linux-kernel - Re: [PATCH] arm64/mm: Drop SECTION

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Date:   Mon, 14 Jun 2021 22:40:17 +1000
From:   Gavin Shan <gshan@...hat.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64/mm: Drop SECTION_[SHIFT|SIZE|MASK]

On 6/14/21 6:18 PM, Anshuman Khandual wrote:
> SECTION_[SHIFT|SIZE|MASK] are essentially PMD_[SHIFT|SIZE|MASK]. But these
> create confusion being similar to generic sparsemem memory sections, which
> are derived from SECTION_SIZE_BITS. Section references have always implied
> PMD level block mapping. Instead just use all PMD level macros which would
> make it explicit and also remove confusion with sparsmem memory sections.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> This applies on v5.13-rc6.
> 
>   arch/arm64/include/asm/kernel-pgtable.h | 4 ++--
>   arch/arm64/include/asm/pgtable-hwdef.h  | 7 -------
>   arch/arm64/mm/mmu.c                     | 2 +-
>   3 files changed, 3 insertions(+), 10 deletions(-)
> 

It does introduce confusion to sparsemem section. The changes look
good to me:

Reviewed-by: Gavin Shan <gshan@...hat.com>

> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index d44df9d62fc9..88b8d681ad91 100644
> --- a/arch/arm64/include/asm/kernel-pgtable.h
> +++ b/arch/arm64/include/asm/kernel-pgtable.h
> @@ -91,8 +91,8 @@
>   
>   /* Initial memory map size */
>   #if ARM64_SWAPPER_USES_SECTION_MAPS
> -#define SWAPPER_BLOCK_SHIFT	SECTION_SHIFT
> -#define SWAPPER_BLOCK_SIZE	SECTION_SIZE
> +#define SWAPPER_BLOCK_SHIFT	PMD_SHIFT
> +#define SWAPPER_BLOCK_SIZE	PMD_SIZE
>   #define SWAPPER_TABLE_SHIFT	PUD_SHIFT
>   #else
>   #define SWAPPER_BLOCK_SHIFT	PAGE_SHIFT
> diff --git a/arch/arm64/include/asm/pgtable-hwdef.h b/arch/arm64/include/asm/pgtable-hwdef.h
> index b82575a33f8b..40085e53f573 100644
> --- a/arch/arm64/include/asm/pgtable-hwdef.h
> +++ b/arch/arm64/include/asm/pgtable-hwdef.h
> @@ -71,13 +71,6 @@
>   #define PGDIR_MASK		(~(PGDIR_SIZE-1))
>   #define PTRS_PER_PGD		(1 << (VA_BITS - PGDIR_SHIFT))
>   
> -/*
> - * Section address mask and size definitions.
> - */
> -#define SECTION_SHIFT		PMD_SHIFT
> -#define SECTION_SIZE		(_AC(1, UL) << SECTION_SHIFT)
> -#define SECTION_MASK		(~(SECTION_SIZE-1))
> -
>   /*
>    * Contiguous page definitions.
>    */
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 89b66ef43a0f..380771610dd2 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -228,7 +228,7 @@ static void init_pmd(pud_t *pudp, unsigned long addr, unsigned long end,
>   		next = pmd_addr_end(addr, end);
>   
>   		/* try section mapping first */
> -		if (((addr | next | phys) & ~SECTION_MASK) == 0 &&
> +		if (((addr | next | phys) & ~PMD_MASK) == 0 &&
>   		    (flags & NO_BLOCK_MAPPINGS) == 0) {
>   			pmd_set_huge(pmdp, phys, prot);
>   
>