On Fri, Mar 13, 2020 at 12:55:08PM +0000, Leif Lindholm wrote: > My idea was something along the lines of (pseudocode - coding style, > macro use and naming may or may not be suitable): > > target_heap_pages = MIN_HEAP_PAGES; > #ifdef GRUB_LUKS2_ARGON2_ENABLED > target_heap_pages += GRUB_LUKS2_ARGON2_PAGES; > #endif > > and then > > if (target_heap_pages > (total_pages >> 2) > target_heap_pages = total_pages >> 2; > > and then possibly > > if (target_heap_pages > MAX_HEAP_PAGES) > target_heap_pages = MAX_HEAP_PAGES;
What do you think about the following algorithm:
/* Aim to satisfy requirements posed by both GRUB and other modules. */
target_pages = MIN_HEAP_PAGES;
#ifdef GRUB_LUKS2_ARGON2_ENABLED
target_pages += GRUB_LUKS2_ARGON2_PAGES;
#endif
total_pages = get_total_pages (filtered_memory_map, desc_size,
filtered_memory_map_end);
/* By default, request a quarter of the available memory. */
required_pages = (total_pages >> 2);
/* But try to satisfy requirements set forth by modules. */
required_pages = grub_max (required_pages, target_pages);
/* And clamp to MIN_HEAP_PAGES <= required_pages <= MAX_HEAP_PAGES. */
required_pages = grub_max (required_pages, MIN_HEAP_PAGES);
required_pages = grub_min (required_pages, MAX_HEAP_PAGES);
In the general case where GRUB_LUKS2_ARGON2_ENABLED is not set, it will
behave exactly the same as before: we request a quarter of available
pages and clamp to MIN_HEAP_PAGES <= required_pages <= MAX_HEAP_PAGES.
If GRUB_LUKS2_ARGON2_ENABLED is set, it will also behave that way,
except for the case where `required_pages < target_pages`, where we just
set `required_pages = target_pages`. As we're still doing the clamping,
we will end up with at most MAX_HEAP_PAGES (1.6GB), which should be
sufficient.
I think this is the least invasive way this can be implemented with
minimal risk: in the general case it is exactly the same as before.
Patrick
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