linux-kernel - Re: [PATCH 03/22] ARM: LPAE: use phys_addr

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Message-ID: <20120806111413.GB18957@n2100.arm.linux.org.uk>
Date:	Mon, 6 Aug 2012 12:14:13 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Cyril Chemparathy <cyril@...com>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	arnd@...db.de, catalin.marinas@....com, nico@...aro.org,
	will.deacon@....com, Vitaly Andrianov <vitalya@...com>
Subject: Re: [PATCH 03/22] ARM: LPAE: use phys_addr_t on virt <--> phys
	conversion

On Tue, Jul 31, 2012 at 07:04:39PM -0400, Cyril Chemparathy wrote:
> This patch fixes up the types used when converting back and forth between
> physical and virtual addresses.
> 
> Signed-off-by: Vitaly Andrianov <vitalya@...com>
> Signed-off-by: Cyril Chemparathy <cyril@...com>
> ---
>  arch/arm/include/asm/memory.h |   17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index 01c710d..4a0108f 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -157,22 +157,27 @@ extern unsigned long __pv_phys_offset;
>  
>  extern unsigned long __pv_offset;
>  
> -static inline unsigned long __virt_to_phys(unsigned long x)
> +static inline phys_addr_t __virt_to_phys(unsigned long x)
>  {
>  	unsigned long t;
>  	early_patch_imm8(x, t, "add", __pv_offset);
>  	return t;
>  }
>  
> -static inline unsigned long __phys_to_virt(unsigned long x)
> +static inline unsigned long __phys_to_virt(phys_addr_t x)
>  {
>  	unsigned long t;
>  	early_patch_imm8(x, t, "sub", __pv_offset);
>  	return t;
>  }
>  #else
> -#define __virt_to_phys(x)	((x) - PAGE_OFFSET + PHYS_OFFSET)
> -#define __phys_to_virt(x)	((x) - PHYS_OFFSET + PAGE_OFFSET)
> +
> +#define __virt_to_phys(x)		\
> +	((phys_addr_t)(x) - PAGE_OFFSET + PHYS_OFFSET)
> +
> +#define __phys_to_virt(x)		\
> +	((unsigned long)((phys_addr_t)(x) - PHYS_OFFSET + PAGE_OFFSET))
> +
>  #endif
>  #endif
>  
> @@ -207,14 +212,14 @@ static inline phys_addr_t virt_to_phys(const volatile void *x)
>  
>  static inline void *phys_to_virt(phys_addr_t x)
>  {
> -	return (void *)(__phys_to_virt((unsigned long)(x)));
> +	return (void *)__phys_to_virt(x);
>  }
>  
>  /*
>   * Drivers should NOT use these either.
>   */
>  #define __pa(x)			__virt_to_phys((unsigned long)(x))
> -#define __va(x)			((void *)__phys_to_virt((unsigned long)(x)))
> +#define __va(x)			((void *)__phys_to_virt((phys_addr_t)(x)))
>  #define pfn_to_kaddr(pfn)	__va((pfn) << PAGE_SHIFT)

This as a whole does not fill me with a great amount of enthusiasm,
because it breaks some of the typechecking that we have here.

The whole point of __phys_to_virt() and __virt_to_phys() is that they work
on integer types, and warn if you dare to use them with pointers.  Adding
a cast into them breaks that.

The whole point is that the typecasting is explicitly inside phys_to_virt()
and virt_to_phys() and not their macro counterparts.

Secondly, are you sure that this patch is correct on its own?  You're
passing a u64 into assembly only expecting a 32-bit register.  Have you
checked it does the right thing with a 64-bit phys_addr_t on both LE
and BE?
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