EFI memory allocation

[Ilias Apalodimas]

Hi Simon

On Sun, 3 Dec 2023 at 19:44, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Heinrich, Ilias,
>
> I had a bit of a look at how memory is allocated in EFI.
>
> I see that efi_memory_init() is called quite early in U-Boot. It
> sometimes allocates memory for a bounce buffer, placing it somewhere
> in memory. How do we know that that memory is free and not being used
> by U-Boot?
>
> To answer my own question, it excludes U-Boot's malloc() region from
> the map, so that it cannot overwrite that.
>
> But then, what if we use lmb and start loading images into memory.
> Won't that conflict with EFI?

Yes, Heinrich tried to fix parts of this with commit 06d514d77c37 and
we have a 'todo' in the efi subsystem for a few years now [0]
Michal (+cc'ed) has also pinged me for similar issues in the past.

>
> I also see that efi_allocate_pages() is called to allocate memory in
> the EFI code. But this just grabs memory from 'anywhere'...it doesn't
> respect the U-Boot malloc region.
>
> It seems to me that most of the memory allocation in EFI should be
> done using malloc(). Of course the boot services need to
> efi_allocate_pages(), etc., but I am not sure that the internal tables
> should be skipping malloc()?
>
> What do you think?

I think that LMB, EFI and the whole memory reservations is a bit of a
mess. Tom and I discussed this a bit in the past but I'll start
working on it.
It needs fixing, but without looking at the code first, I can't
provide any useful feedback

[0] https://source.denx.de/u-boot/custodians/u-boot-efi/-/issues/2

Thanks
/Ilias
>
> Regards,
> Simon