Re: [PATCH 2/2] mm/page_alloc.c: add config option to sanitize freed pages

[David Rientjes <rientjes@google.com>]

On Fri, 24 Apr 2015, Anisse Astier wrote:

> diff --git a/mm/Kconfig b/mm/Kconfig
> index 390214d..cb2df5f 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -635,3 +635,15 @@ config MAX_STACK_SIZE_MB
>  	  changed to a smaller value in which case that is used.
>  
>  	  A sane initial value is 80 MB.
> +
> +config SANITIZE_FREED_PAGES
> +	bool "Sanitize memory pages after free"
> +	default n
> +	help
> +	  This option is used to make sure all pages freed are zeroed. This is
> +	  quite low-level and doesn't handle your slab buffers.
> +	  It has various applications, from preventing some info leaks to
> +	  helping kernel same-page merging in virtualised environments.
> +	  Depending on your workload, it will reduce performance of about 3%.
> +
> +	  If unsure, say N.

Objection to allowing this without first enabling some other DEBUG config 
option, it should never be a standalone option, but also to pretending to 
have any insight into what the performance degredation of it will be.  On 
my systems, this would be _massive_.

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