[PATCH v2 1/6] efi: Allocate half of available memory by default

[Patrick Steinhardt <ps@pks.im>]

By default, GRUB will allocate a quarter of the pages it got available
in the EFI subsystem. On many current systems, this will amount to
roughly 800MB of RAM assuming an address space of 32 bits. This is
plenty for most use cases, but it doesn't suffice when using full disk
encryption with a key derival function based on Argon2.

Besides the usual iteration count known from PBKDF2, Argon2 introduces
two additional parameters "memory" and "parallelism". While the latter
doesn't really matter to us, the memory parameter is quite interesting.
If encrypting a partition with LUKS2 using Argon2 as KDF, then
cryptsetup will default to a memory parameter of 1GB. Meaning we need to
allocate a buffer of 1GB in size in order to be able to derive the key,
which definitely won't squeeze into the limit of 800MB.

To prepare for Argon2, let's thus increase the default and make half of
memory available, instead of a quarter only. This amounts to about
1600MB on above systems, which is sufficient for Argon2.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
---
 grub-core/kern/efi/mm.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/grub-core/kern/efi/mm.c b/grub-core/kern/efi/mm.c
index b02fab1b1..d1f9d046b 100644
--- a/grub-core/kern/efi/mm.c
+++ b/grub-core/kern/efi/mm.c
@@ -599,10 +599,10 @@ grub_efi_mm_init (void)
   filtered_memory_map_end = filter_memory_map (memory_map, filtered_memory_map,
 					       desc_size, memory_map_end);
 
-  /* By default, request a quarter of the available memory.  */
+  /* By default, request half of the available memory.  */
   total_pages = get_total_pages (filtered_memory_map, desc_size,
 				 filtered_memory_map_end);
-  required_pages = (total_pages >> 2);
+  required_pages = (total_pages / 2);
   if (required_pages < BYTES_TO_PAGES (MIN_HEAP_SIZE))
     required_pages = BYTES_TO_PAGES (MIN_HEAP_SIZE);
   else if (required_pages > BYTES_TO_PAGES (MAX_HEAP_SIZE))
-- 
2.25.1