linux-kernel - Re: [PATCH v2 03/13] mm: Add generic p?d

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Message-ID: <20190221134146.GF33673@lakrids.cambridge.arm.com>
Date:   Thu, 21 Feb 2019 13:41:46 +0000
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.deacon@....com>, 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>
Subject: Re: [PATCH v2 03/13] mm: Add generic p?d_large() macros

On Thu, Feb 21, 2019 at 11:34:52AM +0000, Steven Price wrote:
> From: James Morse <james.morse@....com>
> 
> 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 p?d_large() macros, provided a
> does nothing default.
> 
> Signed-off-by: James Morse <james.morse@....com>
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  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 05e61e6c843f..f0de24100ac6 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -1186,4 +1186,23 @@ static inline bool arch_has_pfn_modify_check(void)
>  #define mm_pmd_folded(mm)	__is_defined(__PAGETABLE_PMD_FOLDED)
>  #endif
>  
> +/*
> + * p?d_large() - true if this entry is a final mapping to a physical address.

It might make sense to s/final/leaf/, but otherwise that's a great
definition!

> + * 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'm not sure if we need this part, since we don't mention
p?d_trans_huge(), etc, but either way:

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

Thanks,
Mark.

> + */
> +#ifndef pgd_large
> +#define pgd_large(x)	0
> +#endif
> +#ifndef p4d_large
> +#define p4d_large(x)	0
> +#endif
> +#ifndef pud_large
> +#define pud_large(x)	0
> +#endif
> +#ifndef pmd_large
> +#define pmd_large(x)	0
> +#endif
> +
>  #endif /* _ASM_GENERIC_PGTABLE_H */
> -- 
> 2.20.1
>