linux-kernel - Re: [PATCH v2 06/22] ARM: LPAE: use signed arithmetic for mask definitions

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Message-ID: <alpine.LFD.2.02.1208112356470.5231@xanadu.home>
Date:	Sat, 11 Aug 2012 23:57:41 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Cyril Chemparathy <cyril@...com>
cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	arnd@...db.de, catalin.marinas@....com, grant.likely@...retlab.ca,
	linux@....linux.org.uk, will.deacon@....com,
	Vitaly Andrianov <vitalya@...com>
Subject: Re: [PATCH v2 06/22] ARM: LPAE: use signed arithmetic for mask
 definitions

On Fri, 10 Aug 2012, Cyril Chemparathy wrote:

> This patch applies to PAGE_MASK, PMD_MASK, and PGDIR_MASK, where forcing
> unsigned long math truncates the mask at the 32-bits.  This clearly does bad
> things on PAE systems.
> 
> This patch fixes this problem by defining these masks as signed quantities.
> We then rely on sign extension to do the right thing.
> 
> Signed-off-by: Cyril Chemparathy <cyril@...com>
> Signed-off-by: Vitaly Andrianov <vitalya@...com>

Reviewed-by: Nicolas Pitre <nico@...aro.org>

> ---
>  arch/arm/include/asm/page.h           |    2 +-
>  arch/arm/include/asm/pgtable-3level.h |    6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/include/asm/page.h b/arch/arm/include/asm/page.h
> index ecf9019..1e0fe08 100644
> --- a/arch/arm/include/asm/page.h
> +++ b/arch/arm/include/asm/page.h
> @@ -13,7 +13,7 @@
>  /* PAGE_SHIFT determines the page size */
>  #define PAGE_SHIFT		12
>  #define PAGE_SIZE		(_AC(1,UL) << PAGE_SHIFT)
> -#define PAGE_MASK		(~(PAGE_SIZE-1))
> +#define PAGE_MASK		(~((1 << PAGE_SHIFT) - 1))
>  
>  #ifndef __ASSEMBLY__
>  
> diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
> index b249035..ae39d11 100644
> --- a/arch/arm/include/asm/pgtable-3level.h
> +++ b/arch/arm/include/asm/pgtable-3level.h
> @@ -48,16 +48,16 @@
>  #define PMD_SHIFT		21
>  
>  #define PMD_SIZE		(1UL << PMD_SHIFT)
> -#define PMD_MASK		(~(PMD_SIZE-1))
> +#define PMD_MASK		(~((1 << PMD_SHIFT) - 1))
>  #define PGDIR_SIZE		(1UL << PGDIR_SHIFT)
> -#define PGDIR_MASK		(~(PGDIR_SIZE-1))
> +#define PGDIR_MASK		(~((1 << PGDIR_SHIFT) - 1))
>  
>  /*
>   * section address mask and size definitions.
>   */
>  #define SECTION_SHIFT		21
>  #define SECTION_SIZE		(1UL << SECTION_SHIFT)
> -#define SECTION_MASK		(~(SECTION_SIZE-1))
> +#define SECTION_MASK		(~((1 << SECTION_SHIFT) - 1))
>  
>  #define USER_PTRS_PER_PGD	(PAGE_OFFSET / PGDIR_SIZE)
>  
> -- 
> 1.7.9.5
> 
--
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