David Hildenbrand <david@xxxxxxxxxx> writes:
> 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)
Maybe by enforcing that the pageblock_order should not be zero where we
do the alignment check then?
i.e. in cma_init_reserved_mem()
diff --git a/mm/cma.c b/mm/cma.c
index 3e9724716bad..36d753e7a0bf 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -182,6 +182,15 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
if (!size || !memblock_is_region_reserved(base, size))
return -EINVAL;
+ /*
+ * CMA uses CMA_MIN_ALIGNMENT_BYTES as alignment requirement which
+ * needs pageblock_order to be initialized. Let's enforce it.
+ */
+ if (!pageblock_order) {
+ pr_err("pageblock_order not yet initialized. Called during early boot?\n");
+ return -EINVAL;
+ }
+
/* ensure minimal alignment required by mm core */
if (!IS_ALIGNED(base | size, CMA_MIN_ALIGNMENT_BYTES))
return -EINVAL;
> and fix the PowerPC usage by reshuffling the
> code accordingly.
Ok. I will submit a v2 with the above patch incldued.
Thanks for the review!
-ritesh
