[PATCH v2 2/3] powerpc: mm: add p{te,md,ud}_user_accessible_page helpers

[Christophe Leroy]

Le 23/09/2022 à 08:08, Rohan McLure a écrit :
> Add the following helpers for detecting whether a page table entry
> is a leaf and is accessible to user space.
> 
>   * pte_user_accessible_page
>   * pmd_user_accessible_page
>   * pud_user_accessible_page
> 
> Also implement missing pud_user definitions for both Book3S/E 64-bit
> systems.
> 
> Signed-off-by: Rohan McLure <rmclure at linux.ibm.com>
> ---
> V2: Provide missing pud_user implementations, use p{u,m}d_is_leaf.
> ---

> diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
> index 36956fb440e1..69eed4e03da0 100644
> --- a/arch/powerpc/include/asm/pgtable.h
> +++ b/arch/powerpc/include/asm/pgtable.h
> @@ -172,6 +172,39 @@ static inline int pud_pfn(pud_t pud)
>   }
>   #endif
>   
> +static inline bool pte_user_accessible_page(pte_t pte)
> +{
> +	return pte_present(pte) && pte_user(pte);
> +}
> +
> +#ifdef CONFIG_PPC64
> +
> +static inline bool pmd_user_accessible_page(pmd_t pmd)
> +{
> +	return pmd_is_leaf(pmd) && pmd_present(pmd) && pmd_user(pmd);
> +}
> +
> +static inline bool pud_user_accessible_page(pud_t pud)
> +{
> +	return pud_is_leaf(pud) && pud_present(pud) && pud_user(pud);
> +}
> +
> +#else
> +
> +static inline bool pmd_user_accessible_page(pmd_t pmd)
> +{
> +	WARN(1, "pmd: multi-level paging unsupported on ppc32");
> +	return false;
> +}
> +
> +static inline bool pud_user_accessible_page(pud_t pud)
> +{
> +	WARN(1, "pud: multi-level paging unsupported on ppc32");
> +	return false;
> +}
> +
> +#endif /* CONFIG_PPC64 */
> +


I can't see the point in this splitted implementation PPC64/PPC32.
The warning has no added value from my point of view.

And multi-level paging IS supported on PPC32, that's 2 level paging, the 
PMD is folder into the PGD.

pmd_is_leaf() and pud_is_leaf() are PPC64 specific.

The following could be common to PPC32 and PPC64:

+static inline bool pmd_user_accessible_page(pmd_t pmd)
+{
+	return pmd_leaf(pmd) && pmd_present(pmd) && pmd_user(pmd);
+}
+
+static inline bool pud_user_accessible_page(pud_t pud)
+{
+	return pud_leaf(pud) && pud_present(pud) && pud_user(pud);
+}
+

pud_user() is defined in include/asm-generic/pgtable-nopmd.h for PPC32.

All you have to do is to define a stub pmd_user() for book3s/32 and 
nohash/32.

>   #endif /* __ASSEMBLY__ */
>   
>   #endif /* _ASM_POWERPC_PGTABLE_H */