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Message-ID: <20190723094113.GA8085@lakrids.cambridge.arm.com>
Date: Tue, 23 Jul 2019 10:41:14 +0100
From: Mark Rutland <mark.rutland@....com>
To: Steven Price <steven.price@....com>
Cc: linux-mm@...ck.org, Andy Lutomirski <luto@...nel.org>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
Catalin Marinas <catalin.marinas@....com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Ingo Molnar <mingo@...hat.com>,
James Morse <james.morse@....com>,
Jérôme Glisse <jglisse@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Thomas Gleixner <tglx@...utronix.de>,
Will Deacon <will@...nel.org>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
"Liang, Kan" <kan.liang@...ux.intel.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [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@....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@....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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