linux-kernel - Re: [PATCH v2 2/9] mm: move __phys_to_pfn and __pfn_to_phys to asm/generic/memory

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Date:	Tue, 29 Sep 2015 15:21:39 -0400 (EDT)
From:	Nicolas Pitre <nicolas.pitre@...aro.org>
To:	Dan Williams <dan.j.williams@...el.com>
cc:	Russell King <linux@....linux.org.uk>, linux-nvdimm@...ts.01.org,
	boaz@...xistor.com, david@...morbit.com,
	linux-kernel@...r.kernel.org, hch@....de, linux-mm@...ck.org,
	hpa@...or.com, ross.zwisler@...ux.intel.com, mingo@...nel.org
Subject: Re: [PATCH v2 2/9] mm: move __phys_to_pfn and __pfn_to_phys to
 asm/generic/memory_model.h

On Tue, 25 Aug 2015, Dan Williams wrote:

> From: Christoph Hellwig <hch@....de>
> 
> Three architectures already define these, and we'll need them genericly
> soon.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  arch/arm/include/asm/memory.h       |    6 ------
>  arch/arm64/include/asm/memory.h     |    6 ------
>  arch/unicore32/include/asm/memory.h |    6 ------
>  include/asm-generic/memory_model.h  |    6 ++++++
>  4 files changed, 6 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index b7f6fb462ea0..98d58bb04ac5 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -119,12 +119,6 @@
>  #endif
>  
>  /*
> - * Convert a physical address to a Page Frame Number and back
> - */
> -#define	__phys_to_pfn(paddr)	((unsigned long)((paddr) >> PAGE_SHIFT))
> -#define	__pfn_to_phys(pfn)	((phys_addr_t)(pfn) << PAGE_SHIFT)
> -
> -/*
>   * Convert a page to/from a physical address
>   */
>  #define page_to_phys(page)	(__pfn_to_phys(page_to_pfn(page)))

[...]

> diff --git a/include/asm-generic/memory_model.h b/include/asm-generic/memory_model.h
> index 14909b0b9cae..f20f407ce45d 100644
> --- a/include/asm-generic/memory_model.h
> +++ b/include/asm-generic/memory_model.h
> @@ -69,6 +69,12 @@
>  })
>  #endif /* CONFIG_FLATMEM/DISCONTIGMEM/SPARSEMEM */
>  
> +/*
> + * Convert a physical address to a Page Frame Number and back
> + */
> +#define	__phys_to_pfn(paddr)	((unsigned long)((paddr) >> PAGE_SHIFT))
> +#define	__pfn_to_phys(pfn)	((pfn) << PAGE_SHIFT)
> +

This patch, currently in mainline as commit 012dcef3f0, breaks LPAE on 
ARM32 with more than 4GB of RAM. The phys_addr_t cast in the original 
ARM definition is important when LPAE is enabled as phys_addr_t is 64 
bits while longs are 32 bits.


Nicolas
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