[PATCH 2/3] ARM: mm: fix __phys_to_virt to work with 64 bit phys_addr_t in BE case

[santosh.shilimkar@ti.com (Santosh Shilimkar)]

On Monday 04 November 2013 09:16 PM, Victor Kamensky wrote:
> Make sure that inline assembler that expects 'r' operand
> receives 32 bit value.
> 
> Before this fix in case of CONFIG_ARCH_PHYS_ADDR_T_64BIT and
> CONFIG_ARM_PATCH_PHYS_VIRT __phys_to_virt function passed 64 bit
> value to __pv_stub inline assembler where 'r' operand is
> expected. Compiler behavior in such case is not well specified.
> It worked in little endian case, but in big endian case
> incorrect code was generated, where compiler confused which
> part of 64 bit value it needed to modify. For example BE
> snippet looked like this:
> 
> N:0x80904E08 : MOV      r2,#0
> N:0x80904E0C : SUB      r2,r2,#0x81000000
> 
> when LE similar code looked like this
> 
> N:0x808FCE2C : MOV      r2,r0
> N:0x808FCE30 : SUB      r2,r2,#0xc0, 8 ; #0xc0000000
> 
> Note 'r0' register is va that have to be translated into phys
> 
> To avoid this situation use explicit cast to 'unsigned long',
> which explicitly discard upper part of phys address and convert
> value to 32 bit. Also add comment so such cast will not be
> removed in the future.
> 
> Signed-off-by: Victor Kamensky <victor.kamensky@linaro.org>
> ---
>  arch/arm/include/asm/memory.h | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index 4dd2145..7a8599c 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -226,7 +226,13 @@ static inline phys_addr_t __virt_to_phys(unsigned long x)
>  static inline unsigned long __phys_to_virt(phys_addr_t x)
>  {
>  	unsigned long t;
> -	__pv_stub(x, t, "sub", __PV_BITS_31_24);
Minor nit. An extra line would be good here for a comment to follow.
> +        /*
> +         * 'unsigned long' cast discard upper word when
> +         * phys_addr_t is 64 bit, and makes sure that inline
> +         * assembler expression receives 32 bit argument
> +         * in place where 'r' 32 bit operand is expected.
> +         */
> +	__pv_stub((unsigned long) x, t, "sub", __PV_BITS_31_24);
>  	return t;
>  }
>  
> 
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>