[PATCH v4 0/5] Adjust initial EFI memory-allocation to be in the U-Boot region

[Simon Glass]

Hi Ilias,

On Mon, 14 Oct 2024 at 22:28, Ilias Apalodimas
<ilias.apalodimas at linaro.org> wrote:
>
> Hi Simon,
>
> On Sat, 12 Oct 2024 at 00:23, Simon Glass <sjg at chromium.org> wrote:
> >
> > 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
>
> So can the load command

Can you point to where? If lmb is enabled, it should be using that, so
not overwrite anything.

>
> > 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.
>
> EFI *is* U-Boot memory region. It lies outside the U-Boot binary,
> because some services are instantiated on boot. It also *is* U-Boot
> executable code. We should start treating it as such

This seems like semantics to me. What do you think of this patch?

Regards,
Simon


>
> Thanks
> /Ilias
> >
> > 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(-)
> >
> > --
> > 2.34.1
> >