Am 2021-10-31 18:36, schrieb Mark Kettenis:
Date: Sun, 31 Oct 2021 16:19:56 +0100
From: Michael Walle <mich...@walle.cc>
..
>> > Unless CONFIG_EFI_LOADER is defined. Then it relocates the spin table
>> > to memory allocated using efi_allocate_pages(). But that function
>> > only looks at the EFI memory map to figure out what memory is
>> > available. So I suspect that it might hand out the same memory as
>> > lmb_alloc(). It all looks a bit broken to me...
>>
>> Yes, that is actually my code ;) The kontron_sl28 is the only
>> board which uses spin tables as far as I know. It doesn't support
>> PSCI; at least if you don't load a bl31 TF-A. Therefore, for SMP
>> it uses spin tables. The relocation code work arounds a problem
>> with the reserved EFI code, see [1].
>>
>> And yes, it actually is broken. But so might be every code which
>> is using the efi_allocate_pages(), no? LMB isn't global, but is
>> just initialized at different places. Like before a linux kernel
>> is booted or when you load a file (?). And everytime the whole
>> memory is added, and then different regions are carved out (see
>> above).
>
> Right. So it mostly works because U-Boot either ends up using a code
> path where it uses LMB or a path where it ends up using the EFI memory
> map, but never both. Except if it hits your layerscape code.
>
> I think the right way to solve this is to allocate the memory for the
> spin table through some other means and use efi_add_memory_map() to
> reserve that memory like what is done in board/raspberrypi/rpi/rpi.c.
Mh. I don't think this will work, just because lmb is quite stupid
and has just the three steps to carve out memory:
(1) arch_lmb_reserve()
(2) board_lmb_reserve()
(3) boot_fdt_add_mem_rsv_regions()
(1) will carve out u-boot code and data (2) is usually not used and
(3) doesn't really work IMHO, because the reserved regions are added
much later in the bootm flow.
So what would "other means" be? I could allocate the memory somehow,
but how can I communicate that to lmb, so it would be excluded there.
It could be a simple:
memalign(PAGE_SIZE, PAGE_SIZE);
This would allocate memory from the heap which should be excluded from
what lmb hands out.
Thanks, that was easy ;) Turns out the heap is between the stack and the
uboot code which is reserved by lmb (arch_lmb_reserve()).
-michael
