Re: [PATCH v2 1/5] of: reserved_mem: skip init for regions whose early reservation failed

[Marek Szyprowski]

On 31.08.2026 15:04, Wandun wrote:
> On 8/26/26 21:14, Marek Szyprowski wrote:
>> On 18.08.2026 11:24, Wandun Chen wrote:
>>> From: Wandun Chen <chenwandun@xxxxxxxxxxx>
>>>
>>> __reserved_mem_reserve_reg() discards the error from
>>> early_init_dt_reserve_memory() and returns 0 unconditionally, so the
>>> caller counts the node in total_reserved_mem_cnt and the late scan
>>> initializes it without checking whether the early reservation actually
>>> succeeded. A region whose reservation failed is then handed to a
>>> device assuming the memory is protected.
>>>
>>> Propagate the error so failed reservations are no longer counted, and
>>> record the failed nodes so fdt_scan_reserved_mem_late() can skip them.
>>>
>>> Recording the failed nodes explicitly is necessary because
>>> fdt_scan_reserved_mem_late() rescans the DT independently. It cannot
>>> tell from memblock whether early reservation succeeded.
>>>
>>> The failed-node array is bounded by MAX_RESERVED_REGIONS, the number
>>> of static regions is not bounded by it, so on overflow the extra nodes
>>> fall back to being initialized, which is the current behavior.
>> I'm not very keen on such partial solution. Indeed we have no place to
>>
>> store the result of the early init call, but we can check if the given
>>
>> region has been earlier marked in memblock as reserved or no-map in
>>
>> fdt_scan_reserved_mem_late(). If those attributes don't match the
>>
>> region can be simply skipped then.
> Considering the later patches that reject reservations for overlapping
> nodes, checking the memblock state in fdt_scan_reserved_mem_late() may
> produce false positives.
>
> For example, if region A is reserved first and region B is a subset of
> A, reserving B will fail because it overlaps with A (in patch 02/03).
> However, during fdt_scan_reserved_mem_late(), B will still appear to
> be reserved because its range is already covered by A. As a result,
> B would be initialized even though its own reservation failed, which
> is contrary to the intended behavior.
Imho the overlapping reserved regions are some kind of configuration 
mismatch and it is enough to detect them. fdt_scan_reserved_mem_late()
can first store all regions to dynamic reserved_mem array, then check
for overlaps, and only then initialize those, which don't overlap and
have proper memblock attributes?

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland