[PATCH] lmb: prohibit allocations above ram_top even from same bank

[Patrice CHOTARD]

On 12/11/24 17:27, Sughosh Ganu wrote:
> On Wed, 11 Dec 2024 at 21:50, Patrice CHOTARD
> <patrice.chotard at foss.st.com> wrote:
>>
>>
>>
>> On 12/7/24 16:57, Tom Rini wrote:
>>> On Mon, 02 Dec 2024 12:36:24 +0530, Sughosh Ganu wrote:
>>>
>>>> There are platforms which set the value of ram_top based on certain
>>>> restrictions that the platform might have in accessing memory above
>>>> ram_top, even when the memory region is in the same DRAM bank. So,
>>>> even though the LMB allocator works as expected, when trying to
>>>> allocate memory above ram_top, prohibit this by marking all memory
>>>> above ram_top as reserved, even if the said memory region is from the
>>>> same bank.
>>>>
>>>> [...]
>>>
>>> Applied to u-boot/master, thanks!
>>>
>> Hello
>>
>> This patch is breaking the boot on STM32MP135F-DK.
>>
>> On this platform, we got an area above gd->ram_top,
>> this area, reserved for OPTEE, is tagged with LMB_NOMAP in boot_fdt_add_mem_rsv_regions().
>>
>> Since this commit 1a48b0be93d4 ("lmb: prohibit allocations above ram_top even from same bank"),
>> this area is no more tagged as LMB_NOMAP, because it's previously been
>> tagged with LMB_NOOVERWRITE in lmb_add_memory().
>>
>> By not being tagged LMB_NOMAP, the MMU configuration is impacted and leads to a panic.
>>
>> I suggest to revert this patch.
> 
> I don't think that this patch should be reverted. If the said platform
> has a reserved memory region above ram_top, I would suggest to either
> a) move the ram_top on this platform so that the op-tee region gets
> marked as no-map in the lmb memory map, or b) do not use the lmb

In my explanation above, i indicated that before this commit, 
this area was marked as LMB_NOMAP in the lmb memory map by boot_fdt_add_mem_rsv_regions().
this is exactly what you described in the possible solution "a)".

But now with this commit, as lmb_add_memory() is called in lmb_init() the area above ram_top is marked LMB_NOOVERWRITE.
Then later, boot_fdt_add_mem_rsv_regions() is executed, but the area above ram_top can't be marked as
LMB_NOMAP as previously because it's already marked LMB_NOOVERWRITE. 


> memory map to configure the MMU -- can the MMU configuration logic not
> read the DT to get which regions are to be marked as no-map?
> 
> As far as the lmb module is concerned, it is being told through this
> commit to not consider memory above ram_top for allocations, which is
> not an incorrect thing imo.

That's the case, we don't consider memory above ram_top for allocations,
we only marked it with LMB_NOMAP.

Thanks
Patrice

> 
> -sughosh
> 
>>
>> Patrice