linux-kernel - Re: [PATCH V2] arm64/mm: Simplify and document pte_to

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Message-ID: <CAMj1kXF2NyZS7cWiZiPBuySdFnpB_gcHa4KXieje4_G1-zCmog@mail.gmail.com>
Date:   Mon, 7 Nov 2022 13:02:00 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Anshuman Khandual <anshuman.khandual@....com>
Cc:     linux-arm-kernel@...ts.infradead.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Mark Brown <broonie@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2] arm64/mm: Simplify and document pte_to_phys() for 52
 bit addresses

Hello Anshuman,

On Mon, 7 Nov 2022 at 12:49, Anshuman Khandual
<anshuman.khandual@....com> wrote:
>
> pte_to_phys() assembly definition does multiple bits field transformations
> to derive physical address, embedded inside a page table entry. Unlike its
> C counter part i.e __pte_to_phys(), pte_to_phys() is not very apparent. It
> simplifies these operations via a new macro PTE_ADDR_HIGH_SHIFT indicating
> how far the pte encoded higher address bits need to be left shifted. While
> here, this also updates __pte_to_phys() and __phys_to_pte_val().
>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Brown <broonie@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Suggested-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>

With the nit below fixed, this looks good to me

Reviewed-by: Ard Biesheuvel <ardb@...nel.org>

> ---
> This applies on v6.1-rc4
>
> Changes in V2:
>
> - Added PTE_ADDR_HIGH_SHIFT based method per Ard
>
> Changes in V1:
>
> https://lore.kernel.org/all/20221031082421.1957288-1-anshuman.khandual@arm.com/
>
>  arch/arm64/include/asm/assembler.h     | 8 +++-----
>  arch/arm64/include/asm/pgtable-hwdef.h | 1 +
>  arch/arm64/include/asm/pgtable.h       | 4 ++--
>  3 files changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/assembler.h b/arch/arm64/include/asm/assembler.h
> index e5957a53be39..6a39a3601cf7 100644
> --- a/arch/arm64/include/asm/assembler.h
> +++ b/arch/arm64/include/asm/assembler.h
> @@ -660,12 +660,10 @@ alternative_endif
>         .endm
>
>         .macro  pte_to_phys, phys, pte
> -#ifdef CONFIG_ARM64_PA_BITS_52
> -       ubfiz   \phys, \pte, #(48 - 16 - 12), #16
> -       bfxil   \phys, \pte, #16, #32
> -       lsl     \phys, \phys, #16
> -#else
>         and     \phys, \pte, #PTE_ADDR_MASK
> +#ifdef CONFIG_ARM64_PA_BITS_52
> +       orr \phys, \phys, \phys, lsl #PTE_ADDR_HIGH_SHIFT
> +       and \phys, \phys, GENMASK_ULL(PHYS_MASK_SHIFT - 1, PAGE_SHIFT)

Please use tabs between the mnemonics and the arguments.

>  #endif
>         .endm
>
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index 5ab8d163198f..f658aafc47df 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -159,6 +159,7 @@
>  #ifdef CONFIG_ARM64_PA_BITS_52
>  #define PTE_ADDR_HIGH          (_AT(pteval_t, 0xf) << 12)
>  #define PTE_ADDR_MASK          (PTE_ADDR_LOW | PTE_ADDR_HIGH)
> +#define PTE_ADDR_HIGH_SHIFT    36
>  #else
>  #define PTE_ADDR_MASK          PTE_ADDR_LOW
>  #endif
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 71a1af42f0e8..daedd6172227 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -77,11 +77,11 @@ extern unsigned long empty_zero_page[PAGE_SIZE / sizeof(unsigned long)];
>  static inline phys_addr_t __pte_to_phys(pte_t pte)
>  {
>         return (pte_val(pte) & PTE_ADDR_LOW) |
> -               ((pte_val(pte) & PTE_ADDR_HIGH) << 36);
> +               ((pte_val(pte) & PTE_ADDR_HIGH) << PTE_ADDR_HIGH_SHIFT);
>  }
>  static inline pteval_t __phys_to_pte_val(phys_addr_t phys)
>  {
> -       return (phys | (phys >> 36)) & PTE_ADDR_MASK;
> +       return (phys | (phys >> PTE_ADDR_HIGH_SHIFT)) & PTE_ADDR_MASK;
>  }
>  #else
>  #define __pte_to_phys(pte)     (pte_val(pte) & PTE_ADDR_MASK)
> --
> 2.25.1
>