linux-kernel - Re: [PATCH v17 01/23] mm: Add generic p?d

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Date:   Thu, 19 Dec 2019 22:43:14 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Steven Price <steven.price@....com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     Steven Price <steven.price@....com>,
        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,
        Mark Rutland <Mark.Rutland@....com>,
        "Liang\, Kan" <kan.liang@...ux.intel.com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v17 01/23] mm: Add generic p?d_leaf() macros

Steven Price <steven.price@....com> writes:
> 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 at that level. Futher patches will add implementations for
> individual architectures.
>
> The name p?d_leaf() is chosen to minimize the confusion with existing
> uses of "large" pages and "huge" pages which do not necessary mean that
> the entry is a leaf (for example it may be a set of contiguous entries
> that only take 1 TLB slot). For the purpose of walking the page tables
> we don't need to know how it will be represented in the TLB, but we do
> need to know for sure if it is a leaf of the tree.
>
> Signed-off-by: Steven Price <steven.price@....com>
> Acked-by: Mark Rutland <mark.rutland@....com>
> ---
>  include/asm-generic/pgtable.h | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 798ea36a0549..e2e2bef07dd2 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -1238,4 +1238,24 @@ 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.
> + * Only meaningful when called on a valid entry.
> + */
> +#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

Any reason you made these #defines rather than static inlines?

cheers