U-Boot relocates itself to the top of memory and is supposed to avoid using any memory below that region. This allows the maximum amount of memory to be available for loading images.
The lmb subsystem automatically protects U-Boot's code and data from being overwritten. It relies on this region being a contiguous area of memory. This setup has worked well for at least 15 years and has been documented in the README for as long.
The EFI_LOADER subsystem currently uses memory outside the U-Boot region when starting up.
Some of the downstream problems this causes are:
1. It can overwrite images that have been loaded 2. Requires lmb reservations to avoid (1) even if EFI_LOADER is not being used 3. Uses regions which scripts expect to be available, e.g. the existing kernel_addr_r variables 4. Introduces confusion as to what memory U-Boot can use for itself
This series sets up a very small region of memory which EFI can used at start-up, thus avoiding touching memory outside the U-Boot region.
There are still a few tables which are not in the bloblist, but that will be resolved separately.
Other than tables, the amount of API-visible memory allocated by EFI before booting is actually very small: 3 allocations, of a total of about 250 bytes. However, there are some areas where EFI allocations are done unnecessarily. For example efi_disk_add_dev() uses page-allocation to allocate an efi_device_path, then immediately frees it again. In this case it would be better to use malloc(). Since each allocation consumes a page (4KB), 256KB has been chosen for the size here, enough for 64 allocations.
As soon as efi_init_obj_list() is called, we know that the EFI subsystem is to be used, so we can relax the restrictions and allow EFI to use any memory it likes. This is handled using a simple boolean flag in BSS, since it cannot happen before relocation.
Changes in v4: - Expand the commit message - Reword the commit message since this feature is needed - Use a different technique to keep the memory-usage in place - Drop changes to pool allocation - Reorder the patches - Rewrite the cover letter - Make it a debug message for now
Changes in v3: - Add new patch to drop the memset() from efi_alloc() - Drop patch to convert device_path allocation to use malloc()
Changes in v2: - Drop patch 'Show more information in efi index' - Drop patch 'Avoid pool allocation in efi_get_memory_map_alloc()' - Add the word 'warning', use log_warning() and show the end address
Simon Glass (5): efi: Drop the memset() from efi_alloc() efi: Show the location of the bounce buffer when debugging event: Add a generic way to reserve memory efi: Reserve some memory for initial use efi: Keep early allocations to the U-Boot region
common/board_f.c | 1 + common/event.c | 1 + include/asm-generic/global_data.h | 6 ++++ include/efi_loader.h | 24 +++++++++++++- include/event.h | 11 +++++++ lib/efi_loader/efi_bootbin.c | 9 ++++++ lib/efi_loader/efi_memory.c | 54 ++++++++++++++++++++++++------- lib/efi_loader/efi_setup.c | 5 +++ test/py/tests/test_event_dump.py | 1 + 9 files changed, 100 insertions(+), 12 deletions(-)