linux-kernel - Re: [PATCH v5 bpf-next 1/5] module: introduce module_alloc

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Message-ID: <Yr+BV+HLZikpCU42@bombadil.infradead.org>
Date:   Fri, 1 Jul 2022 16:20:55 -0700
From:   Luis Chamberlain <mcgrof@...nel.org>
To:     Song Liu <song@...nel.org>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        x86@...r.kernel.org, dave.hansen@...ux.intel.com,
        rick.p.edgecombe@...el.com, kernel-team@...com,
        daniel@...earbox.net
Subject: Re: [PATCH v5 bpf-next 1/5] module: introduce module_alloc_huge

On Fri, Jun 24, 2022 at 02:57:08PM -0700, Song Liu wrote:
> Introduce module_alloc_huge, which allocates huge page backed memory in
> module memory space. The primary user of this memory is bpf_prog_pack
> (multiple BPF programs sharing a huge page).
> 
> Signed-off-by: Song Liu <song@...nel.org>

I see mm not Cc'd. I'd like review from them.

> ---
>  arch/x86/kernel/module.c     | 21 +++++++++++++++++++++
>  include/linux/moduleloader.h |  5 +++++
>  kernel/module/main.c         |  8 ++++++++
>  3 files changed, 34 insertions(+)
> 
> diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c
> index b98ffcf4d250..63f6a16c70dc 100644
> --- a/arch/x86/kernel/module.c
> +++ b/arch/x86/kernel/module.c
> @@ -86,6 +86,27 @@ void *module_alloc(unsigned long size)
>  	return p;
>  }
>  
> +void *module_alloc_huge(unsigned long size)
> +{
> +	gfp_t gfp_mask = GFP_KERNEL;
> +	void *p;
> +
> +	if (PAGE_ALIGN(size) > MODULES_LEN)
> +		return NULL;
> +
> +	p = __vmalloc_node_range(size, MODULE_ALIGN,
> +				 MODULES_VADDR + get_module_load_offset(),
> +				 MODULES_END, gfp_mask, PAGE_KERNEL,
> +				 VM_DEFER_KMEMLEAK | VM_ALLOW_HUGE_VMAP,
> +				 NUMA_NO_NODE, __builtin_return_address(0));
> +	if (p && (kasan_alloc_module_shadow(p, size, gfp_mask) < 0)) {
> +		vfree(p);
> +		return NULL;
> +	}
> +
> +	return p;
> +}

1) When things like kernel/bpf/core.c start using a module alloc it
   is time to consider genearlizing this.

2) How we free is important, and each arch does something funky for
   this. This is not addressed here.

And yes I welcome generalizing generic module_alloc() too as suggested
before. The concern on my part is the sloppiness this enables.

  Luis

> +
>  #ifdef CONFIG_X86_32
>  int apply_relocate(Elf32_Shdr *sechdrs,
>  		   const char *strtab,
> diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h
> index 9e09d11ffe5b..d34743a88938 100644
> --- a/include/linux/moduleloader.h
> +++ b/include/linux/moduleloader.h
> @@ -26,6 +26,11 @@ unsigned int arch_mod_section_prepend(struct module *mod, unsigned int section);
>     sections.  Returns NULL on failure. */
>  void *module_alloc(unsigned long size);
>  
> +/* Allocator used for allocating memory in module memory space. If size is
> + * greater than PMD_SIZE, allow using huge pages. Returns NULL on failure.
> + */
> +void *module_alloc_huge(unsigned long size);
> +
>  /* Free memory returned from module_alloc. */
>  void module_memfree(void *module_region);
>  
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index fed58d30725d..349b2a8bd20f 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -1613,6 +1613,14 @@ void * __weak module_alloc(unsigned long size)
>  			NUMA_NO_NODE, __builtin_return_address(0));
>  }
>  
> +void * __weak module_alloc_huge(unsigned long size)
> +{
> +	return __vmalloc_node_range(size, 1, VMALLOC_START, VMALLOC_END,
> +				    GFP_KERNEL, PAGE_KERNEL_EXEC,
> +				    VM_FLUSH_RESET_PERMS | VM_ALLOW_HUGE_VMAP,
> +				    NUMA_NO_NODE, __builtin_return_address(0));
> +}
> +
>  bool __weak module_init_section(const char *name)
>  {
>  	return strstarts(name, ".init");
> -- 
> 2.30.2
>