linux-kernel - Re: [RFC v2 1/4] cma: Enforce non-zero pageblock_order during cma_init_reserved

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Message-ID: <e894f6f2-d93f-4787-af40-7f021a40b156@redhat.com>
Date: Fri, 11 Oct 2024 12:12:48 +0200
From: David Hildenbrand <david@...hat.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
 linuxppc-dev@...ts.ozlabs.org
Cc: linux-mm@...ck.org, Sourabh Jain <sourabhjain@...ux.ibm.com>,
 Hari Bathini <hbathini@...ux.ibm.com>, Zi Yan <ziy@...dia.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
 Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
 Michael Ellerman <mpe@...erman.id.au>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>,
 "Aneesh Kumar K . V" <aneesh.kumar@...nel.org>,
 Donet Tom <donettom@...ux.vnet.ibm.com>, LKML
 <linux-kernel@...r.kernel.org>, Sachin P Bappalige <sachinpb@...ux.ibm.com>
Subject: Re: [RFC v2 1/4] cma: Enforce non-zero pageblock_order during
 cma_init_reserved_mem()

On 11.10.24 09:23, 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().
> 
> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
> ---
>   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;

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb