linux-kernel - Re: [PATCH v9 04/21] mips: mm: Add p?d

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Message-ID: <20190722214722.wdlj6a3der3r2oro@pburton-laptop>
Date:   Mon, 22 Jul 2019 21:47:24 +0000
From:   Paul Burton <paul.burton@...s.com>
To:     Steven Price <steven.price@....com>
CC:     "linux-mm@...ck.org" <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" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Mark Rutland <Mark.Rutland@....com>,
        "Liang, Kan" <kan.liang@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ralf Baechle <ralf@...ux-mips.org>,
        James Hogan <jhogan@...nel.org>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>
Subject: Re: [PATCH v9 04/21] mips: mm: Add p?d_leaf() definitions

Hi Steven,

On Mon, Jul 22, 2019 at 04:41:53PM +0100, Steven Price wrote:
> walk_page_range() is going to be allowed to walk page tables other than
> those of user space. For this it needs to know when it has reached a
> 'leaf' entry in the page tables. This information is provided by the
> p?d_leaf() functions/macros.
> 
> For mips, we only support large pages on 64 bit.

That ceases to be true with commit 35476311e529 ("MIPS: Add partial
32-bit huge page support") in mips-next, so I think it may be best to
move the definition to asm/pgtable.h so that both 32b & 64b kernels can
pick it up.

Thanks,
    Paul

> For 64 bit if _PAGE_HUGE is defined we can simply look for it. When not
> defined we can be confident that there are no leaf pages in existence
> and fall back on the generic implementation (added in a later patch)
> which returns 0.
> 
> CC: Ralf Baechle <ralf@...ux-mips.org>
> CC: Paul Burton <paul.burton@...s.com>
> CC: James Hogan <jhogan@...nel.org>
> CC: linux-mips@...r.kernel.org
> Signed-off-by: Steven Price <steven.price@....com>
> ---
>  arch/mips/include/asm/pgtable-64.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/mips/include/asm/pgtable-64.h b/arch/mips/include/asm/pgtable-64.h
> index 93a9dce31f25..2bdbf8652b5f 100644
> --- a/arch/mips/include/asm/pgtable-64.h
> +++ b/arch/mips/include/asm/pgtable-64.h
> @@ -273,6 +273,10 @@ static inline int pmd_present(pmd_t pmd)
>  	return pmd_val(pmd) != (unsigned long) invalid_pte_table;
>  }
>  
> +#ifdef _PAGE_HUGE
> +#define pmd_leaf(pmd)	((pmd_val(pmd) & _PAGE_HUGE) != 0)
> +#endif
> +
>  static inline void pmd_clear(pmd_t *pmdp)
>  {
>  	pmd_val(*pmdp) = ((unsigned long) invalid_pte_table);
> @@ -297,6 +301,10 @@ static inline int pud_present(pud_t pud)
>  	return pud_val(pud) != (unsigned long) invalid_pmd_table;
>  }
>  
> +#ifdef _PAGE_HUGE
> +#define pud_leaf(pud)	((pud_val(pud) & _PAGE_HUGE) != 0)
> +#endif
> +
>  static inline void pud_clear(pud_t *pudp)
>  {
>  	pud_val(*pudp) = ((unsigned long) invalid_pmd_table);
> -- 
> 2.20.1
>