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SubjectRe: [PATCH v9 10/21] mm: Add generic p?d_leaf() macros
On Mon, Jul 22, 2019 at 04:41:59PM +0100, Steven Price wrote:
> Exposing the pud/pgd levels of the page tables to walk_page_range() means
> we may come across the exotic large mappings that come with large areas
> of contiguous memory (such as the kernel's linear map).
>
> For architectures that don't provide all p?d_leaf() macros, provide
> generic do nothing default that are suitable where there cannot be leaf
> pages that that level.
>
> Signed-off-by: Steven Price <steven.price@arm.com>

Not a big deal, but it would probably make sense for this to be patch 1
in the series, given it defines the semantic of p?d_leaf(), and they're
not used until we provide all the architectural implemetnations anyway.

It might also be worth pointing out the reasons for this naming, e.g.
p?d_large() aren't currently generic, and this name minimizes potential
confusion between p?d_{large,huge}().

> ---
> include/asm-generic/pgtable.h | 19 +++++++++++++++++++
> 1 file changed, 19 insertions(+)
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 75d9d68a6de7..46275896ca66 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -1188,4 +1188,23 @@ static inline bool arch_has_pfn_modify_check(void)
> #define mm_pmd_folded(mm) __is_defined(__PAGETABLE_PMD_FOLDED)
> #endif
>
> +/*
> + * p?d_leaf() - true if this entry is a final mapping to a physical address.
> + * This differs from p?d_huge() by the fact that they are always available (if
> + * the architecture supports large pages at the appropriate level) even
> + * if CONFIG_HUGETLB_PAGE is not defined.
> + */

I assume it's only safe to call these on valid entries? I think it would
be worth calling that out explicitly.

Otherwise, this looks sound to me:

Acked-by: Mark Rutland <mark.rutland@arm.com>

Thanks,
Mark.
> +#ifndef pgd_leaf
> +#define pgd_leaf(x) 0
> +#endif
> +#ifndef p4d_leaf
> +#define p4d_leaf(x) 0
> +#endif
> +#ifndef pud_leaf
> +#define pud_leaf(x) 0
> +#endif
> +#ifndef pmd_leaf
> +#define pmd_leaf(x) 0
> +#endif
> +
> #endif /* _ASM_GENERIC_PGTABLE_H */
> --
> 2.20.1
>

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