Re: [Xen-devel] [PATCH v2] mm: option to _always_ scrub freed domheap pages

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 07.05.19 at 13:34, <elnikety@xxxxxxxxxx> wrote:
> --- a/xen/common/page_alloc.c
> +++ b/xen/common/page_alloc.c
> @@ -214,6 +214,10 @@ custom_param("bootscrub", parse_bootscrub_param);
>  static unsigned long __initdata opt_bootscrub_chunk = MB(128);
>  size_param("bootscrub_chunk", opt_bootscrub_chunk);
>  
> + /* scrub-domheap -> Domheap pages are scrubbed when freed */
> +static bool __read_mostly opt_scrub_domheap;
> +boolean_param("scrub-domheap", opt_scrub_domheap);

Upon 2nd thought this, btw, would seem to be an excellent candidate
for becoming a runtime parameter.

> @@ -2378,9 +2382,10 @@ void free_domheap_pages(struct page_info *pg, unsigned 
> int order)
>              /*
>               * Normally we expect a domain to clear pages before freeing 
> them,
>               * if it cares about the secrecy of their contents. However, 
> after
> -             * a domain has died we assume responsibility for erasure.
> +             * a domain has died we assume responsibility for erasure. We do
> +             * scrub regardless if option scrub_domheap is set.
>               */
> -            scrub = d->is_dying || scrub_debug;
> +            scrub = d->is_dying || scrub_debug || opt_scrub_domheap;

Did you consider setting opt_scrub_domheap when scrub_debug is
set? This would shorten the (runtime) calculation here by a tiny bit,
at the price of doing one more thing once while booting.

Jan



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