linux-kernel - Re: [PATCH 1/5] alloc_tag: load module tags into separate continuous memory

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Message-ID: <ZsRCAy5cCp0Ig3I/@kernel.org>
Date: Tue, 20 Aug 2024 10:13:07 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, kent.overstreet@...ux.dev, corbet@....net,
	arnd@...db.de, mcgrof@...nel.org, paulmck@...nel.org,
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Subject: Re: [PATCH 1/5] alloc_tag: load module tags into separate continuous
 memory

On Mon, Aug 19, 2024 at 08:15:07AM -0700, Suren Baghdasaryan wrote:
> When a module gets unloaded there is a possibility that some of the
> allocations it made are still used and therefore the allocation tags
> corresponding to these allocations are still referenced. As such, the
> memory for these tags can't be freed. This is currently handled as an
> abnormal situation and module's data section is not being unloaded.
> To handle this situation without keeping module's data in memory,
> allow codetags with longer lifespan than the module to be loaded into
> their own separate memory. The in-use memory areas and gaps after
> module unloading in this separate memory are tracked using maple trees.
> Allocation tags arrange their separate memory so that it is virtually
> contiguous and that will allow simple allocation tag indexing later on
> in this patchset. The size of this virtually contiguous memory is set
> to store up to 100000 allocation tags and max_module_alloc_tags kernel
> parameter is introduced to change this size.
> 
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> ---
>  .../admin-guide/kernel-parameters.txt         |   4 +
>  include/asm-generic/codetag.lds.h             |  19 ++
>  include/linux/alloc_tag.h                     |  13 +-
>  include/linux/codetag.h                       |  35 ++-
>  kernel/module/main.c                          |  67 +++--
>  lib/alloc_tag.c                               | 245 ++++++++++++++++--
>  lib/codetag.c                                 | 101 +++++++-
>  scripts/module.lds.S                          |   5 +-
>  8 files changed, 429 insertions(+), 60 deletions(-)
 
...

> diff --git a/include/linux/codetag.h b/include/linux/codetag.h
> index c2a579ccd455..c4a3dd60205e 100644
> --- a/include/linux/codetag.h
> +++ b/include/linux/codetag.h
> @@ -35,8 +35,13 @@ struct codetag_type_desc {
>  	size_t tag_size;
>  	void (*module_load)(struct codetag_type *cttype,
>  			    struct codetag_module *cmod);
> -	bool (*module_unload)(struct codetag_type *cttype,
> +	void (*module_unload)(struct codetag_type *cttype,
>  			      struct codetag_module *cmod);
> +	void (*module_replaced)(struct module *mod, struct module *new_mod);
> +	bool (*needs_section_mem)(struct module *mod, unsigned long size);
> +	void *(*alloc_section_mem)(struct module *mod, unsigned long size,
> +				   unsigned int prepend, unsigned long align);
> +	void (*free_section_mem)(struct module *mod, bool unused);
>  };
>  
>  struct codetag_iterator {
> @@ -71,11 +76,31 @@ struct codetag_type *
>  codetag_register_type(const struct codetag_type_desc *desc);
>  
>  #if defined(CONFIG_CODE_TAGGING) && defined(CONFIG_MODULES)
> +
> +bool codetag_needs_module_section(struct module *mod, const char *name,
> +				  unsigned long size);
> +void *codetag_alloc_module_section(struct module *mod, const char *name,
> +				   unsigned long size, unsigned int prepend,
> +				   unsigned long align);
> +void codetag_free_module_sections(struct module *mod);
> +void codetag_module_replaced(struct module *mod, struct module *new_mod);
>  void codetag_load_module(struct module *mod);
> -bool codetag_unload_module(struct module *mod);
> -#else
> +void codetag_unload_module(struct module *mod);
> +
> +#else /* defined(CONFIG_CODE_TAGGING) && defined(CONFIG_MODULES) */
> +
> +static inline bool
> +codetag_needs_module_section(struct module *mod, const char *name,
> +			     unsigned long size) { return false; }
> +static inline void *
> +codetag_alloc_module_section(struct module *mod, const char *name,
> +			     unsigned long size, unsigned int prepend,
> +			     unsigned long align) { return NULL; }
> +static inline void codetag_free_module_sections(struct module *mod) {}
> +static inline void codetag_module_replaced(struct module *mod, struct module *new_mod) {}
>  static inline void codetag_load_module(struct module *mod) {}
> -static inline bool codetag_unload_module(struct module *mod) { return true; }
> -#endif
> +static inline void codetag_unload_module(struct module *mod) {}
> +
> +#endif /* defined(CONFIG_CODE_TAGGING) && defined(CONFIG_MODULES) */

Maybe I'm missing something, but can't alloc_tag::module_unload() just copy
the tags that cannot be freed somewhere outside of module sections and then
free the module?

The heavy lifting would be localized to alloc_tags rather than spread all
over.

-- 
Sincerely yours,
Mike.