Re: [RFC v3 -next] cma: Enforce non-zero pageblock_order during cma_init_reserved_mem()

[Anshuman Khandual]

On 10/11/24 20:26, Ritesh Harjani (IBM) wrote:
> cma_init_reserved_mem() checks base and size alignment with
> CMA_MIN_ALIGNMENT_BYTES. However, some users might call this during
> early boot when pageblock_order is 0. That means if base and size does
> not have pageblock_order alignment, it can cause functional failures
> during cma activate area.
> 
> So let's enforce pageblock_order to be non-zero during
> cma_init_reserved_mem().
> 
> Acked-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
> ---
> v2 -> v3: Separated the series into 2 as discussed in v2.
> [v2]: https://lore.kernel.org/linuxppc-dev/cover.1728585512.git.ritesh.list@xxxxxxxxx/
> 
>  mm/cma.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> 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;
> --
> 2.46.0
> 
> 

LGTM, hopefully this comment regarding CMA_MIN_ALIGNMENT_BYTES alignment
requirement will also probably remind us, to drop this new check in case
CMA_MIN_ALIGNMENT_BYTES no longer depends on pageblock_order later.

Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>