diff mbox series

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

Message ID 20240202080756.1453939-2-ryan.roberts@arm.com
State New
Headers
Series Transparent Contiguous PTEs for User Mappings |

Commit Message

Ryan Roberts Feb. 2, 2024, 8:07 a.m. UTC 
  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(+)

Comments

David Hildenbrand Feb. 12, 2024, 12:03 p.m. UTC | #1 
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>
diff mbox series

Patch

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.
  *