linux-kernel - Re: [PATCHv3 02/11] arm64: Handle section maps for swapper/idmap

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Message-ID: <20151014120618.GB2150@leverpostej>
Date:	Wed, 14 Oct 2015 13:06:18 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	"Suzuki K. Poulose" <suzuki.poulose@....com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	catalin.marinas@....com, will.deacon@....com,
	steve.capper@...aro.org, marc.zyngier@....com,
	ard.biesheuvel@...aro.org, christoffer.dall@...aro.org
Subject: Re: [PATCHv3 02/11] arm64: Handle section maps for swapper/idmap

On Wed, Oct 14, 2015 at 12:20:25PM +0100, Suzuki K. Poulose wrote:
> We use section maps with 4K page size to create the swapper/idmaps.
> So far we have used !64K or 4K checks to handle the case where we
> use the section maps.
> This patch adds a new symbol, ARM64_SWAPPER_USES_SECTION_MAPS, to
> handle cases where we use section maps, instead of using the page size
> symbols.
> 
> Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will.deacon@....com>
> Signed-off-by: Suzuki K. Poulose <suzuki.poulose@....com>
> ---
>  arch/arm64/include/asm/kernel-pgtable.h |   31 ++++++++-----
>  arch/arm64/mm/mmu.c                     |   72 ++++++++++++++-----------------
>  2 files changed, 52 insertions(+), 51 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kernel-pgtable.h b/arch/arm64/include/asm/kernel-pgtable.h
> index 622929d..5876a36 100644
> --- a/arch/arm64/include/asm/kernel-pgtable.h
> +++ b/arch/arm64/include/asm/kernel-pgtable.h
> @@ -19,6 +19,13 @@
>  #ifndef __ASM_KERNEL_PGTABLE_H
>  #define __ASM_KERNEL_PGTABLE_H
>  
> +/* With 4K pages, we use section maps. */
> +#ifdef CONFIG_ARM64_4K_PAGES
> +#define ARM64_SWAPPER_USES_SECTION_MAPS 1
> +#else
> +#define ARM64_SWAPPER_USES_SECTION_MAPS 0
> +#endif

The comment is somewhat redunant. It would be better to state why we do
this for 4K and not 64K (or 16K).

> @@ -406,14 +407,11 @@ static void __init map_mem(void)
>  	 * memory addressable from the initial direct kernel mapping.
>  	 *
>  	 * The initial direct kernel mapping, located at swapper_pg_dir, gives
> -	 * us PUD_SIZE (4K pages) or PMD_SIZE (64K pages) memory starting from
> -	 * PHYS_OFFSET (which must be aligned to 2MB as per
> -	 * Documentation/arm64/booting.txt).
> +	 * us PUD_SIZE (with SECTION maps, i.e, 4K) or PMD_SIZE (without
> +	 * SECTION maps, i.e, 64K pages) memory starting from PHYS_OFFSET
> +	 * (which must be aligned to 2MB as per Documentation/arm64/booting.txt).

This didn't seem to get updated for 16K later in the series, unless I
missed something.

Perhaps drop the mention of 4K / 64K entirely here?

> @@ -551,7 +552,7 @@ int kern_addr_valid(unsigned long addr)
>  	return pfn_valid(pte_pfn(*pte));
>  }
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP
> -#ifdef CONFIG_ARM64_64K_PAGES
> +#if !ARM64_SWAPPER_USES_SECTION_MAPS

This leaves the comments on the #else and #endif stale. Please update
those too.

Otherwise this looks good!

Thanks,
Mark.
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