODULES_VADDR          (PAGE_OFFSET - SZ_8M)
> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> index 4f14b5c..b8e1f9c 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -35,12 +35,19 @@
>   */
>  #undef MODULES_VADDR
>  #define MODULES_VADDR  (((unsigned long)_exiprom + ~PMD_MASK) & PMD_MASK)
> +#define MODULES_START MODULES_VADDR
> +#else
> +#ifndef CONFIG_THUMB2_KERNEL
> +#define MODULES_START  ALIGN((unsigned long)_etext - SZ_32M, PAGE_SIZE)

On a multi_v7_defconfig kernel, the text size is >8 MB, which means
you are only adding ~7 MB to the module area, while consuming 16 MB of
additional address space. Given that 20 MB modules are very uncommon,
I think it is better to enable CONFIG_ARM_MODULE_PLTS instead. That
way, there is no need to update these defaults for everyone.

> +#else
> +#define MODULES_START MODULES_VADDR
> +#endif
>  #endif
>
>  #ifdef CONFIG_MMU
>  void *module_alloc(unsigned long size)
>  {
> -       void *p = __vmalloc_node_range(size, 1, MODULES_VADDR, MODULES_END,
> +       void *p = __vmalloc_node_range(size, 1, MODULES_START, MODULES_END,
>                                 GFP_KERNEL, PAGE_KERNEL_EXEC, 0, NUMA_NO_NODE,
>                                 __builtin_return_address(0));
>         if (!IS_ENABLED(CONFIG_ARM_MODULE_PLTS) || p)
> --
> 1.9.1
>
>
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