Re: [PATCH v5 01/25] mm: Clarify the spec for set_ptes()

David Hildenbrand
2024-02-12T12:03:08Z

On 02.02.24 09:07, Ryan Roberts wrote:
> set_ptes() spec implies that it can only be used to set a present pte
> because it interprets the PFN field to increment it. However,
> set_pte_at() has been implemented on top of set_ptes() since set_ptes()
> was introduced, and set_pte_at() allows setting a pte to a not-present
> state. So clarify the spec to state that when nr==1, new state of pte
> may be present or not present. When nr>1, new state of all ptes must be
> present.
>
> While we are at it, tighten the spec to set requirements around the
> initial state of ptes; when nr==1 it may be either present or
> not-present. But when nr>1 all ptes must initially be not-present. All
> set_ptes() callsites already conform to this requirement. Stating it
> explicitly is useful because it allows for a simplification to the
> upcoming arm64 contpte implementation.
>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
> include/linux/pgtable.h | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
> index f0feae7f89fb..5e7eaf8f2b97 100644
> --- a/include/linux/pgtable.h
> +++ b/include/linux/pgtable.h
> @@ -229,6 +229,10 @@ static inline pte_t pte_next_pfn(pte_t pte)
> * @pte: Page table entry for the first page.
> * @nr: Number of pages to map.
> *
> + * When nr==1, initial state of pte may be present or not present, and new state
> + * may be present or not present. When nr>1, initial state of all ptes must be
> + * not present, and new state must be present.
> + *
> * May be overridden by the architecture, or the architecture can define
> * set_pte() and PFN_PTE_SHIFT.
> *

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

--
Cheers,

David / dhildenb