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From: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
To: David Hildenbrand <david@redhat.com>,
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	Ryan Roberts <ryan.roberts@arm.com>,
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Subject: Re: [PATCH v1 01/11] arm/pgtable: define PFN_PTE_SHIFT on arm and
 arm64
In-Reply-To: <3a970289-a72f-418e-b43c-89f67f0d5283@redhat.com>
References: <20240122194200.381241-1-david@redhat.com>
 <20240122194200.381241-2-david@redhat.com>
 <fdaeb9a5-d890-499a-92c8-d171df43ad01@arm.com>
 <46080ac1-7789-499b-b7f3-0231d7bd6de7@redhat.com>
 <6703b648-10ab-4fea-b7f1-75421319465b@arm.com>
 <ae3d826f-758f-4738-b72a-e99f098bb2b3@csgroup.eu>
 <3a970289-a72f-418e-b43c-89f67f0d5283@redhat.com>
Date: Wed, 24 Jan 2024 11:16:23 +0530
Message-ID: <87zfwvp9lc.fsf@kernel.org>
Precedence: bulk
MIME-Version: 1.0
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David Hildenbrand <david@redhat.com> writes:

>>>
>>>> If high bits are used for
>>>> something else, then we might produce a garbage PTE on overflow, but that
>>>> shouldn't really matter I concluded for folio_pte_batch() purposes, we'd not
>>>> detect "belongs to this folio batch" either way.
>>>
>>> Exactly.
>>>
>>>>
>>>> Maybe it's likely cleaner to also have a custom pte_next_pfn() on ppc, I just
>>>> hope that we don't lose any other arbitrary PTE bits by doing the pte_pgprot().
>>>
>>> I don't see the need for ppc to implement pte_next_pfn().
>> 
>> Agreed.
>
> So likely we should then do on top for powerpc (whitespace damage):
>
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index a04ae4449a025..549a440ed7f65 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -220,10 +220,7 @@ void set_ptes(struct mm_struct *mm, unsigned long addr, pte_t *ptep,
>                          break;
>                  ptep++;
>                  addr += PAGE_SIZE;
> -               /*
> -                * increment the pfn.
> -                */
> -               pte = pfn_pte(pte_pfn(pte) + 1, pte_pgprot((pte)));
> +               pte = pte_next_pfn(pte);
>          }
>   }

Agreed.

-aneesh