[RFC 1/2] cma: Fix CMA_MIN_ALIGNMENT_BYTES during early_init

[David Hildenbrand]

On 08.10.24 15:27, Ritesh Harjani (IBM) wrote:
> During early init CMA_MIN_ALIGNMENT_BYTES can be PAGE_SIZE,
> since pageblock_order is still zero and it gets initialized
> later during paging_init() e.g.
> paging_init() -> free_area_init() -> set_pageblock_order().
> 
> One such use case is -
> early_setup() -> early_init_devtree() -> fadump_reserve_mem()
> 
> This causes CMA memory alignment check to be bypassed in
> cma_init_reserved_mem(). Then later cma_activate_area() can hit
> a VM_BUG_ON_PAGE(pfn & ((1 << order) - 1)) if the reserved memory
> area was not pageblock_order aligned.
> 
> Instead of fixing it locally for fadump case on PowerPC, I believe
> this should be fixed for CMA_MIN_ALIGNMENT_BYTES.

I think we should add a way to catch the usage of 
CMA_MIN_ALIGNMENT_BYTES before it actually has meaning (before 
pageblock_order was set) and fix the PowerPC usage by reshuffling the 
code accordingly.

-- 
Cheers,

David / dhildenb